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Question

How can one determine the relative humidity on a particular day at a given place?

This question was previously asked in
CDS 2 2024 Maths Question Paper (01-Sep-2024)
The correct answer is

If both temperature and absolute humidity are, given

Understanding how to determine relative humidity is crucial for meteorology and various environmental studies. Relative humidity tells us how much moisture is in the air compared to the maximum it could hold at that specific temperature. Let's explore how we can find this value for a particular day at a given place.

Factors Required to Determine Relative Humidity

To accurately calculate the relative humidity, we need two key pieces of information about the atmospheric conditions:

  • The amount of water vapor currently present in the air.
  • The temperature of the air.

Let's break down why each is essential:

The Role of Absolute Humidity

Absolute humidity refers to the actual mass of water vapor present in a specific volume of air (e.g., grams per cubic meter, g/m³). This tells us the 'current load' of moisture in the air. Without knowing the actual amount of moisture, we cannot compare it to the air's capacity.

The Importance of Temperature

Air's ability to hold water vapor is highly dependent on its temperature. Warmer air can hold significantly more water vapor than cooler air. Therefore, to know the *maximum* amount of water vapor the air can possibly hold (the saturation point), we must know the current temperature. The saturation point changes with temperature.

Calculating Relative Humidity

Relative humidity is defined as the ratio of the actual amount of water vapor in the air to the maximum amount the air could hold at the current temperature, expressed as a percentage.

The formula used is:

\(\text{Relative Humidity (RH)} = \left( \frac{\text{Absolute Humidity}}{\text{Saturation Humidity at the given Temperature}} \right) \times 100\%\)

From this formula, it's clear that we need both the 'Absolute Humidity' (the actual moisture) and the 'Saturation Humidity' (which is determined by the temperature) to calculate the relative humidity.

Analysis of Options for Determining Relative Humidity

Let's analyze the given options based on our understanding:

  • Option 1: If temperature is given
    This is insufficient. Knowing the temperature only tells us the air's capacity to hold moisture, not how much moisture is actually present.
  • Option 2: If absolute humidity is given
    This is also insufficient. Knowing the actual moisture content (absolute humidity) isn't enough unless we also know the air's capacity to hold moisture, which depends on temperature.
  • Option 3: If both temperature and absolute humidity are given
    This option provides both necessary components: the actual amount of water vapor (absolute humidity) and the air's capacity to hold vapor (determined by temperature). This allows for the calculation of relative humidity.
  • Option 4: If percentage of absolute humidity is given
    The term 'percentage of absolute humidity' is not standard in this context. Absolute humidity is a measure of concentration, not a percentage relative to anything else. Relative humidity is the percentage measure that requires comparison with the saturation point determined by temperature.

Conclusion

Therefore, the correct way to determine the relative humidity on a particular day at a given place is by having information about both the current moisture content (absolute humidity) and the air's saturation capacity, which is dependent on the temperature.

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