A2L Item 193

Goal: Problem solving in thermodynamics

Source: UMPERG-ctqpe198

An
amount of an ideal gas is taken around the process shown.The amount of
heat extracted during process BC is

1. 10 J
2. 20 J
3. 15 J
4. 45 J
5. 60 J
6. none of the above
7. cannot be determined

Commentary:

(4) Since no work is done the change in internal energy must be
due to heat extraction. Some students may think that the answer cannot
be determined because they do not know the number of moles. These are
likely thinking that they need to find the temperature at each state to

A2L Item 110

Goal: Hone the concept of heat capacity

Source: UMPERG-ctqpe210

Two thermodynamic systems are made from the same material. The specific
heat of this material is independent of temperature. The bodies have
different masses and, initially, different temperatures as shown. If the
bodies are placed in thermal contact the final equilibrium temperature
is most nearly

1. 27 C
2. 33 C
3. 40 C
4. 47 C
5. None of the above
6. Cannot be determined

Commentary:

(4) It is valuable to ask students how they obtained their answer. Each
of the offered answers is obtained by a common conceptual or algebraic
mistake.

A2L Item 109

Goal: Problem solving with thermal energy.

Source: UMPERG-ctqpe208

A cup of water is about 225 grams. The minimum amount of heat needed to
boil a cup of water at room temperature for tea is most nearly

1. 10,000 cal
2. 17,000 cal
3. 25,000 cal
4. 31,000 cal
5. None of the above
6. Cannot be determined

Commentary:

(2) This problem requires that students know the specific heat of water
and assume that the water is initially at room temperature.

A2L Item 092

Goal: Hone the concept of heat and distinguish from internal energy.

Source: UMPERG-ctqpe191

Which of the following phrases best describes heat?

1. The total energy possessed by a body.
2. The flow of temperature to or from a body.
3. The amount of energy dissipated by friction.
4. The total energy flowing between two bodies at different temperatures.
5. The useful work that could be extracted from a body.