Which of the following statements regarding humidity is/are correct? 1. It is a ratio between the actual amount of water vapour present in the atmosphere and the maximum amount it can hold at a given temperature. 2. When the relative humidity is high, more water evaporates from the skin. 3. Higher the air temperature lower the relative humidity of the air. Select the answer using the code given below:
- (a)1 only
- (b)2 and 3 only
- (c)1 and 3 only
- (d)1, 2 and 3
Correct — C, statements 1 and 3 only. Relative humidity is the ratio of the actual amount of water vapour in the air to the maximum amount the air could hold at that temperature, usually shown as a percentage; statement 1 is this definition and is true. Statement 2 is false — when relative humidity is high the air is already close to saturation, so it can accept little more moisture and evaporation from the skin slows down rather than speeds up, which is exactly why sweat fails to dry and a humid day feels stifling. Statement 3 is true — because warmer air can hold more water vapour, a given amount of moisture makes up a smaller fraction of the higher capacity, so relative humidity falls as temperature rises. With 1 and 3 correct and 2 wrong, the answer is (c).
- (a)1 only — Drops the true statement 3 — a rise in air temperature does lower the relative humidity for a fixed vapour content, because warmer air can hold more.
- (b)2 and 3 only — Keeps the false statement 2 and drops the true definition in statement 1. High relative humidity slows evaporation from the skin, it does not increase it.
- (d)1, 2 and 3 — Includes statement 2, which is wrong — evaporation from the skin is reduced, not increased, when relative humidity is high.
Humidity is the amount of water vapour in the air. Relative humidity expresses that amount as a percentage of the maximum the air could hold at its current temperature — so it depends on both the vapour present and the temperature. Because a warmer parcel can hold more vapour, changing the temperature alone changes the relative humidity even if no moisture is added or removed.
The trap is statement 2, which sounds plausible but reverses the physics of evaporation. Evaporation is driven by the difference between the moisture in the air and saturation; when relative humidity is high that gap is small, so evaporation from wet skin slows and cooling is poor. This is the everyday experience that humid heat feels worse than dry heat at the same temperature.
- Relative humidity is the ratio of actual water vapour present to the maximum the air can hold at that temperature, expressed as a percentage.
- Warm air can hold more water vapour than cold air, so raising the temperature of a parcel lowers its relative humidity if the vapour content is unchanged.
- High relative humidity slows evaporation from the skin because the air is near saturation, reducing the body's evaporative cooling.
- Relative humidity reaches 100 per cent at the dew point, the temperature at which the air becomes saturated and condensation begins.
- Assuming high humidity speeds up evaporation and cooling — it does the opposite, which is why humid heat feels worse.
- Confusing relative humidity (temperature-dependent percentage) with absolute or specific humidity (actual mass of vapour).
Asked as a statement-code question that mixes the correct definition with a reversed claim about evaporation and a true temperature effect.
No directly related past PYQ was found.
- practice — not a real PYQ
The temperature at which the air becomes saturated and relative humidity reaches 100 per cent is the:
- (a)boiling point
- (b)dew point
- (c)critical point
- (d)lapse point
Answer(b) dew point — the temperature at which the air is saturated with water vapour and condensation begins.
- practice — not a real PYQ
If an air parcel is warmed with no change in its water-vapour content, its relative humidity will:
- (a)increase
- (b)decrease
- (c)stay the same
- (d)become zero
Answer(b) decrease — warmer air can hold more vapour, so the same amount of moisture is a smaller fraction of the higher capacity.