Rotation and Revolution - Questions & Answers
I. Choose the correct option:1. Which of the following is true about the rotation of the earth?
(a) The earth completes one rotation in 23:56:4.09 hrs
(b) The earth's axis passes through the poles
(c) The speed of rotation increases as we move towards the equator
(d) All of the above.
Answer: (d) All of the above.
2. See the above figure. What is the value of angle A?
(a) 0°
(b) 23½°
(c) 66½°
(d) 90°
Answer: (c) 66½°
3. An apparent outward force that acts on a rotating object:
(a) Centrifugal Force
(b) Sunset Effect
(c) Coriolis Effect
(d) Rotational Effect
Answer: (a) Centrifugal Force
4. Assertion (A): Rotation is the spinning of the earth on its axis from west to east once in 24 hours.
Reason (R): The earth is always tilted in the same direction as it moves round the sun.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true but R does not explain A.
5. Assertion (A): The winds and ocean currents move clockwise and are deflected to the right in the Northern Hemisphere.
Reason (R): Coriolis Effect refers to the force experienced by any object moving over the surface of a rotating body such as the earth.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
6. What is the shape of the path of the earth around the sun?
(a) Oval path
(b) Spherical path
(c) Elliptic
(d) Coriolis
Answer: (c) Elliptic
7. Which of the following is correct?
(a) Aphelion : earth is closest to the sun
(b) Aphelion : earth is farthest from the sun
(c) Aphelion : moon is closest to the earth
(d) Aphelion : the equator is closest to the sun.
Answer: (b) Aphelion : earth is farthest from the sun
8. What is the time difference between two consecutive lines of longitude?
(a) 7½ minutes
(b) 4 minutes
(c) 1 minute
(d) 3 minutes
Answer: (b) 4 minutes
9. Which of the following is true about the revolution of the earth around the sun?
(a) It results in the cycle of seasons
(b) The direction of motion is the same as rotation
(c) The speed is not uniform
(d) All of the above.
Answer: (d) All of the above.
10. Assertion (A): A bulge in the middle portion of the earth and flattened top at the poles.
Reason (R): Centrifugal force always directed outward, i.e., away from the axis of rotation.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
11. Assertion (A): In the course of the earth's movement around the sun, the North Pole remains inclined towards the sun for a part of the year while the South Pole is tilted away from it.
Reason (R): The earth rotates on an inclined axis in an elliptical path around the sun.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
12. Which of the following is true about the perihelion position of the earth?
(a) It is farthest from the sun.
(b) It occurs on 3 January.
(c) The speed of revolution is the least.
(d) All of the above.
Answer: (b) It occurs on 3 January.
13. The lighted part of the earth is called the (b) Circle of Illumination
(a) Circle of Light
(b) Circle of Illumination
(c) Circle of Solstice
(d) Circle of Equinox
14. Perihelion: 147.4 million km :: (a) Aphelion : 152 million km
(a) Aphelion
(b) Equinox
(c) Solstice
(d) All of the above.
15. Which of the following is true about the aphelion?
(a) Occurs on 4 July.
(b) Summer in northern hemisphere
(c) Speed of revolution is maximum
(d) All of the above.
Answer: (a) Occurs on 4 July.
16. Assertion (A): The speed of revolution of the earth is uniform.
Reason (R): When the earth is closer to the sun, the gravitational pull makes the earth move faster than when it is away from the sun.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (d) A is false but R is true.
17. Solstice : Summer/Winter :: (b) Equinox : Spring/Autumn
(a) Solstice
(b) Equinox
(c) Vernal
(d) None of the above.
18. Name the phenomenon when the regions beyond the Arctic Circle experience 24 hours daylight.
(a) Daylight sun
(b) Midnight sun
(c) Arctic sun
(d) Regional sun
Answer: (b) Midnight sun
19. The period of diffused light between sunset and complete darkness is called
(a) dawn
(b) dusk
(c) twilight
(d) Both (b) and (c)
Answer: (d) Both (b) and (c)
20. The duration of twilight:
(a) increases to the poles
(b) might last for as much as 7 weeks at the poles
(c) is as long as the sun is 18° below the horizon
(d) all of the above.
Answer: (d) all of the above.
21. Assertion (A): Phenomena of dawn and dusk is experienced more in temperate regions.
Reason (R): The twilight continues as long as sun is 18° below the horizon.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
1. What is meant by the inclination of earth's axis? At what angle is the earth's axis inclined?
Answer: The Earth's axis is an imaginary line passing through its centre on which it rotates. It is always tilted in the same direction, which is known as the inclination of the earth's axis. It is inclined at an angle of 23½° from the vertical, or 66½° with the plane of the Earth's orbit.
2. Name the two chief motions of the earth.
Answer: The two chief motions of the earth are Rotation and Revolution.
3. Describe two characteristics of rotation.
Answer: 1. The earth completes one rotation from west to east on its axis in roughly 24 hours. 2. The speed of the earth's rotation is highest at the Equator (1670 km per hour) and decreases to zero towards the poles.
4. Mention any two possible consequences if the axis of the earth was vertical instead of inclined.
Answer: 1. The length of day and night would have been exactly equal at all places on the earth. 2. There would be no seasons on the earth.
5. State one reason why we do not feel the motions of the earth.
Answer: We do not feel the motions of the earth because the force of gravity keeps everything attached to the earth, keeping all objects at rest with reference to the motions of the earth (in accordance with Newton's First Law of Motion).
6. What is an elliptic?
Answer: An elliptic refers to the oval-shaped path (elliptical orbit) along which the earth revolves around the sun.
7. State two chief characteristics of the revolution of the earth.
Answer: 1. The earth revolves round the sun in an elliptical orbit at an average speed of 29.8 kilometres per second. 2. It takes 365 days, 5 hours, 48 minutes and 45.51 seconds to make one complete revolution.
8. What do you understand by perihelion and aphelion?
Answer: Perihelion is the position when the earth is closest to the sun in its orbit (occurring around January 3). Aphelion is the position when the earth is farthest from the sun in its orbit (occurring around July 4).
9. On which two days are the days and nights equal all over the world and why? What name do you give to these days?
Answer: Days and nights are equal all over the world on March 21 and September 23. This is because on these dates, the sun shines vertically over the Equator. These days are called Equinoxes (Spring/Vernal Equinox and Autumnal Equinox).
10. Which is the longest and which is the shortest day in the Northern Hemisphere and why?
Answer: The longest day in the Northern Hemisphere is June 21 because the North Pole is tilted directly towards the sun (Summer Solstice). The shortest day is December 22 because the North Pole is tilted away from the sun (Winter Solstice).
11. On which dates does the sun shine vertically overhead at (a) Equator, (b) Tropic of Cancer, (c) Tropic of Capricorn?
Answer: (a) Equator: March 21 and September 23. (b) Tropic of Cancer: June 21. (c) Tropic of Capricorn: December 22.
12. Why is noon hotter than morning?
Answer: At noon, the sun is high in the sky and its rays fall almost vertically, concentrating a large amount of heat over a small area. In the morning, the sun's rays are slanting (oblique) and spread over a larger area, resulting in less concentrated heat.
13. Why are days and nights equal at all places on earth on September 23? What are the seasons in the Northern and the Southern Hemispheres on this date?
Answer: Days and nights are equal because the sun is shining vertically overhead at the Equator. On this date, it is Autumn in the Northern Hemisphere and Spring in the Southern Hemisphere.
14. What is meant by Summer Solstice? When do we have Summer Solstice in the Northern Hemisphere?
Answer: Summer Solstice is the time when the sun reaches its highest point in the sky at noon, shining vertically over the Tropic of Cancer, resulting in the longest day of the year. In the Northern Hemisphere, we have the Summer Solstice on June 21.
15. What is meant by Equinox?
Answer: Equinox is derived from Latin words meaning 'equal' and 'night'. It refers to the time when the sun crosses the plane of the earth's Equator, making night and day of equal length across the globe.
16. What will be the duration of daylight on March 21st at 23°30'N and 66°30'S latitudes? Give reason.
Answer: The duration of daylight will be 12 hours at both latitudes. The reason is that on March 21st (Equinox), the sun shines vertically over the Equator, making days and nights equal (12 hours each) everywhere on earth.
17. Briefly describe the cycle of seasons with the change in inclination of the sun's rays. Which temperature zone receives almost vertical rays of the sun and which zones receive slanting rays?
Answer: As the earth revolves on its tilted axis, the angle of the sun's rays changes, causing seasons. When a hemisphere is tilted towards the sun, it receives direct vertical rays (summer); when tilted away, it receives oblique/slanting rays (winter). The Torrid Zone receives almost vertical rays. The Temperate and Frigid Zones receive slanting rays.
18. How is the duration of twilight influenced by seasons?
Answer: The duration of twilight is longer during summer and winter and varies based on latitude. As one moves away from the Equator towards the poles, the sun rises and sets in a more oblique path, which makes the period of diffused light (twilight) last much longer, extending for weeks in polar regions depending on the season.
19. How has the phenomenon of the 'Midnight Sun' come about?
Answer: The phenomenon occurs because of the tilted axis of the earth. During summer in the Northern Hemisphere, the region beyond the Arctic Circle remains continuously in sunlight (tilted towards the sun) and experiences 24 hours of daylight, known as the 'Midnight Sun'.
20. Mention one effect of seasons in low and high latitudes.
Answer: In low latitudes (near the Equator), the variation in the length of day and night is minimal and seasons are less distinct. In high latitudes, the effect is extreme, leading to a massive contrast in seasons such as months of continuous daylight in summer and continuous darkness in winter.
21. Draw a well labelled diagram to show changes in the altitude of the midday sun at different times of the year.
Answer: [Students are required to draw the diagram based on textbook references illustrating the cycle of seasons and sun's rays on the Tropics and Equator.]
22. Your family had gone to London during your summer break. Your sister was surprised that it was daylight at 9:00 pm. How did you explain the phenomenon to her?
Answer: I would explain that London is located at a high latitude in the Northern Hemisphere. During our summer break (June), the Northern Hemisphere is tilted towards the sun. Because of this tilt and the latitude, days become extremely long, resulting in daylight lingering well into the evening, even at 9:00 pm.
23. Your penfriend from New Zealand has come to Agra to welcome the New Year. He is surprised that it is winters in Agra. What did you tell him?
Answer: I would tell him that New Zealand is located in the Southern Hemisphere, which is tilted towards the sun during New Year (December/January), so they experience summer. Agra is in the Northern Hemisphere, which is tilted away from the sun during this time, resulting in winter. Therefore, the seasons are opposite.
(i) Rotation and Revolution.
Answer: Rotation is the spinning of the earth on its axis from west to east, taking about 24 hours to complete, and it is responsible for day and night. Revolution is the movement of the earth around the sun in an elliptical orbit, taking about 365 1/4 days, and it is responsible for the cycle of seasons.
(ii) Vertical and Slanting Rays.
Answer: Vertical Rays fall straight, concentrating their heat over a smaller area, leading to high temperatures (found in the Torrid Zone). Slanting Rays fall obliquely, spreading the same amount of heat over a larger area, resulting in moderate or low temperatures (found in Temperate and Frigid zones).
(iii) Equinox and Solstice.
Answer: Equinox refers to the time when the sun crosses the Equator, making day and night equal all over the world (March 21 and September 23). Solstice refers to the time when the sun reaches its highest or lowest point in the sky at noon (over the Tropics), resulting in the longest or shortest days (June 21 and December 22).
1. (a) What is meant by rotation of the earth? State three effects of the rotation of the earth.
Answer: Rotation is the spinning of the earth on its axis from west to east once in 24 hours. Three effects are:
1. Occurrence of Day and Night.
2. Sunrise and Sunset (apparent movement of the sun from east to west).
3. The Coriolis Effect (deflection of winds and ocean currents).
(b) What is the effect of the inclined axis of the earth on day and night?
Answer: The inclined axis causes variations in the length of day and night across different latitudes. If the axis were vertical, days and nights would always be 12 hours everywhere. Because it is tilted, daylight duration increases in the hemisphere tilted towards the sun and decreases in the one tilted away.
(c) Give a geographical reason for each of the following:
(i) Kuala Lumpur rotates faster on the earth's axis than London.
Answer: The speed of earth's rotation is maximum at the Equator (where circumference is widest) and decreases towards the poles. Kuala Lumpur is situated closer to the Equator than London, so its rotational speed is faster.
(ii) We always see the sun rising in the east.
Answer: The earth rotates on its axis from west to east. As a result of this direction of spin, places in the east experience sunlight first, creating the apparent effect of the sun rising in the east.
(iii) Norway is called the Land of the Midnight Sun.
Answer: Norway is located at a high latitude near the Arctic Circle. During summer in the Northern Hemisphere, the region is tilted towards the sun and experiences continuous daylight for 24 hours, so the sun is visible even at midnight.
(d) Draw a well labelled diagram to show inclination of the earth on its axis.
Answer: [Students are expected to draw a diagram showing the Earth's axis inclined at 23½° to the vertical and 66½° to the orbital plane.]
2. (a) Describe how the duration of sunlight changes from the Equator to the Poles with respect to the angle of incidence during the solstices.
Answer: During solstices, the duration of sunlight is exactly 12 hours at the Equator. As one moves towards the pole of the hemisphere that is tilted towards the sun, daylight duration increases, becoming 24 hours at the polar circle and lasting for months at the pole. Conversely, moving towards the pole in the hemisphere tilted away from the sun, daylight duration decreases to 0 hours.
(b) Describe how seasons are made and reversed between the Northern and Southern Hemispheres.
Answer: Seasons are caused by the earth's revolution around the sun combined with the tilt of its axis. For half the year, the Northern Hemisphere is tilted towards the sun, experiencing summer, while the Southern Hemisphere is tilted away, experiencing winter. After six months, as the earth moves to the opposite side of its orbit, the tilt causes the Southern Hemisphere to face the sun (summer) and the Northern Hemisphere to face away (winter), reversing the seasons.
(c) Give a geographical reason for each of the following:
(i) The length of day and night is not equal at all places on the earth.
Answer: Because the earth's axis is inclined at an angle of 66½° to the plane of its orbit, different latitudes receive varying amounts of sunlight throughout the year.
(ii) The period of twilight and dawn increases polewards.
Answer: As one moves from the Equator towards the poles, the apparent path of the sun rising and setting becomes more oblique. Therefore, the sun takes a longer time to traverse the zone 18° below the horizon, increasing the duration of dawn and twilight.
(iii) In New Zealand Christmas is celebrated in summer.
Answer: New Zealand is situated in the Southern Hemisphere. During December, the Southern Hemisphere is tilted towards the sun, experiencing the summer season. Thus, Christmas falls in summer there.
(d) Draw a well labelled diagram to show the tilt of the earth's axis and how the revolution causes seasons and variation in the length of day and night.
Answer: [Students must refer to the textbook diagram illustrating the earth's elliptical orbit, marked with solstices and equinoxes, showing the tilted axis.]
1. Imagine the earth stops its rotation on its axis. What would be its impact on the inhabitants of the earth? Give examples to support your answer.
Answer: If rotation stopped, the side facing the sun would experience perpetual daylight and extreme, scorching heat. The side facing away would be in perpetual darkness and freezing cold. The massive temperature difference would cause devastating weather systems, and life as we know it would likely be destroyed.
2. You travel for winter vacation to Australia from India. What type of climate will be there in Australia? Give reasons to support your answer.
Answer: Australia will have a hot summer climate. India is in the Northern Hemisphere (experiencing winter), while Australia is in the Southern Hemisphere. When the Northern Hemisphere is tilted away from the sun, the Southern Hemisphere is tilted towards the sun, resulting in summer in Australia.
3. On June 21, your uncle who lives in New York experiences summer, whereas your cousin who lives in Jakarta, experiences winter. Give reasons to support your answer.
Answer: New York is in the Northern Hemisphere, which is tilted towards the sun on June 21, receiving direct vertical rays and experiencing the Summer Solstice. Jakarta is in the Southern Hemisphere, which is tilted away from the sun on this date, receiving slanting rays and thus experiencing winter.
1. With the help of a Power Point Presentation show
(i) change of seasons in the Northern Hemisphere.
(ii) the apparent path of the sun from the Equator to North Pole.
Answer: [This is a practical presentation activity for the student.]
2. Draw a diagram to show the winter solstice and answer the following questions.
(i) Name the correct date depicted in your diagram.
Answer: December 22.
(ii) Name the latitude where the sun is shining vertically overhead.
Answer: Tropic of Capricorn (23½° S).
(iii) Name the part of the globe where there is night on this date.
Answer: The entire region from the Arctic Circle (66½° N) to the North Pole (90° N).
(iv) Name the latitude on which length of the day will be 24 hours.
Answer: Antarctic Circle (66½° S) to South Pole (90° S).
(v) Give the date when the earth will be directly opposite to the above position.
Answer: June 21.
(vi) What will be the vertical position of the sun on that date?
Answer: Vertically overhead the Tropic of Cancer (23½° N).
(vii) What is the effect of the inclination of the earth upon the length of day and night?
Answer: The inclination causes unequal lengths of day and night. It makes days longer in the hemisphere tilted towards the sun and shorter in the hemisphere tilted away.
(viii) What will be the probable length of day and night on that date?
Answer: On June 21, the Northern Hemisphere will experience its longest day and shortest night, while the Southern Hemisphere will experience its shortest day and longest night. At the Equator, it will be 12 hours day and 12 hours night.