Question

The gas thermometers are more sensitive than liquid thermometers because gases
A)expand more than liquid.
B)are easily obtained.
C)are much lighter.
D)do not easily change their states.

Answer 1

Hint: The working of a thermometer is based on the principle of thermal expansion.

Complete step by step answer.
Step 1: Define thermal expansion.
Most substances, be it liquids, gases, or solids, expand on heating and contract on cooling.
Heating and cooling refer to a change in temperature. Thus, a change in the temperature of a substance causes a change in its dimensions.
Thermal expansion is the increase in the dimensions of a body when it is heated.
If there is an expansion of length, it is called linear expansion.
If there is an expansion of the area, it is called area expansion.
If there is an expansion of volume, it is called volume expansion.
The working of thermometers is based on the principle of thermal expansion.
Step 2: Explain the working of gas thermometers and liquid thermometers.
Both the gas thermometer and the liquid thermometer work based on the principle of thermal expansion.
A gas thermometer consists of a long thin glass tube filled with air and a rubber stopper with mercury sealed inside it. This glass tube is then placed in an open tube through which liquid or gas freely passes. (The pressure of the gas is kept constant). Now, as the temperature of the glass tube increases, the air expands leading the mercury to move along the tube. The temperature change can be read off of a calibrated scale of temperature on the glass tube that tracks this movement of mercury.
A liquid thermometer consists of a glass tube partially filled with some liquid. When the temperature around the bulb of the thermometer increases, the liquid in the tube expands causing the liquid to rise along the tube. The temperature change can be read off of a calibrated scale of temperature on the glass tube that tracks this rise of liquid. Mercury or alcohol is used as the liquid in the tube.
Step 3: Explain why gas thermometers are more sensitive than liquid thermometers.
Compared to liquids, the molecules in a gas are further apart from each other. Thus on heating, the molecules move faster than the molecules in a liquid. As a result, the increase in the volume of a gas will also be more than that of a liquid. Thus gases expand more than liquids, i.e., gas will expand more than liquids for the same tiny change in temperature. Hence, gas thermometers are more sensitive than liquid thermometers.
Therefore, the correct option is A) gases expand more than liquids.

Note: Solids, liquids and gases expand on heating. This expansion does not suggest that the atoms themselves expand. Instead, an expansion of volume occurs.