Detailed explanations in West Bengal Board Class 9 Geography Book Solutions Chapter 3 Determination of Location of a Place on the Earth’s Surface offer valuable context and analysis.

## WBBSE Class 9 Geography Chapter 3 Question Answer – Determination of Location of a Place on the Earth’s Surface

Very Short Questions and Answers : (1 mark for each question)

Question 1.

What is the latitude of the Arctic Circle?

Answer:

66 1/2° N.

Question 2.

What are lines of longitude also known as?

Answer:

Meridians of longitude.

Question 3.

What is Prime Meridian also known as?

Answer:

Greenwich Meridian.

Question 4.

What is the latitude of the Tropic of Capricorn?

Answer:

23 1/2°

Question 5.

What are latitudes also known as?

Answer:

Parallels of latitude.

Question 6.

What is the angular distance of a place, east or west of the Prime Meridian known as?

Answer:

Longitude.

Question 7.

What is 90° N also known as?

Answer:

North Pole.

Question 8.

What is 90° S also known as?

Answer:

South Pole.

Question 9.

Which natural object can be used to calculate time?

Answer:

Sun.

Question 10.

What is the other name for local mean time?

Answer:

Solar time.

Question 11.

Who invented the chronometer?

Answer:

John Harrison.

Question 12.

What is the linear distance between two lines of longitude, at an interval of 1^{\circ, along the equator?

Answer:

111.3 km.

Question 13.

What is located at the antipode of the Prime Meridian?

Answer:

180° or the International Date Line.

Question 14.

What is the time difference between IST and GMT?

Answer:

5 h and 30 m.

Question 15.

What is the time difference between a place and its antipode?

Answer:

12 hours.

Question 16.

What is the longitudinal difference between a place and its antipode?

Answer:

180°

Question 17.

How many artificial satellites were launched by the USA to determine the location of any place on earth?

Answer:

24.

Question 18.

Name the latitude that is located at an equal distance from either of the poles.

Answer:

The equator.

Question 19.

How much time is gained while crossing the International Date Line from the Western Hemisphere?

Answer:

24 hours or 1 day.

Question 20.

When and where was the International Meridian Conference held?

Answer:

October, 1884 in Washington D. C.

Question 21.

Name the imaginary plane that passes through the equator and is perpendicular to the earth’s axis.

Answer:

Equatorial plane.

Question 22.

Which state of India experiences sunrise first?

Answer:

Arunachal Pradesh.

Short Questions and Answers : (2 marks for each question)

Question 1.

What is meant by parallels of latitude?

Answer:

The imaginary lines drawn around the earth, which run parallel to the equator are known as the parallels of latitude. They are also called lines of latitude. These lines join all places having the same latitudinal degree or angular distance from the equator. For example, the Tropic of Cancer (23 1/2° N).

Question 2.

What is meant by meridian?

Answer:

In geography, a meridian is the half of an imaginary great circle on the surface of the earth, that ends at the geographical polesThe North Pole and the South Pole. It connects all the points of equal longitude. Each meridian is of equal length and is perpendicular to all the circles of latitude.

Question 3.

What are the properties of latitudes?

Answer:

The properties of latitudes are as follows-

- All the latitudes are full circles and run parallel to each other.
- Latitudes run in an east-west direction.
- As the angular distance of a place north or south of the equator increases, the circumference of the circle of latitude decreases.
- The local time of the places lying on the same latitude are always different.

Question 4.

What are the properties of lines of longitude?

Answer:

The properties of lines of longitude are as follows-

- All the longitudes are half circles.
- All the longitudes are of equal length.
- The longitudes run in a north-south direction.
- The local time of the places lying on the same longitude are always same.

Question 5.

What is the equator?

Answer:

The equator is the imaginary east-west line encircling the earth midway between the North and South poles. The equator is the 0° latitude. It divides the earth into two equal halves called the Northern Hemisphere and the Southern Hemisphere. The average circumference of the equator is 40,000 km.

Question 6.

What is the Prime Meridian?

Answer:

Prime Meridian is the notional line drawn from the North Pole to the South Pole that passes through Greenwich and is designated as the 0° longitude. All other longitudes are measured from this line. The Greenwich Meridian divides the earth into two equal halves – the Eastern and Western hemispheres.

Question 7.

What is the Hadley’s Octans? From where is it visible?

Answer:

Hadley’s Octans is a constellation of stars in the southern sky that appears to circle around the south celestial pole. This constellation is faintly visible from any place in the Southern Hemisphere. However, it is difficult to view this with naked eyes.

Question 8.

What is meant by latitude?

Answer:

The angular distance of a place, north or south of the equator, usually measured in degrees is known as latitude. All the places having the same latitudinal degree, if joined by a single line, forms the parallel. For example, the latitude of Kolkata is 22° 30′ N.

Question 9.

What is meant by longitude?

Answer:

The angular distance of a place, east or west of the Greenwich meridian, usually measured in degrees is known as longitude. All the places having the same longitudinal degree, if joined by a single line, forms the meridian. For example, the longitude of Kolkata is 88° 30′ E.

Question 10.

What is local time?

Answer:

The time of a place as determined according to noon or when the sun is directly overhead the meridian passing through that place, is called local time. The earth rotates around its axis once in every 24 hours, and during the course of this rotation, sunrays fall vertically overhead at different places at different times. Local time is also determined using the angle of elevation of the sun at that place.

Question 11.

What is standard time?

Answer:

The time of any country as standardised according to the local time at its Standard Meridian or the longitude passing through the middle of that country, is called standard time. The time of a country can be determined from this.

Question 12.

What is meant by antipode?

Answer:

The antipode of a point is the point on the earth’s surface which is diametrically opposite to it. The two points which are antipodal to one another can be connected by a straight line running through the centre of the earth.

Question 13.

What is the International Date Line?

Answer:

The International Date Line is an imaginary line that mostly follows the 180° longitude but deviates from its position near the Aleutian Islands, the Fiji and Chatham Islands. The International Date Line acts as a dividing line between the dates of the Eastern and Western Hemispheres. According to this line, the calendar dates are changed.

Question 14.

What is meant by equatorial plane?

Answer:

The plane that passes through the equator and cuts the earth into two equal halves is called the equatorial plane. The centre of the earth lies on this plane and so, the angular value of this plane is 0°. It is perpendicular to the earth’s axis.

Question 15.

What is a sextant?

Answer:

A sextant is an instrument used to determine the angle between a celestial object and the horizon (this angle is also known as the object’s altitude). The instrument has an in-built telescope and helps in determining the latitude of a place.

Question 16.

What is a Chronometer?

Answer:

Chronometer is a precise and accurate clock, used to determine the longitude at sea. In 1735, John Harrison built the first chronometer, which he improved, with many innovations, over the next thirty years before submitting it for examination. The most complete international collection of chronometers, including the Harrison’s, is at the Royal Observatory, in London, England.

Question 17.

What is the difference between a great circle and a small circle?

Answer:

A circle formed on the surface of a sphere by a plane that passes through the centre of the sphere is called a great circle. It is different from a small circle in the sense that, a small circle is formed on the surface of a sphere by a plane that does not pass through the centre of the sphere. For example, the equator (0°) is a great circle whereas, both the Tropics (23 1/2°) are small circles.

Question 18.

How are longitude and time related?

Answer:

Determination and calculation of time is greatly dependent on the lines of longitude. The time for a particular longitude is calculated on the basis of noon time or 120′ clock midday of that place. We know that, for every 1° difference in longitude, there is a time difference of 4 minutes. Moreover, if the time difference between any two places is known, the longitudinal difference of those two places can be easily determined.

Question 19.

Why does high temperature prevail in the torrid zone all through the year?

Answer:

The torrid zone extends between the Tropic of Cancer (231° N) and the Tropic of Capricorn (23 1/2° S). The apparent motion of the sun is also restricted between these tropics. From December 22 upto June 21 the sun apparently moves from Tropic of Capricorn to Tropic of Cancer that is known as the apparent northward movement of the sun. Similarly from June 21 till December 22 the sun apparently moves in the opposite direction that is known as the apparent southward movement of the sun. Therefore, this region receives vertical rays of the sun all year, and this is why high temperatures (25°-35° C) prevail.

Question 20.

At which places does the International Date Line deviate from the 180° longitude?

Answer:

The International Date Line is not a straight line, but moves in a zigzag manner to avoid crossing through any landmass. In the Northern Hemisphere, the International Date Line is displaced eastwards to avoid the Wrangel island and then deviates west to avoid the Bering Sea and almost 7° to avoid Aleutian Islands. In the Southern Hemisphere, the International Date Line deviates almost 11° to avoid Fiji, Chatham and such other islands.

Question 21.

What is meant by graticule?

Answer:

Graticule is a network or web of lines representing the earth’s parallels of latitude and meridians of longitude, on which maps are drawn. The combination of these two components specify the position of any place on the earth. However, it does not consider the altitude or depth of a place.

Question 22.

What is meant by angular distance?

Answer:

An angle whose apex is at the centre of the spherical earth and whose legs are radii intersecting the circle in two distinct points, thereby subtending an arc between those two points is known as the angular distance. The unit used to measure the angular distance is degree, minute and seconds as it is conceptually identical to an angle.

Question 23.

What are Arctic and Antarctic Circles?

Answer:

Arctic Circle is the parallel of latitude that runs 661° north of the equator, whereas, Antarctic Circle is the parallel of latitude that runs 66 1/2° south of the equator. The region beyond the Arctic and the Antarctic circles experience 6 months of complete daylight and 6 months of complete darkness throughout the year.

Question 24.

What is the time difference between a place and its antipode?

Answer:

The longitudinal difference between any place and its antipodal point is 180°. We know that, for every 1° longitudinal difference time difference experienced is 4 minute. Therefore, the time difference between the place and its antipodal point becomes (180 × 4 = 720 minute) 12 hours.

Question 25.

What is meant by the northern and the southern latitudes?

Answer:

The latitudes can be delineated into two types on the basis of which hemisphere it is located-

1. Northern latitudes: Latitudes located to the north of the equator are known as northern latitudes. So, all the latitudes from 1° to 90° in the Northern Hemisphere come under this. These are denoted by the letter ‘N’.

2. Southern latitudes: Latitudes located towards the south of the equator are known as the southern latitudes. So, all the latitudes from 1° to 90° in the Southern Hemisphere come under this. These are denoted by the letter ‘S’.

Question 26.

What is the Standard Meridian for India? Through which place does it pass?

Answer:

India, in the Eastern Hemisphere, has a vast longitudinal extension i.e., from 68° 07′ E to 97° 25′ E. The 82 1/2° E longitude is taken as the Standard Meridian for the country and the local time of this meridian is considered as the standard time for entire India. It is known as the Indian Standard Time (IST).The IST passes through the city of Allahabad. Therefore, the local time of Allahabad is taken as the standard time for India.

Question 27.

What is a sundial?

Answer:

Sundial is the earliest timekeeping device, that indicates the time of day by the position of the shadow of some object open to the sun’s rays. As the day advances, sun moves across the sky, causing shadow of the object to move and indicating the passage of time. The flat surface of the sundial is called the dial plate, that is generally made out of materials like wood, stone, metal and such others.

Question 28.

Name the standard meridians of the U.S.A.

Answer:

A country with a greater east-west expanse, like the USA, may have more than one standard time. These are known as time zones. The United States of America has 4 time zones. They are as follows-

- Eastern Standard Time (EST): This time zone is 5 hours behind G.M.T. New York falls in this time zone.
- Central Standard Time (CST): This time zone is 6 hours behind G.M.T. Chicago falls in this time zone.
- Mountain Standard Time (MST): This time zone is 7 hours behind G.M.T.
- Pacific Standard Time (PST): This time zone is 8 hours behind G.M.T. Los Angeles is located in this time zone.

Question 29.

Why is standard time more useful for a country than local time?

Answer:

A number of meridians pass through every country. If their local time is considered then the proper functioning of the national services like railways, airways, postal department in the country gets hindered. So, a country considers the time of its central meridian or the standard meridian as the standard time for the entire country. This is why standard time is more useful for a country than local time.

Question 30.

What is the Indian Standard Time?

Answer:

India, in the Eastern Hemisphere, has a vast longitudinal extent i.e., from 68° 7′ E to 97° 25′ E. Thirty meridians, each having their own local time, pass through this country. So, the local time of the meridian, 821° E, that passes through the city of Allahabad, which is more or less in the middle of the India, is followed as its Standard Time. This local time is known as the Indian Standard Time (I.S.T.).

Short Questions and Answers : (3 marks for each question)

Question 1.

How can we determine the longitude of a place?

Answer:

The longitude of a place can easily be determined with the following references-

1. With reference to time of any other longitude: We know that for a time difference of 4 minutes, we experience a 1° difference in longitude. So, if 4 minutes are added to the local time of a place we get the next longitude, at an interval of 1°, towards the east of that place. Similarly, if 4 minutes are subtracted from the local time of a place we get the next longitude, at an interval of 1°, towards the west of that place. Therefore, if the local times of any two places are known along with the longitude of any one place, the longitude of the other place can be easily calculated.

2. With reference to G.M.T.: G.M.T. is the local time of the 0° meridian passing through Greenwich near London. This is also known as the Universal Time. So, if the time difference of a place from the G.M.T. is known, the longitude can be easily calculated. Time is ahead for places due east and behind for the places due west of Prime Meridian. E.g., the Indian Standard Time is ahead by 5 hours 30 minutes than that of G.M.T. Therefore, the longitude of the Standard Meridian of India will be 82° 30′ E.

Question 2.

How does the angle of elevation of Hadley’s Octans help to determine latitudes?

Answer:

In ancient times, people used the Pole Star to determine North, Hadley’s Octans to determine South, the Morning Star to determine East in the morning and Evening Star to determine West in the evening. Later, with the advent of an instrument called sextant, things became easier. Sextant is used to determine the angle between a celestial object and the horizon. This angle is also known as the object’s altitude. The instrument has an in-built telescope and helps to determine the latitude of a place. For example, altitude of the Hadley’s Octans in the Southern Hemisphere near the equator is zero and thus equator is located at the 0° latitude. From equator, if we move 111.3 km to the south we reach the 1° S latitude, and the sextant also shows an altitude of 1° between Hadley’s Octans and the local horizon.

Question 3.

What do you mean by the Greenwich Mean Time?

Answer:

Greenwich Mean Time or G.M.T. is the local time of the 0° Meridian passing through Greenwich near London. As different countries have different standard times, it becomes difficult to carry out international communications. To avoid this problem, Greenwich Mean Time is followed across the globe. Therefore, G.M.T. is also known as the Universal Time. Countries located due east of the Prime Meridian are ahead of the GMT while those due west are behind GMT.

Question 4.

How was the International Date Line determined?

Answer:

To use a global time zone system with an International Date Line, the day and date have to be separated at some part on the earth by marking a terminal point. The suitable solution was provided in 1884 by the International Meridian Conference (IMC), held in Washington D.C., that was attended by representatives of 25 nations. The IMC selected the 180° meridian as this terminal point. The imaginary line of International Date Line was thus drawn that follows the 180° longitude mostly but deviates from its original position near the Aleutian Islands, the Fiji and Chatham Islands. The International Date Line acts as a dividing line between the dates of the Eastern and Western Hemispheres. It is according to this line, that calendar dates are changed.

Question 5.

Why do some countries have more than one standard time?

Answer:

Places situated on different meridians have different local times. A number of meridians pass through every country. If their local times are considered then the proper functioning of the administration and business gets hindered. So, to avoid such situation, the local time of a central meridian is taken as the standard time for the entire country. However, countries with a vast east-west extent face problems regarding time difference between its eastern and western parts. Too great a time difference between the extreme east and the extreme west, causes inconvenience and confusion. Therefore, these countries are divided into several time zones, each having its own standard time. For example, the USA is divided into 4 time zones while the Russian Federation has 11 time zones.

Question 6.

What do you mean by the Daylight Saving Time or DST?

Answer:

In the countries of the high latitudes, the difference between the duration of day and night is quite high with the changing seasons. Therefore, many countries started using Daylight Saving Time or DST (first proposed by Benjamin Franklin in 1784) to make better use of the natural daylight in the evenings. Many use it to reduce the amount of energy needed for artificial lighting during the evening hours. Many countries in the Northern Hemisphere- like the USA, Central America, Canada, Europe, Asia, North Africa, observe DST. Similarly, many countries in the Southern Hemisphere-like Australia, New Zealand, South America, South Africa also observe DST. Daylight Saving Time is in use between March and April and ends between September and November. This is because the countries return to Standard Time in the Northern Hemisphere and the reverse in Southern Hemisphere.

Question 7.

Write a brief note on Prime Meridian and International Date Line.

Answer:

The Prime Meridian is the imaginary line of longitude, considered to have a value of 0°, which passes through the Greenwich Observatory in London.

Special characteristics:

- Directly opposite to it is the 180° line of longitude or the International Date Line.
- This divides the earth into two equal hemispheres-east and west.
- As this passes over the Royal Observatory in Greenwich, London, it is called the Greenwich line.
- Determines the location and local time of any place.

The International Date Line is an imaginary line that follows the 180° longitude mostly but deviates from its original position over the landmasses.

Special characteristics:

1. A calendar date first starts and ends at this line.

2. When anyone crosses the International Date Line from east to west, he subtracts 1 day and similarly adds 1 day as he crosses it from west to east.

Question 8.

Into how many heat zones can the earth be divided on the basis of latitudes?

Answer:

The earth is divided into three heat zones on the basis of the angle at which the sunrays fall. These are as follows-

1. Torrid Zone: It extends from the equator (0°) to the Tropics (23 1/2° N. and S). Some important countries that come under this zone are-Brazil, Venezuela, Nigeria, Kenya, Ghana, Malaysia, Indonesia, England and such others.

2. Temperate Zone: It extends from the Tropics (23 1/2° N. and S) to the Arctic and Antarctic Circles (66 1/2° N. and S). Some important countries that come under this zone are-the United States of America, Chile, France, South Africa, New Zealand, England, Canada, Japan, Germany, Italy and such others.

3. Frigid Zone: It extends from the Arctic and Antarctic Circles (66 1/2° N. and S) to the Poles (90° N. and S). Some important countries that come under this zone are-Antarctica, Siberia, Alaska, Greenland, Northern Canada, Norway, and northern parts of Sweden.

Write the differences between the following –

Question 1.

Latitude and Parallels of latitude

Answer:

The differences between a latitude and parallels of latitude are as follows-

Points of difference | Lalitude | Parallels of latitude |

1. Definition | It is the angular distance of a place, north or south of the equator, measured in degrees. | These are imaginary lines drawn around earth, parallel to the equator. |

2. Characteristics | These are angular distances from the centre of the earth. | These are imaginary lines drawn around the earth. |

3. Method of construction | Places having same latitudinal degree, if joined by a single line, form the parallel. | Parallels join all the places having the same latitudinal degree. |

Question 2.

Longitude and Meridians of longitude

Answer:

The differences between a longitude and meridians of longitude are as follows-

Points of difference | Longitude | Meridians of longitude |

1. Definition | Angular distance of a place east or west of the Greenwich Meridian, measured in degrees, is known as the longitude. | A meridian is the half of an imaginary great circle on the surface of the earth, that ends at the geographical polesthe North Pole and the South Pole. |

2. Characteristics | These are angular distances from the centre of the earth. | These are imaginary lines drawn between the north and south poles. |

3. Method of construction | All the places having the same longitudinal degree, if joined by a single line, form the meridian. | It connects all the points of equal longitude. |

Question 3.

Latitude and Longitude

Answer:

The differences between latitude and longitude are as follows-

Points of difference | Lafitude | Longtude |

1. Definition | The angular distance of a place north or south of the equator, usually measured in degrees, is known as latitude. | The angular distance of a place east or west of the Greenwich meridian, usually measured in degrees, is known as longitude. |

2. Direction | Latitudes are drawn from east to west. | Longitudes are drawn from north to south. |

3. Shape and size | Latitudes are full circles and their size become smaller as we move from equator to the poles. | Longitudes are half circles and their size remains the same throughout. |

4. Total number | There are 181 latitudes in all, including the equator, when drawn at 1° interval. | There are 360 longitudes in all, when drawn at 1° interval. |

5. Measured from | Latitudes are measured on north or south of the equator. | Latitudes are measured on east or west of the Prime Meridian. |

6. Extension | Latitudes extend from the equator (0°) to the poles (90°) in either hemisphere. | Longitudes extend from the Prime Meridian (0°) to the 180° longitude in either hemisphere. (Note: 180° E and 180° W are the same line of longitude.) |

7. Hemispheres | Latitudes divide the earth into two hemispheres. | Longitudes divide the earth into Eastern and Western Hemispheres. |

8. Climatic characteristics | The climatic characteristics of various places lying on the same latitude are alike. | The climatic characteristics of various places lying on the same longitude are different. |

9. Local time | The local time of various places lying on the same latitude are different. | The local time of various places lying on the same longitude are alike. |

10. Use | The earth can be divided into heat zones on the basis of latitudes. | Local time of a place can be calculated on the basis of longitudes. |

Question 4.

Local time and Standard time

Answer:

The differences between local time and standard time are as follows-

Points of difference | Local Time | Standard Time |

1. Concept | The time of a place as determined when the sun is directly overhead the meridian passing through that place, is called local time. | The time in any country as standardised according to the local time at its Standard Meridian is called standard time. |

2. Number | Each longitude has a local time, which means that there are innumerable local times. | This is the central meridian of a country or a time zone. So only 1 standard time is there for a country or a time zone. |

3. Usage | Practical usage of this is not significant. | This is done primarily for convenience of administration and governance. |

Give reasons for the following :

Question 1.

The equator is known as Great Circle.

Answer:

When the centre of the circle and the centre of the globe are the same it becomes a Great Circle. There are several imaginary lines of latitude drawn over the earth’s surface, and out of those lines, the equator is known as the Great Circle, because-

- The great circle is the largest circle. It is not possible to draw a circle larger than the Great Circle over the earth’s surface.
- The centre of the earth and that of the Great Circle lies at the same point.
- If any circle is divided along the Great Circle, we get two equal halves.

Question 2.

Longitude and time are interrelated.

Answer:

Longitude and time are interrelated because –

1. Determination of mid-day and local time: Longitude helps in determining the time of mid-day of any area. The time of mid-day helps in determining the rest of the time of the day, because each and every longitude of the earth faces the sun at least once in 24 hours.

2. The difference between each 1° longitude and time is 4 minutes: The earth takes 24 hours to complete a rotation. So, the earth rotates 360° in 24 hours i.e., 360 / 24 = 15° or 1° in 4 minutes.

3. The time which lies in the longitude of the Eastern areas is always ahead: The earth rotates from West to the East, so the places in the East experience sunrise and sunset earlier than the places in the West.

So, the places located in the East are ahead in time than the places located in the West.

Question 3.

The difference of time between a place and its antipode is 12 hours.

Answer:

If any imaginary line from any point on the earth’s surface passes through the centre of the earth and touches the point opposite to the starting point, the latter is called the antipode of the former. So, an antipodal point is situated at the opposite longitude. The longitudinal difference between any place and its antipode point is 180°. So, we can mathematically prove thatWhen longitudinal difference is 1°, time difference is = 4 minutes

When longitudinal difference is 180°, time difference is = 180 × 4 minutes

= 720 × minutes = 12 × hours

Question 4.

Why is the 180° longitude is known as International Date Line?

Answer:

180° longitude is known as International Date Line because –

1. 180° longitude is the starting and ending point of the dates and time of the earth.

2. Since 180° longitude passes mostly over the water bodies, the time zones of the continents are not affected.

3. When the 180° longitudinal line is crossed from the western side of the Greenwich, the international date increases by a day. Again, when the 180° longitudinal line is crossed from the eastern side of the Greenwich, international date is decreased by a day.

Long Questions and Answers : (5 marks for each question)

Question 1.

What are meant by parallels of latitude? Discuss their properties and their uses. [1 + 2 + 2]

Answer:

The imaginary lines drawn around the earth parallel to the equator are known as the parallels of latitude. These are used to indicate the lines of latitude. These lines join all the places with the same latitudinal degree.

Properties:

- The paraliels of latitude are full circles and parallel to each other.
- As the value of the latitudes increase, the circumference of the parallels of latitude gradually decreases.
- At the poles, the distance around the earth is zero. Therefore, the poles appear to be dots.
- All places on the same parallel of latitude have the same latitudinal degree.
- Solar incidence changes with changing latitude. Accordingly, the climatic characteristics of the places also vary.
- The local time of various places lying on the same latitude are different.

Uses:

- The North-South position of a place can be determined by using the equator and the other latitudes as standard of measurement.
- The parallels of latitude are often used as the boundary of a country or a state. For instance, the 45° N parallel forms an approximate border between Quebec (Canada), and the states of New York and Vermont in the USA.
- The earth can be divided into different heat zones (Torrid zone, Temperate zone and Frigid zone) on the basis of latitudes.

Question 2.

How can you determine the latitude of a place geometrically? How can the latitude of a place in the Northern Hemisphere be determined using the elevation of the Pole Star? [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]

Answer:

Geometric determination of the latitude of a place: In the given Fig. 3.3, B denotes the earth’s centre, DC the equator, A the North Pole and P the Pole Star. N is a place in the Northern Hemisphere with MO as its horizon. Moreover, BQ is perpendicular to MO. As the Pole Star is located vertically above the North Pole, it will be visible at P’ position from N. Consequently, the angle of elevation of the North Star, as visible from N, would be ∠MNP ‘ and the latitudinal degree of N would be ∠NBC.

Figure 3.3: Geometric determination of latitude

Now, MNP’ + QNP’ = A right angle and, PBN + NBC = A right angle

Therefore, PBN + NBC = M MP’ + QNP’

Moreover, since BP and NP’ are parallel to each other, so PBN = QNP’

Hence, NBC = MNP’

Therefore, the angle of elevation of the Pole Star, as visible from N = the latitudinal degree of N.

Elevation of the Pole Star to determine the latitude of a place: In an open place-two poles, one taller than the other, were fixed. The smaller pole was fixed south of the taller one in such a way that the smaller pole, the taller pole to its north and the Pole Star as visible in the sky, were all in a straight line. Now, after measuring the exact distance between the poles on a white paper. the poles need to be drawn to the scale. Therefore, in the figure, YR and ZS are the two poles, with RS being the distance between the two. Now, Y and Z are joined and simultaneously, SR is extended so that these two meet at the point D and form an angle ∠ZDS. Hence, ∠YDR is the angle of elevation of the Pole Star and also the latitudinal degree. So, if the ∠YDR is measured with the help of a protractor, the latitude of the place can be determined.

Question 3.

What is meant by meridians of longitude? Discuss their properties and their uses. [1 + 2 + 2]

Answer:

In geography, a meridian is the half of an imaginary great circle on the surface of the earth, that ends at the geographical poles -the North Pole and the South Pole. It connects all the points of equal longitude. Each meridian is of equal length and is perpendicular to all the circles of latitude.

Properties:

- The meridians of longitude are all half circles.
- They are not parallel to each other.
- The distance between two consecutive meridians is the highest at the equator, and reduces gradually towards the poles.
- All the meridians are of equal length.
- All places on the same meridian have the same longitudinal degree.
- The climatic characteristics of the places on the same longitude vary drastically.
- The local time of various places lying on the same longitude are always the same.

Uses:

- The East-West position of a place can be determined by using the Prime Meridian and the other longitudes as standard of measure.
- The local time of any place on the surface of the earth can be calculated based on which longitude it is positioned.

Question 4.

Explain with examples how the location of a place can be determined using the lines of latitude and longitude. How does the local time change with changing lines of longitude? [3 + 2]

Answer:

Determination of location of a place with the help of Parallels of Latitude and Meridians of Longitude: The location of any place on the earth’s surface can be determined by using the lines of latitude and longitude. The Parallels of Latitude are full circles and run in an east-west direction. On the other hand, the Meridians of Longitude are half circles and run in a north-south direction. The combination of these two components form a graticule that specifies the position of any place on the earth. This is why both Parallels of Latitude and Meridians of Longitude are shown on the maps. To determine the exact location of a place, both are essential.

For example, location of the city of Kolkata is 22° 30′ N and 88° 30′ E. This statement explains the fact that Kolkata is located at the intersection point of 22° 30′ N latitude and 88° 30′ E longitude. The local time changes with change in longitude: The longitudes of the earth are half circular lines that extend from north to south. Since the earth rotates on its axis once every 24 hours, each longitude faces the sun directly once every 24 hours. When the sun is directly overhead any longitude, it is noon at that point. The local time at this longitude is measured with reference to noon at this point. Therefore, each line of longitude experiences noon only once every 24 hours and each longitude experiences it at different points of time. That is why local time changes with change in the longitude.

Figure 3.6: Determination of the location of a place with the help of latitudes and longitudes

Question 5.

What is the International Date Line? Explain the significance of the line. Why does the International Date Line not follow the 180° line of longitude throughout? [1 + 2 + 2]

Answer:

The International Date Line is an imaginary line that follows the 180° longitude. However, it deviates from its original position near the Aleutian Islands, the Fiji and Chatham Islands. The International Date Line acts as a divider between the dates of the eastern and western hemispheres. It is according to this line that the calendar date changes.

Significance: The earth takes 24 hours or 1440 minutes to complete one rotation of 360°. Therefore, for every 1° difference in longitude, we experience a time difference of 4 minutes. Moreover, since the earth rotates from west to east, the local time in the east is ahead of the local time in the west. So, if the local time is followed on a world tour, a lot of discrepancies can arise regarding the date and time of the places. This creates a lot of confusion and inconvenience for business purposes.

For example, both the 180° E and the 180° W are actually the same line, but the time difference as any aeroplane or ship crosses the line is calculated to be – 12 h + 12 h = 24 h or 1 day.

A suitable solution was provided in 1884 by the International Meridian Conference (IMC), held in Washington D.C., that was attended by representatives of 25 nations. The IMC selected the 180° meridian as the terminal point. The International Date Line acts as a divider between the dates of the Eastern and Western Hemispheres. It is according to this line, that calendar dates are changed. As anyone crosses the International Date Line from east to west, he subtracts 1 day (that is if it was Monday earlier, now it becomes Sunday for him) and adds 1 day (that is if it was Sunday earlier, now it becomes Monday for him) as he crosses it from west to east, to keep parity with the time and date of that place.

The International Date line does not follow the 180° line of longitude throughout: The International Date Line almost coincides with the 180° longitude but not completely. It zigzags to avoid crossing over any landmass. In the Northern Hemisphere, the International Date Line is displaced eastwards to avoid the Wrangel island as well as the Chukchi Peninsula on the Russian mainland, and then deviates west to avoid the Bering Sea and almost 7° to avoid Aleutian Islands. In the Southern Hemisphere, the International Date Line deviates almost 11° to avoid Fiji, Chatham and such other islands. This makes it convenient for all the people of Siberia to follow the standard time of Siberia, Aleutian Island to follow the Pacific Standard Time of the USA and Fiji, Tonga and Chatham to follow the standard time of New Zealand and avoid any kind of confusion.

Question 6.

Why is it necessary to determine the location of a place? How can the earth be divided into various heat zones? [2 + 3]

Answer:

Necessity of determining the location of a place:

- The exact location of the place on the surface of the earth can be determined.
- It helps to find the distance between any two or more places.
- The location of a place helps us to understand the explanation of any geographical research and study.
- The climatic characteristics of a place can be more or less surmised if the location of the place is known.

Heat zone: The rays of the sun fall at different angles at different places on the earth at different times of the year. The earth is divided into three heat zones on the basis of the angle at which the sunrays fall. These are as follows-

1. Torrid Zone: Extends from the Equator (0°) to the Tropic of Cancer (231° 2°) in the North and to the Tropic of Capricorn (231° 2°) in the South. Some important countries that come under this zone are-Brazil, Venezuela, Nigeria, Kenya, Ghana, Malaysia, Indonesia, England and such others.

2. Temperate Zone: Extends from the Tropics (231° N. and S) to the Arctic and Antarctic Circles (66 1/2° N. and S). Some countries that come under this zone are- United States of America, Chile, France, South Africa, New Zealand, England, Canada, Japan, Germany, Italy and several others.

3. Frigid Zone: Extends from the Arctic and Antarctic Circles (66 1/2° N. and S) to the Poles (90° N. and S). Some countries that come under this zone are-Antarctica, Siberia, Alaska, Greenland, northern Canada, Norway, and the northern parts of Sweden.

Question 7

What is meant by great circle? What is meant by antipode? [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]

Answer:

Great Circle:

Concept: A circle formed on the surface of a sphere by a plane that passes through the centre of the sphere is called a great circle. It is different from a general circle in which the intersection point of the sphere and a plane need not pass through the centre of the sphere. For instance, the equator is the only possible great circle among the lines of latitude on the surface of the earth, because equator alone fulfils the requirement to be called a great circle.

Properties:

- It is the largest possible circle that can be drawn on the surface of a sphere.
- An infinite number of great circles can be drawn on any sphere and any of the great circles always bisects the sphere.
- The centre of the great circle and that of the sphere will be the same.
- The arc of a great circle is the shortest distance between any two points on the surface of the sphere.

Uses: The arc of a great circle being the shortest distance between any two points on the surface of the sphere, the aeroplanes and ships try to follow these routes. This is what is popularly known as the Great Circle Route.

Antipode:

Concept: The antipode of a place is a point on the earth’s surface which is diametrically opposite to it. The two points which are antipodal to one another can be connected by a straight line running through the centre of the earth. For instance, the antipode of North Pole is the South Pole.

Properties:

- The time difference between a place and its antipode is 12 hours.
- The longitudinal difference between a place and its antipode is 180°.
- Though the angular value of a place and its antipode is the same, they are always located in the opposite hemispheres.

Examples: As depicted in the figure above, Kolkata is located at 22° 30′ N latitude and 88° 30′ E longitude. So the antipode of Kolkata would be located at 22° 30′ S latitude and (180° – 88° 30′) = 91° 30′ W longitude.

Significance:

- To ensure a fair circumnavigation following the great circle route, cressing a pair of antipodal points is inevitable. This is regardless of from where the traveller has started.
- Antipodes have contrary seasons at the same time.
- The length of day in a place is equal to the length of night at its antipode.

Question 8.

Discuss the important lines of latitude and longitude.

Answer:

The important lines of latitude are as follows-

The important lines of longitude are as follows-

Question 9.

1. The local time of places X and Y are Saturday 9 pm and Sunday 3 am respectively. The longitude of X is 90° W. Determine the longitude of Y.

2. What will be the time of I.S.T. when chronometer shows 12 noon? [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]

Answer:

1. Determination of the longitude of Y :

The local time of places X and Y are Saturday 9 pm and Sunday 3 am respectively. Therefore, the difference in local time between X and Y is –

(Saturday 9 pm – Sunday 3 am) i.e., [Saturday (24h – 21h = 3h) + Sunday 3h] = 6 h or 360 m.

Now, we know that for every 4 minutes’ time difference, longitudinal difference is 1°.

Therefore, for 360 minutes’ time difference, the longitudinal difference will be 360 ÷ 4 = 90°

Hence, the longitudinal difference between X and Y is 90°.

Since the local time of Y is ahead of the local time of X, this means that Y is located due east of X.

Therefore, longitude of Y is (90° – 90°) = 0°.

2. Determination of time of I.S.T:

The chronometer runs on the basis of Greenwich time. Therefore, if it is 12 noon according to chronometer, then it can be inferred that time at Greenwich or the Prime Meridian (0°) is also 12 noon. On the other hand, it is also known that the Standard Meridian of India is 82° 30′ E.

Hence, longitudinal difference between the Prime Meridian i.e., the G.M.T. and I.S.T. is(82° 30′-0°) = 82° 30′. Now the time difference for 82° 30′ longitudinal difference will be-

For every 1° longitudinal difference, time difference experienced is 4 minutes.

Therefore, for 82° longitudinal difference, time difference will be (82 × 4)=328 minutes.

Again, for every 1′ longitudinal difference, time difference experienced is 4 seconds.

Therefore, for 30′ longitudinal difference, time difference will be (30 × 4)=120 seconds or 2 minutes.

So, the total time difference between G.M.T. and I.S.T. becomes (328 + 2)=330 minutes or 5 h 30 m.

Since Standard Meridian of India is located due east of the Prime Meridian, so I.S.T. would be ahead of G.M.T.

Therefore, when it is 12 noon according to G.M.T., the time according to I.S.T. would be (12h + 5h 30 m) = 17: 30 hours or 5: 30 pm.

Question 10

1. The longitude of places A and B are 20° E and 35° E respectively. What will be the local time of B when it is Sunday 11 pm at A?

2. A news is broadcast at 8 am from Greenwich. What will be the longitude of the place that receives the broadcast at 2:30 pm? [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]

Answer:

1. Determination of the local time of the place B:

It is known that, the longitudes of A and B are 20° E and 35° E respectively.

Hence, the longitudinal difference between A and B is – (35°-20°) = 15°.

For every 1° longitudinal difference, the time difference experienced is 4 minutes.

Therefore, for 15° longitudinal difference, the time difference will be (15 × 4)=60 minutes or 1 hour.

Since B is located due east of A, so the time of B would be ahead of A.

Therefore, when it is 11 pm at A, the time at B would be (Sunday 11 pm+1 h) i.e., (23 h+ 1 h)=24 h or Monday 00:00.

2. Determination of the longitude of the unknown place: The news broadcast at 8 am from Greenwich (0°), is received at the unknown place at 2:30 pm, local time.

Therefore, the difference in local time between Greenwich and the unknown place is-

(2: 30 pm-8 am), i.e., (14 h 30 m-8 h)=6 h 30 m or 390 m.

Now, for every 4 m time difference the longitudinal difference is 1°.

Therefore, for 390 m time difference the longi-tudinal difference will be 390 ÷ 4 = 97° 30′.

As per the question, the time of the unknown place is ahead of Greenwich, so the unknown place would be located due east of Greenwich (0°). Therefore, the longitude of the unknown place would be (0° + 97° 30′)=97° or 97° 30′ E.

Question 11.

1. The captain of a ship notices that the local time at a port, where his ship has just reached, is showing 7:30 pm. But the Chronometer then shows the time 11:46 pm. What is the longitude of the port that the ship has reached?

2. How can the latitude be determined with reference to Hadley’s Octans? [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]

Answer:

1. Determination of the longitude of the port:

The chronometer runs on the basis of the Greenwich time.

When the ship reached the port at 11:46 pm according to Greenwich time, the local time of the port was 7:30 pm

Therefore, the time difference between these two places would be (11:46 pm – 7:30 pm) i.e., (23 h 46 m-19 h 30 m)=4 h 16 m or 256 m.

Now, for every 4 m time difference, the longitudinal difference is 1°.

Therefore, for 256 m time difference the longitudinal difference will be 256 ÷ 4 = 64°.

So, the longitudinal difference between Greenwich and the port is 64°.

As it is known that the time of the port is behind that of Greenwich, so the port would be located due west of Greenwich (0°). Therefore, the longitude of the port would be (64° – 0°) = 64° or 64° W.

2. Determination of a latitude with reference to Hadley’s Octans: Hadley’s Octans is a constellation of stars in the southern sky that is noteworthy as marking the geographical South Pole. In ancient times, people used the Pole Star to determine north and Hadley’s Octans to determine south. The Hadley’s Octans is visible in the night sky from all places in the Southern Hemisphere but its altitude is not the same at all places. The altitude changes with varying latitudes. The altitude of the Hadley’s Octans near the equator is zero and thus equator is measured as 0° latitude. From the equator, if we move 111.3 km to the south, we reach the 1° S latitude and the altitude of Hadley’s Octans at 1° S is measured to be 1°. In the same sequence, the angle of elevation of the Hadley’s Octans is measured to be 90° or exactly vertical at the South Pole. Therefore, with reference to the angle of elevation of the Hadley’s Octans from the horizon of a place, the latitude of the place can be easily determined.

Question 12.

1. New York is located at 74° W. What would be the time at New York when it is 11 am at Greenwich? 2. Determine the difference in local time of a place and its antipodal point.

Answer:

1. Determination of the local time at New York:

Now, the longitude of Greenwich is 0°.

Therefore, the longitudinal difference between Greenwich and New York is(74°-0°)=74°.

Now, for 1° longitudinal difference, time difference is 4 m.

So, for 74° longitudinal difference, time difference will be 74 × 4 = 296 m or 4 h 56 m.

As New York is located due west of Greenwich, the local time of New York will be behind Greenwich time.

Therefore, while it is 11 am at Greenwich, the time at New York would be (11 h – 4 h 56 m) = 6 h 04 m or 6: 04 am.

2. Determination of the difference in local time of a place and its antipodal point: The antipode of a point is a point on the earth’s surface which is diametrically opposite to it. So, the longitudinal difference between these two places is always 180°.

We know, for 1° longitudinal difference, time difference is 4 m.

So, for 180° longitudinal difference, time difference will be 180 × 4 = 720 m or 12 h. Therefore, the difference in local time of a place and its antipodal point is 12 hours.

Question 13.

(1) When it is 6: 30 am in Chennai, the time at New York is 8: 13 pm of the previous day. What is the longitude of New York, if the longitude of Chennai is 80° 15′ E ? 2 While on a voyage, a captain of a ship notices at 1 pm that the time shown in the chronometer is 6:30 pm Which longitude is the ship passing through at that time? [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]

Answer:

1. Determination of the longitude of New York:

When it is 6: 30 am in Chennai, the time in New York is 8: 13 pm of the previous day. Therefore, the difference in local time between Chennai and New York is (8:13 pm of previous day – 6: 30 am) or [(24 h-20 h 13 m) + 6 h 30 m] = 10 h 17 m or 617 m.

Now, for every 4 m time difference, the longitudinal time difference is 1°.

Therefore, for 617 m time difference, the longitudinal difference will be (617 ÷ 4) = 154° 15′.

So, the longitudinal difference between New York and Chennai is 154° 15′.

Now, since the local time of New York is behind the local time of Chennai, this implies that New York is located due west of Chennai.

Therefore, the longitude of New York is (154° 15′ – 80° 15′) = 74° or 74° W.

2. Determination of longitude of New York:

The chronometer runs on the basis of Greenwich time.

The time difference between Greenwich time and the unknown location of the ship is (6: 30 pm-1 pm) or (18 h 30 m-13 h) = 5 h 30 m or 330 m.

Now, for every 4 m time difference, the longitudinal difference is 1°.

Therefore, for 330 m time difference, the longitudinal difference will be 330 ÷ 4 = 82° 30′.

So, the longitudinal difference between Greenwich and the unknown location of the ship is 82° 30′.

As it is known that the time of the unknown location is behind that of Greenwich, so the unknown location would be located due west of Greenwich (0°). Therefore, the longitude of the unknown location would be (82° 30′-0°) = 82° or 82° 30′ W.

Question 14.

1. When the local time of Tripoli (13°. 12′ E) is 5 pm, the local time of an unknown city would be 7 am. What would be the longitude of this unknown city?

2. When the local time of Kolkata is 11:30 am., the local time of Tokyo is 2:51 pm. What would be the longitude of Tokyo? [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]

Answer:

1. Determination of the longitude of the unknown city:

The difference in local time between Greenwich and the unknown city is(5 pm-7 am) i.e., (17 h-7 h) = 10 h or 600 m. Now, for every 4 m time difference, the longitudinal difference is 1°.

Therefore, for 600 m time difference, the longitudinal difference will be 600 ÷ 4 = 150°.

As per the question, the time of the unknown city is behind that of Tripoli, so the unknown city would be located due west of Tripoli (13° 12′ E). Therefore, the longitude of the unknown place would be (150°-13° 12′) = 136° 48′ or 136° 48′ W.

2. Determination of the longitude of Tokyo:

The difference in local time between Kolkata and Tokyo is-

(2 : 51pm – 11 : 30am) i.e., (14h 51m – 1h 30m) = 3h or 21m or 201m.

Now, for every 4 m time difference, the longitudinal difference is 1°

Therefore, for 201 m time difference, the longitudinal difference will be 201 ÷ 4 = 50° 15′.

As per the question, the time in Tokyo is ahead of Kolkata, so Tokyo would be located due east of Kolkata (88° 30′ E). Therefore, the longitude of Tokyo would be (88° 30’+ 50° 15′) = 138° 45′ or 138° 45′ E.

Question 15.

What would be the local time of Dhaka (90° E), when it is 6 am in Seoul (127° 06’E)?

Answer:

Both Seoul and Dhaka are located in the Eastern Hemisphere.

The longitudinal difference between Seoul and Dhaka is (127° 06′-90°) = 37° 06′.

So, the difference in time between Seoul and Dhaka would be-

If, for every 1° longitudinal difference, time difference experienced is 4 minutes.

Therefore, for 37° longitudinal difference, time difference will be (37 × 4) = 148 minutes or 2h 28 m.

Again, for every 1 ‘ longitudinal difference, time difference experienced is 4 seconds.

Therefore, for 6 ‘ longitudinal difference, time difference will be (6 × 4) = 24 seconds.

So, the total time difference between Seoul and Dhaka becomes (2 h 28m + 24 seconds) = 2h 28 m 24 seconds.

Since Dhaka is located due west of Seoul, so the local time of Dhaka would be behind the local time of Seoul. Therefore, when it is 6 am in Seoul, the local time of Dhaka would be (6 h-2 h 28 m 24 seconds) = 3 h 31 m 36 seconds or 3:31:36 am.

Question 16.

If one travels along the equator, the change in local time can be accurately measured. Whereas, if we travel along any other lines of longitude from the equator to the poles, the change of seasons can easily be identified. Explain. (2) An important news broadcast in radio from New York at 12 noon, is heard at 8 pm in a certain place. What would be the longitude of that place? [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]

Answer:

1. Reasons for change in local time and season: The earth rotates around its axis once every 24 hours or 1 day. So if a traveller circumferences the entire globe along the equator, he has to cross all the lines of the longitude. It is known that, for every 1° longitudinal difference, time difference experienced is 4 minutes. Therefore, the traveller who travels along the equator experiences difference in time as he crosses each longitude.

On the other hand, as the earth is in the form of a sphere, the angle of incidence of the sun’s rays on the earth’s surface increases from the equator towards the poles and therefore the amount of heat received in a given area decreases in the same direction. The surface temperature is normally highest near the equator and lowest at the poles. Therefore, the traveller who travels along any line of longitude from the equator towards the poles experiences differences in season.

2. Determination of the longitude of the unknown place:

The important news broadcast in radio from New York at 12 noon, was heard at 8 pm in the unknown place.

So, the difference in local time between New York and the unknown place is ( 8 pm-12 noon) i.e., (20 h-12 h) = 8 h or 480 m.

Now, for every 4 m time difference, the longitudinal difference is 1°.

Therefore, for 480 m time difference, the longitudinal difference will be 480 ÷ 4=120°.

As per the question, the time of the unknown place is ahead of New York, so the unknown place would be located due east of New York (74° W). Therefore, the longitude of the unknown place would be (120°-74°)=46° or 46° E.

Question 17.

Greenwich Time Signal is received by a place at 4:32 pm G.M.T. time. What is the longitude of that place, if the time taken by the signal to reach that place from Greenwich is calculated to be 2 minutes?

Answer:

Determination of the longitude of the unknown place:

Greenwich Time Signal (2 minutes)

The Greenwich Time Signal from Greenwich at 12 noon, was heard at 4: 32 pm in the unknown place. The time taken by the time signal to reach that place from Greenwich is 2 minutes.

Therefore, the signal should have reached that place at (4 h 32 m-2 m) = 4h 30 m i.e., at 4:30 pm if the time lost in transmission is ignored.

So, the difference in local time between Greenwich and the unknown place is( 4: 30 pm-12 noon) i.e., (16 h 30 m-12 h) = 4 h 30 m or 270 m.

Now, for every 4 m time difference, the longitudinal difference is 1°.

Therefore, for 270 m time difference, the longitudinal difference will be 270 ÷ 4 = 67° 30′.

So, the longitudinal difference between Greenwich and the unknown place is 67° 30′.

As per the question, the time of the unknown place is ahead of Greenwich, so the unknown place would be located due east of Greenwich (0°). Therefore, the longitude of the unknown place would be (0°+ 67° 30′) = 67° 30′ or 67° 30′ E.

Question 18.

What would be the local time, day and date at Kolkata (88° 30′ E), while it is Wednesday 8:30 pm on December 31, 2014 at New York?

Answer:

Determination of the local time, day and date at Kolkata:

The longitudinal difference between New York and Kolkata is- (74° + 88° 30′) = 162° 30′.

Therefore, the difference in local time between New York and Kolkata would be-

Now, for 1° longitudinal difference time difference is 4 m.

So, for 162° longitudinal difference time difference will be 162 × 4 = 684 m.

Again, for every 1 ‘ longitudinal difference time difference experienced is 4 s.

Therefore, for 30′ longitudinal difference time difference will be (30 × 4)=120 s or 2 m.

So, the total time difference between New York and Kolkata becomes (648+2)=650 m or 10 h 50 m.

As Kolkata is located due east of New York, the local time of Kolkata will be ahead the New York time.

Therefore, while is Wednesday 8:30 pm on 31 December, 2014 at New York, the time at Kolkata would be (Wednesday 8:30 pm on 31 December, 2014 + 10 h 50m ) = Thursday 7:20 am on 1 January, 2015.

Question 19.

1. What would be the longitude of an unknown place that records 12 o’clock noon, while it is 4: 30 pm at Greenwich?

2. What would be the local time at Madrid (3° 42′ W), when it is 8 pm at Vienna (16° 20’ E) ? [2 \(\frac{1}{2}\) + 2 \(\frac{1}{2}\)]

Answer:

1. Determination of the longitude of the unknown place:

The difference in local time between Greenwich and the unknown place is( 4: 30 pm-12 noon) i.e., (16 h 30 m-12 h)= 4 h 30 m or 270 m.

Now, for every 4 m time difference the longitudinal difference is 1°.

Therefore, for 270 m time difference the longi- tudinal difference will be 270 ÷ 4=67° 30′.

So, the longitudinal difference between Greenwich and the unknown place is 67° 30′.

As per the question, the time of the unknown place is behind Greenwich, so the unknown place would be located due west of Greenwich (0°). Therefore, the longitude of the unknown place would be (67° 30′ – 0°)=67° 30′ or 67° 30′ W.

2. Determination of the local time at Madrid:

The longitudinal difference between Vienna and Madrid is-

(16° 20’+3° 42′) = 20° 02′.

Now, for 1° longitudinal difference time difference is 4 m.

So, for 20° longitudinal difference, time difference will be 20 × 4=80 m or 1 h 20 m.

Again, for every 1′ longitudinal difference, time difference experienced is 4 s.

Therefore, for 2′ longitudinal difference, time difference will be (2 × 4)= 8 s.

So, the total time difference between Vienna and Madrid becomes (1h 20 m+ 8 s)=1 h 20 m 8 s.

As Madrid is located due west of Vienna, the local time of Madrid will be behind Vienna time.

Therefore, while it is 8 pm at Vienna, the time at Madrid would be (20 h-1 h 20 m 8 s) =18 h 39 m 52 s or 6: 39: 52 pm.

Question 20

It takes 8 h by flight to reach London from Kolkata. At what time the flight would reach London, if it takes off for London at 8 pm on 31 December, 2014 as per I.S.T. time?

Answer:

Determination of the time and date when the flight will reach London:

The longitudinal difference between Kolkata and London is (82° 30′-0°)=82° 30′.

So, the difference in time between Kolkata and Greenwich would be-

If, for every 1° longitudinal difference, time difference experienced is 4 minutes.

Therefore, for 82° longitudinal difference, time difference will be (82 × 4) = 328 minutes.

Again, for every 1′ longitudinal difference, time difference experienced is 4 seconds.

Therefore, for 30′ longitudinal difference, time difference will be (30 × 4) = 120 seconds or 2 minutes.

So, the total time difference between London and Kolkata becomes (328 + 2) = 330 minutes or 5 h 30 m.

As London is located due west of Kolkata, the time at London would be behind Kolkata. Therefore, when it is 8 pm on 31 December, 2014 in Kolkata, the time at London would be (20 h-5 h 30 m) = 14: 30 hours or 2 : 30 pm same day and date.

Now, it takes 8 h by a flight to reach London from Kolkata.

So, the flight will reach at (14 h 30 m + 8 h) = 22 h 30 m or 10: 30 pm the same date and day i.e., December 31, 2014.

Question 21.

When it is 6:32 am in Chennai, the time at New York is 8: 15 pm the previous day. As Chennai is located at 80° 15′ E, where is New York located? (2) Why is the radio broadcast time difference between Kolkata (88° 30′ E) and Dhaka (89° E) 30 m even if the longitudinal difference between them is 30′ ? [2 \frac{1{2+2 \frac{1{2]

Answer :

1. Determination of the longitude of New York:

The local time of New York is 8: 15 pm and Chennai is 6:32 am at the same time.

So, the difference in local time between New York and Chennai is-

(Previous day 8:15 pm – 6:32 am) or [(24h20 h 15 m) + 6 h 32 m] = 10 h 17 m or 617 m.

Now, for every 4 m time difference, the longitudinal difference is 1°.

Therefore, for 617 m time difference, the longitudinal difference will be 617 ÷ 4 = 154° 15′.

As per the question, the time at New York is behind that of Chennai, so New York would be located due west of Chennai. Therefore, the longitude of New York would be (154°.15′ – 80° 15′) = 74° or 74° W.

2. Reasons for the difference in radio broadcast time between Kolkata and Dhaka: Longitudinal difference between Kolkata and Dhaka is 30′. Accordingly, the time difference between them should have been 2 m. But the difference in radio broadcast is 30 m. The reason behind this is, the time that the radio broadcast followed in Kolkata is according to the I.S.T. (82° 30′ E) and that in Dhaka is that of their standard meridian of 90° E.

The longitudinal difference between Kolkata and Dhaka is (90° – 82° 30′) = 7° 30′. So, the difference in time between Kolkata and Dhaka would be-

If, for every 1° longitudinal difference, time difference experienced is 4 minutes.

Therefore, for 7° longitudinal difference, time difference will be (7 × 4) = 28 m.

Again, for every 1 ‘ longitudinal difference, time difference experienced is 4 seconds. Therefore, for 30′ longitudinal difference, time difference will be (30 × 4) = 120 seconds or 2 minutes.

Therefore, the total time difference between London and Dhaka becomes (28 + 2) = 30 minutes.

Question 22.

Determine the antipodal point for Kolkata (22° 30′ N, 88° 30′ E). 2 What would be the day and date of the antipodal point of Kolkata, when it is Thursday, 1 March, 2012, 8 am? [2 + 3]

Answer :

1. The antipodal point of Kolkata: It is known that the longitudinal difference between a pair of antipodal points are always 180°. So, if longitude of Kolkata is 88° 30′ E, its antipode will be located at (180°-88° 30′) = 91° 30′ W.

The latitude of the antipode will also be located in the opposite hemisphere. The latitude of the antipode point of Kolkata would be 22° 30′ S.

Therefore, the antipodal point of Kolkata is located at 22° 30′ S, 91° 30’ W.

2. Determine the day, date and time of Kolkata’s antipodal point:

The time difference between a pair of antipodal points are always 12 h. So, if it is Thursday, March 1, 2012, 8 am in Kolkata, its antipode will have (Thursday, March 1, 2012, 8 am -12 h ) = Wednesday, 29 February, 2012, 8 pm. As 2012 is a leap year, February will have 29 days.

Question 23.

What do you mean by Daylight Saving Time or DST?

Answer:

I In the countries of the high latitudes, the difference between the duration of day and night is quite high with the changing seasons. For instance, in the Northern Hemisphere, at the 60° latitude, the length of daylight is 18 hours 27 minutes on the summer solstice day whereas on the winter solstice day it is 5 hours 33 minutes. Therefore, many countries started using Daylight Saving Time or DST to make better use of the natural daylight in the evenings and many use it to reduce the amount of energy needed for artificial lighting during the evening hours.

Though, Benjamin Franklin from the USA was the first to propose the DST concept in 1784, Germany was the first country to practically implement this practice in 1916. DST is now in use in over 70 countries. Today clocks are almost always set one hour back or ahead, but throughout history, there have been several variations. The beginning and end dates vary from one country to another. The European ‘Union adopted the ‘Summer Time’ period that was used in the United Kingdom for many years, where DST begins on the last Sunday in March and ends on the last Sunday in October.

Many countries in the Northern Hemispherelike the USA, Central America, Canada, all European nations, some Asian nations as well as some in northern Africa, observe DST. Similarly, many countries in the Southern Hemispherelike Australia, New Zealand, South America, southern Africa also observe DST. Daylight Saving Time is in use between March and April and ends between September and November as the countries return to Standard Time in the Northern Hemisphere and the reverse in Southern Hemisphere.