Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).

Assertion (A): Sensible heating of air increases the humidity of air.
Reason (R): Process of sensible heating is represented on the psychrometric chart by a straight horizontal line.

In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

"Sensible" processes mean change in temperature only with constant absolute moisture.
This translates to a horizontal line on the psychrometric chart.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Sensible heating refers to the addition of heat energy to air which results in an increase in dry-bulb temperature without changing the absolute moisture content (specific humidity) of the air.

Step 3: Detailed Explanation:
1.

Assertion (A): During sensible heating, the absolute amount of water vapor in the air remains completely constant.
Since the moisture mass is unchanged, the specific humidity remains constant, while the relative humidity actually decreases.
Therefore, sensible heating does not increase the humidity, making Assertion (A) false.
2.

Reason (R): On a standard psychrometric chart, specific humidity (moisture ratio) is plotted on the vertical y-axis, and dry-bulb temperature is on the horizontal x-axis.
Because specific humidity remains constant during sensible heating, the process follows a path parallel to the x-axis, which is a straight horizontal line moving from left to right. Thus, Reason (R) is true.

Step 4: Final Answer:
The correct option is 4, which corresponds to (A) is false but (R) is true.