AQA A-level Thermal Physics

• m/8

• m/2

• 2m

• 8m

A sample P of an ideal gas contains 1 mol at an absolute temperature T.

A second sample Q of an ideal gas contains  2/3 mol at an absolute temperature 2T.

The total molecular kinetic energy of P is E.

What is the total molecular kinetic energy of Q?

• 2/3 E

• 3/4 E

• 4/3 E

• 3/2 E

An ideal gas is contained in a cubical box of side length a. The gas has N molecules each of mass m.

What is the pressure exerted by the gas on the walls of the box?

 

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At a certain temperature, the root-mean-square speed of the molecules of a fixed volume of an ideal gas is c. The temperature of the gas is changed so that the pressure is halved. The root-mean-square speed of the molecules becomes 

• c/4

• c/2

• 2c

The composition of a carbon dioxide (CO₂) molecule is one atom of  and two atoms of .

What is the number of molecules of CO₂ in 2.2 kg of the gas?

A student measures the power of a microwave oven. He places 200 g of water at 23 °C into the microwave and heats it on full power for 1 minute. When he removes it, the temperature of the water is 79 °C.

The specific heat capacity of water is 4200 J kg^–1 K^–1.

What is the average rate at which thermal energy is gained by the water?

 

• 780W

• 840W

• 1.1kW

• 4.6kW

A continuous stream of water falls through a vertical distance of 100 m.

Assume no thermal energy is transferred to the surroundings.

The specific heat capacity of water is 4200 J kg^–1 K^–1.

What is the temperature difference of the water between the top and bottom of the waterfall?

• 0.023K

• 0.23K

• 2.3K

• 4.3K

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A transparent illuminated box contains small smoke particles and air.

The smoke particles are observed to move randomly when viewed through a microscope.

What is the cause of this observation of Brownian motion?

• Smoke particles gaining kinetic energy by the absorption of light.

• Collisions between smoke particles and air molecules

• Smoke particles moving in convection currents caused by the air being heated by the light.

• The smoke particles moving randomly due to their temperature.

The average mass of an air molecule is 4.8 × 10^–26 kg

What is the mean square speed of an air molecule at 750 K?

 

• 4.3x10⁵m²s^-2

• 6.5x10⁵m²s^-2

• 8.7x10⁵m²s^-2