Unit 5: Physics from Creation to Collapse
Thermal Energy
Term Definition
- Sum of total kinetic energy and potential energy (1) of
Internal Energy (2)
molecules/atoms (1)
What happens to the internal energy, kinetic energy and potential energy when water at
100 ℃ turns into steam at 100 ℃ . (1 mark)
- Both the internal energy and the potential energy of the molecules increase (1)
State an assumption that has to be made when calculating internal energy. (1 mark)
- No energy transferred to surroundings/all energy transferred from tea used to heat milk (1)
A sample of gas is made of a mixture of nitrogen and oxygen. What is the average
molecular kinetic energy of the molecules at a given temperature. (1 mark)
- The same for molecules of both gases (1)
Suggest why a pre-warmed teapot may allow more flavor to be extracted. (1 mark)
- Water molecules will have a greater average K.E./less energy transferred to teapot (1)
The calculated specific heat capacity of stainless steel is larger than the actual value.
Explain the difference. (2 marks)
- Energy is transferred to the surroundings (1) so the energy gained by the teapot has been
overestimated (1)
How is the average kinetic energy of the molecules in an ideal gas related to temperature?
(1 mark)
- Average kinetic energy of the molecules in an ideal gas is directly proportional to the
absolute temperature (1)
Explain why the internal energy of the air can be taken as the total kinetic energy of the
molecules of the air. (2 marks)
- Internal energy is the sum of kinetic and potential energy of the molecules in the air (1)
- The molecules in an ideal gas have no potential energy (1)
Discuss what happens to the energy of the copper atoms before and during the melting
process. (2 marks)
- Whilst copper is being heated to melting point, energy supplied is transformed into KE of
atoms (1)
- At melting point, no change in KE of atoms/energy supplied is transformed into PE of atoms
(1)
Explain one precaution that the student should take when carrying out the experiment to
make the energy calculated as accurate as possible. (2 marks)
- Water should be stirred (1) so water is all at the same temperature (1)
- No draughts (1) so that all the energy from the crisp is transferred to the test tube (1)
,- Keep crisp close to test tube (1) to reduce the heat dissipated to surroundings
Two metal spheres (lead and steel) of the same size are heated to a temperature of 100
℃ and are then placed on a sheet of paraffin wax. The steel sphere melted straight
through the wax but the lead sphere only partially melted. Explain this observation. (2
marks)
- Heat energy is transferred from the sphere to the wax (1)
- Idea that the lead sphere has insufficient energy for melting the wax e.g. the lead sphere
transfers less heat energy than the steel sphere (1)
Air is a mixture of mainly nitrogen and oxygen. Oxygen molecules are more massive than
nitrogen molecules. Nitrogen accounts for about 80% of the molecules in a given sample
of air. Compare the mean square speed of oxygen to nitrogen molecules in a sample of air.
(2 marks)
- Oxygen molecules are more massive than nitrogen molecules and have a lower mean
square speed than the nitrogen molecules (1) because ½m<c2> is the same for each type of
molecule (1)
Explain why the nitrogen molecules would account for 80% of the pressure exerted by the
air. (3 marks)
- Both gases occupy the same volume and are at the same temperature (1)
- As pressure p = NkT/V then p ∝ N the number of molecules (1)
- The contribution to pressure exerted by each gas is determined by the number of
molecules (1)
For a black-body radiator, how is the frequency at which maximum radiation of energy
occur related to temperature? (1 mark)
- Proportional to T
The relative masses of oxygen and hydrogen molecules are 32 and 2 respectively. For any
given temperature, what is the ratio of Orms/Hrms given by? (1 mark)
- 1/4 (1)
1 3
In the equation m<c2> = kT, what does the term <c2> represent? (1 mark)
2 2
- The mean square speed of the molecules (1)
Explain how graph such as this provide evidence for an absolute zero of temperature. (2
marks)
,- Extrapolating the line backwards (1)
- The volume occupied by a gas will be zero at a particular temperature (1)
An article states that the internal energy of the air in the balloon could become zero if the
temperature of the gas become low enough. Explain what is meant by the internal energy
of the air and discuss whether the statement is correct. (4 marks)
- Internal energy is the sum of molecular kinetic and potential energies (1)
- In an ideal gas the molecules have only kinetic energy/the molecules do not have potential
energy (1)
3
- Since Ek = kT (1) therefore if the gas reached absolute zero, then the KE of the
2
molecules would be zero and so the statement is correct/if air is identified as not being
ideal, then allow idea that molecules would still have potential energy at 0 K, and so
statement is incorrect (1)
As the gas cloud contracts, the internal energy of the system increases. Explain how
energy conservation applies to the system during this period of contraction. (2 marks)
- Gravitational potential energy decreases (1) as cloud collapses
- Decrease in gravitational potential energy equals increase in internal energy (1)
A physics student plans to repeat an experiment but using a thermometer with a precision
of 0.25K, where in the first experiment the temperature difference is 0.6. Discuss the
extent to which she will be able to draw a valid conclusion from her measurements with
this thermometer. (3 marks)
- Uncertainty in temperature readings is ± 0.25 ℃ (1)
- Uncertainty in temperature difference may be ± 0.5 ℃ (1)
- Comparison of 0.5 ℃ /0.25 ℃ with 0.6 ℃ /attempt at calculation of percentage
uncertainty with statement that it is too large (1)
- Reference to assumptions about conditions top and bottom (1)
Describe an experiment you could carry out to measure the specific heat capacity of a
metal, assuming that you have a number of metal washers which can be heated to a
known temperature in a Bunsen flame and plunged into a container of water. State the
measurements that you would need to make and give the theoretical basis of the
calculation that you would carry out. What assumption would you make in calculating the
specific heat capacity of the metal? (4 marks)
- Assumption: That no energy is transferred to the surroundings/energy required to raise
temperature of container is negligible (1)
- Measure the mass of the washers and water (1) using a balance
- Measure the temperature of the water before and after the washers are plunged into the
water (1)
- Equate thermal energy lost by steel to the energy gained by water (1)
- Use a standard value for the specific heat capacity of the water/specific heat capacity of
water is known (1)
The graph shows the thermal energy transferred from the chocolate to the surroundings.
Explain the shape of the graph when it plateaus on the cooling curve. (2 marks)
, - Temperature is staying constant although energy is still being transferred from the
chocolate (1)
- The potential energy of the chocolate molecules decreases (1) resulting in a decrease in
internal energy
A bright spot is made when the ball is made in contact with the bat. Suggest and explain a
reason why using silicone tape may reduce the chances of a bright spot being produced. (2
marks)
- Smaller temperature increase (1) at the point of impact
- The silicone tape may be a better thermal conductor/have a higher specific heat capacity
(1)
The graph shows the rate at which thermal energy is transferred from the chocolate to the
surroundings. During the last 100s of cooling the temperature fell at a lower rate than
during the first 100s of cooling. Suggest why this is the case. (2 marks)
- Lower rate of temperature fall due to larger specific heat capacity (1) because thermal
energy is transferred to the surroundings at the same rate (1)
Or
- Solid is nearer to temperature of surroundings than the liquid (1) so rate of energy transfer
to surroundings must be less (1)
Calculate the temperature of the gas inside the tennis ball at the instant the tennis ball is
stationary during impact with the ground. (2 marks)
- p1V1/T1 = p2V2/T2 (1)
- T2 = 299.4K (1)
Explain how the change in total kinetic energy will affect the bounce height of the tennis
ball. (2 marks)
Thermal Energy
Term Definition
- Sum of total kinetic energy and potential energy (1) of
Internal Energy (2)
molecules/atoms (1)
What happens to the internal energy, kinetic energy and potential energy when water at
100 ℃ turns into steam at 100 ℃ . (1 mark)
- Both the internal energy and the potential energy of the molecules increase (1)
State an assumption that has to be made when calculating internal energy. (1 mark)
- No energy transferred to surroundings/all energy transferred from tea used to heat milk (1)
A sample of gas is made of a mixture of nitrogen and oxygen. What is the average
molecular kinetic energy of the molecules at a given temperature. (1 mark)
- The same for molecules of both gases (1)
Suggest why a pre-warmed teapot may allow more flavor to be extracted. (1 mark)
- Water molecules will have a greater average K.E./less energy transferred to teapot (1)
The calculated specific heat capacity of stainless steel is larger than the actual value.
Explain the difference. (2 marks)
- Energy is transferred to the surroundings (1) so the energy gained by the teapot has been
overestimated (1)
How is the average kinetic energy of the molecules in an ideal gas related to temperature?
(1 mark)
- Average kinetic energy of the molecules in an ideal gas is directly proportional to the
absolute temperature (1)
Explain why the internal energy of the air can be taken as the total kinetic energy of the
molecules of the air. (2 marks)
- Internal energy is the sum of kinetic and potential energy of the molecules in the air (1)
- The molecules in an ideal gas have no potential energy (1)
Discuss what happens to the energy of the copper atoms before and during the melting
process. (2 marks)
- Whilst copper is being heated to melting point, energy supplied is transformed into KE of
atoms (1)
- At melting point, no change in KE of atoms/energy supplied is transformed into PE of atoms
(1)
Explain one precaution that the student should take when carrying out the experiment to
make the energy calculated as accurate as possible. (2 marks)
- Water should be stirred (1) so water is all at the same temperature (1)
- No draughts (1) so that all the energy from the crisp is transferred to the test tube (1)
,- Keep crisp close to test tube (1) to reduce the heat dissipated to surroundings
Two metal spheres (lead and steel) of the same size are heated to a temperature of 100
℃ and are then placed on a sheet of paraffin wax. The steel sphere melted straight
through the wax but the lead sphere only partially melted. Explain this observation. (2
marks)
- Heat energy is transferred from the sphere to the wax (1)
- Idea that the lead sphere has insufficient energy for melting the wax e.g. the lead sphere
transfers less heat energy than the steel sphere (1)
Air is a mixture of mainly nitrogen and oxygen. Oxygen molecules are more massive than
nitrogen molecules. Nitrogen accounts for about 80% of the molecules in a given sample
of air. Compare the mean square speed of oxygen to nitrogen molecules in a sample of air.
(2 marks)
- Oxygen molecules are more massive than nitrogen molecules and have a lower mean
square speed than the nitrogen molecules (1) because ½m<c2> is the same for each type of
molecule (1)
Explain why the nitrogen molecules would account for 80% of the pressure exerted by the
air. (3 marks)
- Both gases occupy the same volume and are at the same temperature (1)
- As pressure p = NkT/V then p ∝ N the number of molecules (1)
- The contribution to pressure exerted by each gas is determined by the number of
molecules (1)
For a black-body radiator, how is the frequency at which maximum radiation of energy
occur related to temperature? (1 mark)
- Proportional to T
The relative masses of oxygen and hydrogen molecules are 32 and 2 respectively. For any
given temperature, what is the ratio of Orms/Hrms given by? (1 mark)
- 1/4 (1)
1 3
In the equation m<c2> = kT, what does the term <c2> represent? (1 mark)
2 2
- The mean square speed of the molecules (1)
Explain how graph such as this provide evidence for an absolute zero of temperature. (2
marks)
,- Extrapolating the line backwards (1)
- The volume occupied by a gas will be zero at a particular temperature (1)
An article states that the internal energy of the air in the balloon could become zero if the
temperature of the gas become low enough. Explain what is meant by the internal energy
of the air and discuss whether the statement is correct. (4 marks)
- Internal energy is the sum of molecular kinetic and potential energies (1)
- In an ideal gas the molecules have only kinetic energy/the molecules do not have potential
energy (1)
3
- Since Ek = kT (1) therefore if the gas reached absolute zero, then the KE of the
2
molecules would be zero and so the statement is correct/if air is identified as not being
ideal, then allow idea that molecules would still have potential energy at 0 K, and so
statement is incorrect (1)
As the gas cloud contracts, the internal energy of the system increases. Explain how
energy conservation applies to the system during this period of contraction. (2 marks)
- Gravitational potential energy decreases (1) as cloud collapses
- Decrease in gravitational potential energy equals increase in internal energy (1)
A physics student plans to repeat an experiment but using a thermometer with a precision
of 0.25K, where in the first experiment the temperature difference is 0.6. Discuss the
extent to which she will be able to draw a valid conclusion from her measurements with
this thermometer. (3 marks)
- Uncertainty in temperature readings is ± 0.25 ℃ (1)
- Uncertainty in temperature difference may be ± 0.5 ℃ (1)
- Comparison of 0.5 ℃ /0.25 ℃ with 0.6 ℃ /attempt at calculation of percentage
uncertainty with statement that it is too large (1)
- Reference to assumptions about conditions top and bottom (1)
Describe an experiment you could carry out to measure the specific heat capacity of a
metal, assuming that you have a number of metal washers which can be heated to a
known temperature in a Bunsen flame and plunged into a container of water. State the
measurements that you would need to make and give the theoretical basis of the
calculation that you would carry out. What assumption would you make in calculating the
specific heat capacity of the metal? (4 marks)
- Assumption: That no energy is transferred to the surroundings/energy required to raise
temperature of container is negligible (1)
- Measure the mass of the washers and water (1) using a balance
- Measure the temperature of the water before and after the washers are plunged into the
water (1)
- Equate thermal energy lost by steel to the energy gained by water (1)
- Use a standard value for the specific heat capacity of the water/specific heat capacity of
water is known (1)
The graph shows the thermal energy transferred from the chocolate to the surroundings.
Explain the shape of the graph when it plateaus on the cooling curve. (2 marks)
, - Temperature is staying constant although energy is still being transferred from the
chocolate (1)
- The potential energy of the chocolate molecules decreases (1) resulting in a decrease in
internal energy
A bright spot is made when the ball is made in contact with the bat. Suggest and explain a
reason why using silicone tape may reduce the chances of a bright spot being produced. (2
marks)
- Smaller temperature increase (1) at the point of impact
- The silicone tape may be a better thermal conductor/have a higher specific heat capacity
(1)
The graph shows the rate at which thermal energy is transferred from the chocolate to the
surroundings. During the last 100s of cooling the temperature fell at a lower rate than
during the first 100s of cooling. Suggest why this is the case. (2 marks)
- Lower rate of temperature fall due to larger specific heat capacity (1) because thermal
energy is transferred to the surroundings at the same rate (1)
Or
- Solid is nearer to temperature of surroundings than the liquid (1) so rate of energy transfer
to surroundings must be less (1)
Calculate the temperature of the gas inside the tennis ball at the instant the tennis ball is
stationary during impact with the ground. (2 marks)
- p1V1/T1 = p2V2/T2 (1)
- T2 = 299.4K (1)
Explain how the change in total kinetic energy will affect the bounce height of the tennis
ball. (2 marks)
