Unit 7: Modern Physics
Physics 2 · Unit 7 · Paper 2

Modern Physics unit test

A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.

Paper 1Paper 2Paper 3
Each paper is built from this unit’s 21 terms and is the same for everyone, so a teacher can assign “Unit 7, Paper 2” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.
Suggested time 37 min 34 points0/17 attempted
1

Wave-particle duality

2

Half-life

3

Emission vs absorption spectra

4

Photoelectric effect

5

de Broglie wavelength

6

Electron diffraction

7

Energy level diagrams

8

Alpha, beta and gamma decay

9

Photoelectric graph

10

Fission vs fusion

11

Conservation in nuclear reactions

12

Radioactive decay is random

Short answer 1. Define or explain: Work function

3 pts

Short answer 2. Define or explain: Stopping potential

3 pts

Short answer 3. Define or explain: Why intensity does not eject electrons below threshold

3 pts

Short answer 4. Define or explain: Nuclear notation

3 pts

Free response

10 pts

This course has no free-response prompt tagged to this unit, so one from elsewhere in the course is used. It is still worth writing — the skill transfers.

A heat engine operates between a hot reservoir at 500 K and a cold reservoir at 300 K. In each cycle it absorbs 600 J from the hot reservoir and exhausts 400 J to the cold reservoir.

Calculate the work output per cycle and the efficiency of the engine.

Calculate the maximum possible (Carnot) efficiency for these reservoirs and state whether the engine’s performance is physically allowed.

During one leg of the cycle the working gas absorbs 500 J of heat while doing 350 J of work on the piston. Calculate the change in internal energy and state what happens to the gas temperature.

Use the second law to explain why the exhaust heat cannot be reduced to zero.

Calculate the total entropy change of the two reservoirs per cycle and explain what its sign shows.