# Physics Questions and Answers – Thermal Properties of Matter – Ideal-Gas Equation and Absolute Temperature

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This set of Physics Multiple Choice Questions and Answers for Class 11 focuses on “Thermal Properties of Matter – Ideal-Gas Equation and Absolute Temperature”.

1. Boyle’s and Charle’s law are obeyed by low density gases only. True or False?
a) True
b) False

Explanation: Boyle’s and Charle’s law are used to arrive at the ideal gas law. And the ideal gas law is based on the assumptions of kinetic theory of gases, which are only valid for low density gases. For eg: the assumption that molecules exert no forces on each other can only be considered for low density.

2. Boyle’s law and Charle’s law together form which law?
a) PV/T = constant
b) PV2/T = constant
c) PV = constant
d) V/T = constant

Explanation: Boyle’s law states that P ∝ 1/V.
Charle’s law states that V ∝ T.
From this we can say that
V ∝ T/P OR PV/T = constant.
Note that this is the ideal gas law.

3. Why can any low density gas be used in a constant volume gas thermometer?
a) All low density gases show the same expansion behaviour
b) They are easy to handle
c) Their pressure variation is proportional to square of the change in temperature
d) The given statement is not true

Explanation: It has been experimentally shown that low density gases show similar expansion behaviour. If we keep the gas’s volume constant pressure increases monotonically with increasing temperature. Hence, we can use any low density gas for a constant volume gas thermometer.

4. For a constant volume gas thermometer select the correct statement.
a) It doesn’t use mercury for pressure measurement
b) We actually measure the pressure at constant volume and the scale is calibrated to give the temperature reading
c) Any high density gas can be used
d) Pressure ∝ Temp2

Explanation: A constant volume gas thermometer has a mercury manometer connected to a gas bulb. With increase in temperature of the bulb, its volume is kept constant by external methods and the pressure of gas increases. The temperature scale is defined as a function of this pressure. (T = kP, where k is a constant).

5. What is absolute zero?
a) It is the minimum temperature that has been achieved
b) It is the lowest temperature of air
c) It is -273K
d) It is the temperature at which an ideal gas will have zero pressure, assuming it stays a gas

Explanation: Absolute zero has been defined as the temperature at which an ideal gas would have zero pressure, assuming it remains a gas till then. The temperature value is obtained by extrapolating the graph of Pressure vs Temperature till the straight line cuts the temperature axis. This gives us a value of -273.15°C. Note that this temperature hasn’t been achieved yet.

6. What is considered as zero point on the Kelvin scale?
a) -273.15K
b) -273.15°C
c) 0°C
d) -273.15°C

Explanation: Zero point on the kelvin scale is absolute zero point.
This corresponds to the temperature of -273.15°C.
Also note that the kelvin scale and celsius scale have the same size of unit,
so K = 273.15 + °C.

7. What is the value of gas constant?
a) 8.314 kJ mol-1K-1
b) 8.314 L atm mol-1K-1
c) 0.0821 L atm mol-1K-1
d) It is equal to the constant in PV/T = constant

Explanation: The value of universal gas constant is 0.0821 L atm mol-1K-1.
Or it is 8.314 J mol-1K-1.
The constant in PV/T = constant depends on the number of moles taken.

8. In a constant volume gas thermometer, the pressure of liquid, at a temperature of 27°C, being measured corresponds to 50cm of mercury. If the temperature increases by 20K, find the pressure.
a) 53.33cm
b) 87.03cm
c) 65.33cm
d) 97.03cm

Explanation: For a constant volume gas thermometer, P/T = constant.
P1/T1 = P2/T2
∴ P2 = P1/T1 * T2 = 50/300 * 320 = 53.33cm.

Sanfoundry Global Education & Learning Series – Physics – Class 11. 