Critical Thinking Items

What are the necessary conditions for energy transfer by heat to occur between two bodies through the process of conduction?

1. They should be at the same temperature, and they should be in thermal contact.
2. They should be at the same temperature, and they should not be in thermal contact.
3. They should be at different temperatures, and they should be in thermal contact.
4. They should be at different temperatures, and they should not be in thermal contact.

Oil is heated in a pan on a hot plate. The pan is in thermal equilibrium with the hot plate and also with the oil. The temperature of the hot plate is 150 °C . What is the temperature of the oil?

1. 160 °C
2. 150 °C
3. 140 °C
4. 130 °C

Air is pumped into a car tire, causing its temperature to increase. In another tire, the temperature increase is due to exposure to the sun. Is it possible to tell what caused the temperature increase in each tire? Explain your answer.

1. No, because it is a chemical change, and the cause of that change does not matter; the final state of both systems are the same.
2. Although the final state of each system is identical, the source is different in each case.
3. No, because the changes in energy for both systems are the same, and the cause of that change does not matter; the state of each system is identical.
4. Yes, the changes in the energy for both systems are the same, but the causes of that change are different, so the states of each system are not identical.

How does the transfer of energy from the sun help plants?

1. Plants absorb solar energy from the sun and utilize it during the fertilization process.
2. Plants absorb solar energy from the sun and utilize it during the process of photosynthesis to turn it into plant matter.
3. Plants absorb solar energy from the sun and utilize it to increase the temperature inside them.
4. Plants absorb solar energy from the sun and utilize it during the shedding of their leaves and fruits.

If an engine were constructed to perform such that there would be no losses due to friction, what would be its efficiency?

1. It would be 0 percent.
2. It would be less than 100 percent.
3. It would be 100 percent.
4. It would be greater than 100 percent.

Entropy never decreases in a spontaneous process. Give an example to support this statement.

1. The transfer of energy by heat from colder bodies to hotter bodies is a spontaneous process in which the entropy of the system of bodies increases.
2. The melting of an ice cube placed in a room causes an increase in the entropy of the room.
3. The dissolution of salt in water is a spontaneous process in which the entropy of the system increases.
4. A plant uses energy from the sun and converts it into sugar molecules by the process of photosynthesis.

What is the advantage of a heat pump as opposed to burning fuel (as in a fireplace) for keeping warm?

1. A heat pump supplies energy by heat from the cold, outside air.
2. A heat pump supplies energy generated by the work done.
3. A heat pump supplies energy by heat from the cold, outside air and also from the energy generated by the work done.
4. A heat pump supplies energy not by heat from the cold, outside air, nor from the energy generated by the work done, but from more accessible sources.

What is thermal efficiency of an engine? Can it ever be 100 percent? Why or why not?

1. Thermal efficiency is the ratio of the output (work) to the input (heat). It is always 100 percent.
2. Thermal efficiency is the ratio of the output (heat) to the input (work). It is always 100 percent.
3. Thermal efficiency is the ratio of the output (heat) to the input (work). It is never 100 percent.
4. Thermal efficiency is the ratio of the output (work) to the input (heat). It is never 100 percent.

When would 100 percent thermal efficiency be possible?

1. When all energy is transferred by heat to the environment
2. When mass transferred to the environment is zero
3. When mass transferred to the environment is at a maximum
4. When no energy is transferred by heat to the environment