IB Physics

yr 13 - Revision of thermal physics

Internal energy

• The sum of the random distributions of kinetic and potential energies of all the molecules in the body.

Factors affecting internal energy

• Temperature - If the temperature of a system rises, the molecules travel more rapidly.

• Pressure- If the pressure changes - a change in potential energy and a change in internal energy

• State - Any change in state involves a change in the potential energy and a change in internal energy

Gas laws

• Boyle’s Law - p1V1 = p2V2 provided the temperature remains constant

• Pressure Law - p1/ T1    =     p2/T2 provided the volume of a gas is kept constant.

               

• Charles law - V1/ T1    =     V2/T2 provided the pressure of a gas is kept constant.

               

Ideal gas equation

• pV=NkT

• N - number of molecules

• k - Boltzmann constant

Multiple Choice

When energy is supplied to a substance, changes in the average molecular kinetic energy (E_k ) and the average molecular potential energy (E_p ) can occur. When energy is supplied to an ideal gas

• both E_k and E_p may increase

• E_k may increase

• E_p may increase

• E_k increases but E_p decreases

Multiple Choice

A sealed gas jar contains a mixture of different gases. At a given temperature, the mean kinetic energy of the molecules of each gas

• depends upon how much of each gas is present.

• is greater for the gas with less massive molecules.

• is greater for the gas with more massive molecules.

• is the same for each gas in the mixture.

Multiple Choice

An inflated balloon is considered to be a sphere having a volume of 8.2 × 10^–3 m³ in at a room temperature of 22 °C. Calculate the number of air molecules if the pressure of air in balloon = 1.1 × 10⁵ Pa

• 2.7 x 10²⁵

• 2.2 × 10²³

• 3.036 x 10²

• 2.2 x 10²⁴

Multiple Choice

Air is a mixture of mostly nitrogen and oxygen molecules. The mass of an oxygen molecule is slightly greater than the mass of a nitrogen molecule. On average, in a sample of air at a given temperature

• the nitrogen and oxygen molecules have the same speed

• the nitrogen molecules are travelling more slowly than the oxygen molecules

• the oxygen molecules are travelling more slowly than the nitrogen molecules.

• the molecules have relative speeds that depend upon the amount of each gas present.

SPECIFI HEAT CAPACITY

• Q = mCΔT

• C - Specific heat capacity

Multiple Choice

The heating element of an electric shower has a power of 6.0 kW. Water enters the shower at a temperature of 7.5 °C. Calculate the water flow rate required to give an output temperature of 37.5 °C. specific heat capacity of water = 4200 J kg^–1 K^–1

• 0.038 kgs^-1

• 0.1904 kgs^-1

• 0.0400

• 0.0476 kgs^-1