Explain it

06.10 — 4 short write-ups

Question 1 of 4

A checkpoint, not a test

DBA rehearsal: photoelectric effect

Answer as if the instructor asked this aloud.

In the photoelectric effect, why can brighter light below threshold still fail to eject electrons, while higher-frequency light above threshold can increase their maximum kinetic energy?

Compare photon count with energy per photon.

Question 2 of 4

A checkpoint, not a test

DBA rehearsal: melting and energy

Rehearse aloud, then write a few sentences in your own words.

A heater keeps adding energy while a substance melts at constant temperature. Explain where that energy goes and which heat equation applies.

Connect the flat part of the heating curve to what the particles are doing.

Question 3 of 4

A checkpoint, not a test

DBA rehearsal: nuclear changes

Rehearse aloud, then write a few sentences in your own words.

Compare fission and fusion. Then explain how gamma emission changes a nucleus without changing its element.

Separate combining or splitting nuclei from a change in nuclear energy.

Question 4 of 4

A checkpoint, not a test

DBA rehearsal: clocks and lengths

Rehearse aloud, then write a few sentences in your own words.

An observer measures a clock and a meterstick moving together at a speed close to the speed of light. Compared with their rest-frame measurements, how do the clock’s ticking rate and the meterstick’s length along the motion change? What happens to a length perpendicular to the motion?

Name the frame, then distinguish ticking rate from the interval between ticks.