Which of the following are the factors that cause variation in the amount of insolation on the Earth? 1. Rotation of the earth on its axis 2. Length of the day 3. Distribution of land and water on the earth Select the answer using the code given below:
- (a)1 only
- (b)1 and 2 only
- (c)2 and 3 only
- (d)1, 2 and 3
Correct — B, 1 and 2 only. The amount of insolation (incoming solar radiation) actually received at a place varies with a defined set of factors, and two of the three listed qualify: statement 1, the rotation of the earth on its axis, which changes the angle at which the sun's rays strike a place through the day; and statement 2, the length of the day, which sets how many hours a place is exposed to the sun. Statement 3, the distribution of land and water, is not among the standard factors governing the amount of insolation received — the recognised list is the rotation of the earth on its axis, the angle of the sun's rays, the length of the day, the transparency of the atmosphere and the configuration of land. So only 1 and 2 are correct.
- (a)1 only — It drops the length of the day, yet how long a place is exposed to the sun clearly affects the insolation it receives, so statement 2 also belongs.
- (c)2 and 3 only — It includes the distribution of land and water (not a listed factor) and omits the rotation of the earth on its axis, which is a genuine factor.
- (d)1, 2 and 3 — It adds the distribution of land and water, which is not one of the standard factors affecting the amount of insolation received.
Insolation is the incoming solar radiation received at the Earth's surface. The amount received at a place is not fixed — it varies with the rotation of the earth on its axis, the angle of inclination of the sun's rays (which depends on latitude and season), the length of the day, the transparency of the atmosphere, and the configuration of the land (its aspect). The angle of the sun's rays and the length of the day are the most important controls, which is why the tropics receive far more insolation than the poles.
The question mixes two genuine factors with one plausible-sounding distractor. The distribution of land and water strongly influences temperature and climate, but it is not listed among the factors that determine how much solar radiation actually arrives at a place; keeping that distinction is the key.
- Insolation is the incoming solar radiation received at the Earth's surface.
- The recognised factors affecting the amount received are: rotation of the earth on its axis, angle of the sun's rays, length of the day, transparency of the atmosphere and configuration of land.
- The angle of the sun's rays and the length of the day give the tropics much more insolation than the poles.
- The distribution of land and water strongly affects temperature and climate, but is not on the standard insolation-factor list.
Only items 1 and 2 are recognised insolation factors, so the answer is 1 and 2 only — option (b).
- Do not confuse factors that affect the AMOUNT of insolation received with factors that affect temperature (where land-water distribution does matter).
- Rotation and day length are both genuine insolation controls; the land-water distractor is the odd one out.
Usually asked by mixing real insolation factors (angle of rays, day length, rotation) with a temperature-control factor slipped in as a distractor.
No directly related past PYQ was found.
- practice — not a real PYQ
Which one of the following is the single most important factor determining the amount of insolation received at a place?
- (a)The colour of the soil
- (b)The angle of inclination of the sun's rays
- (c)The distribution of land and water
- (d)The direction of ocean currents
Answer(b) The angle of inclination of the sun's rays — a higher sun angle concentrates radiation over a smaller area.
- practice — not a real PYQ
The tropics receive more insolation than the poles mainly because at the poles:
- (a)the sun's rays are more slanting and pass through more atmosphere
- (b)the atmosphere is thicker with ozone
- (c)there is more land than water
- (d)the earth rotates faster
Answer(a) the sun's rays are more slanting and pass through more atmosphere, spreading and weakening the radiation.