Question 1

Question 6Explain the meaning of the terms 'Solstice' and 'Equinox'.

Accepted Answer

The term 'Solstice' means an event occurring when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. It occurs on June 21 (Summer Solstice) and December 22 (Winter Solstice).The time when the Sun crosses the plane of the Earth's Equator making length of the day equal to length of night all over the earth, is known as 'Equinox'. It occurs on March 21 and September 23.

Question 2

Question 7What causes the formation of day and night? Explain with the help of a neat diagram.

Accepted Answer

The formation of the day and night is due to rotation of earth. While rotating, the part of earth facing the Sun has day and the other part has night. The Circle of Illumination is the imaginary line which shows clear demarcation between the phenomena of day and night on the Earth.

Question 3

Question 15Explain with the help of a diagram, the part played by the inclination of Earth's axis in causing day and night of varying duration, except at the Equator.

Accepted Answer

The effect of the inclined axis on the duration of day and night is that their duration differs as shown in the diagram below:At the Equator, place C would be at position C' after 12 hours.Distance CO = Distance OC'∴ Length of day = Length of night.On the Tropic of Cancer place B will be at B' after 12 hours.But distance BX is greater than B'X.∴ Days are longer than nights.On the Arctic Circle place A will be at position A' after 12 hours. AA' remains in continuous light in summer for six months.∴ Day of 24 hours near the North Pole in summer.Place D on the Tropic of Capricorn in the Southern Hemisphere will be at position D' after 12 hours.Distance DY (in light) is less than the distance D'Y (in darkness)∴ Days are shorter than nights.Place E on the Antarctic Circle remains in continuous darkness in winter.∴ Night for 24 hours near the South Pole in winter for six months.

Question 4

Question 19State the effect of speed of Earth's rotation.

Accepted Answer

Following are the effects of speed of Earth's rotation:All moving bodies on the Earth's surface, i.e. ocean currents and winds are deflected towards the right in the Northern Hemisphere and left in Southern Hemisphere.Cyclones and anti-cyclones are deflected causing atmospheric changes.It affects the pressure belts and movement of air on the surface of earth.The bulging of the air at the Equator and flattening at the poles is also due to rotation.

Question 5

Question 22What is an orbit?

Accepted Answer

A definite path or a curved trajectory in which a planet revolves around the Sun is called its orbit.

Question 6

Question 24State two effects of West to East rotation of the Earth.

Accepted Answer

Two effects of West to East rotation of the Earth are:The rotation of earth from West to East determines the direction in which the Sun, Moon and stars appear to rise and set.Ocean currents and winds are deflected towards right in the Northern Hemisphere and towards the left in the Southern Hemisphere. This is called Coriolis Effect.

Question 7

Question 25Explain the term 'Equinox'. When does it occur?

Accepted Answer

The time when the Sun crosses the plane of the Earth's Equator making length of the day equal to length of night all over the earth, is known as 'Equinox'. It occurs on March 21 and September 23.

Question 8

Question 10Assertion (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.Both A and R are true and R is the correct explanation of A.Both A and R are true but R does not explain A.A is true but R is false.A is false but R is true.

Accepted Answer

Both A and R are true and R is the correct explanation of A.Explanation — Centrifugal force is an apparent outward force that acts on a rotating object. It is always directed outward, i.e., away from the axis of rotation. The speed of rotation has created a centrifugal force resulting in a bulge in the middle portion of the earth and flattened top at the poles.

Question 9

Question 11Assertion (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.Both A and R are true and R is the correct explanation of A.Both A and R are true but R does not explain A.A is true but R is false.A is false but R is true.

Accepted Answer

Both A and R are true and R is the correct explanation of A.Explanation — The earth rotates on an inclined axis in an elliptical path around the sun. The earth's axis is inclined at an angle of 23.5° from the perpendicular to this plane of the elliptic. As a result of this, 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. For the remaining part of the year, the situation is reversed.

Question 10

Question 16Assertion (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.Both A and R are true and R is the correct explanation of A.Both A and R are true but R does not explain A.A is true but R is false.A is false but R is true.

Accepted Answer

A is false but R is true.Explanation — When the earth is closer to the sun, the gravitational pull makes the earth move faster than when it is away from the sun. Thus, the speed of revolution of the earth is not uniform.

Question 11

Question 23Assertion (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.Both A and R are true and R is the correct explanation of A.Both A and R are true but R does not explain A.A is true but R is false.A is false but R is true.

Accepted Answer

Both A and R are true and R is the correct explanation of A.Explanation — The twilight continues as long as sun is 18° below the horizon. In temperate regions, the angle at which the sun rises and sets is more slanted, so it takes longer to reach 18° below the horizon, hence longer dawn and dusk.

Question 12

Question 2Draw a diagram of the position of the Earth on December 22. Draw and name the Equator, Arctic Circle, and Antarctic Circle.

Accepted Answer

Below diagram shows the position of the Earth on December 22 with Equator, Arctic Circle, and Antarctic Circle labelled:

Question 13

Question 4With the help of a diagram show how the tilt of the Earth's axis and the revolution causes (i) seasons, (ii) variation in the length of day and night.

Accepted Answer

Below diagram shows the tilt of the Earth's axis and the revolution causing seasons and variation in the length of day and night:

Question 14

Question 5Draw self-explanatory diagram of Perihelion and Aphelion.

Accepted Answer

Below diagram shows Perihelion and Aphelion:

Question 15

Question 12The regions, near North Pole and South Pole, have six months of continuous day-light and darkness.

Accepted Answer

The Poles experience six-month day and six-month night due to the inclination of the earth's axis. Because of its tilted position each pole is inclined alternatively towards the Sun for six months resulting in continuous day and night.

Question 16

Question 9On which two days are the days and nights equal all over the world and why? What name do you give to these days?

Accepted Answer

The days and nights are equal all over the world on March 21st and September 23rd because the sun crosses the plane of the earth's equator making day and night of equal length.March 21st is known as Spring or Vernal Equinox and September 23rd is known as Autumnal equinox.

Question 17

Question 13Why 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?

Accepted Answer

Days and nights are equal at all places on earth on September 23 because on this date, the sun shines vertically over the equator, making day and night of equal length.It is autumn season in the northern hemisphere and spring season in the southern hemisphere.

Question 18

Question 14What is meant by Summer Solstice? When do we have Summer Solstice in the Northern Hemisphere?

Accepted Answer

On June 21, the northern hemisphere is tilted towards the sun and the sun is overhead at the Tropic of Cancer. So, the northern hemisphere enjoys the longest day. This day is called Summer Solstice.We have Summer Solstice in the Northern Hemisphere on June 21st.

Question 19

Question 17Briefly 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?

Accepted Answer

The cycle of seasons is determined by the change in the angle of the sun's rays hitting the earth's surface, which is caused by the earth's axial tilt of approximately 23.5 degrees. As the earth orbits the sun, different parts of the earth are tilted towards or away from the sun at different times of the year, resulting in the four seasons.Torrid zone receives almost vertical rays of the sun and temperate zone and frigid zone receive slanting rays of the sun.

Question 20

Question 18How is the duration of twilight influenced by seasons?

Accepted Answer

The duration of twilight is influenced by seasons because it is related to the angle at which the Earth's axis tilts towards the Sun, which changes as the Earth orbits around the Sun throughout the year.In summer, the Sun sets at a shallower angle, causing longer periods of twilight. The twilight period is defined as the time between sunset and when the Sun is 18° below the horizon. Since the angle of the Sun's descent is more gradual in summer, it takes longer for it to reach the 18° mark, resulting in longer periods of twilight.In winter, the Sun sets at a steeper angle, causing it to reach the 18° mark more quickly, resulting in shorter periods of twilight.

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