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Science Physics — LET Practice Questions

This Science Physics section of the LET General Education exam covers 11 expert-reviewed practice questions. Each question has a plain-English explanation and notes on why the wrong answers are wrong.

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Sample questions with answers and explanations

Sample 1

A steel needle, carefully placed, can rest on the surface of water due to _________________.

Answer: A

Surface tension is a 'skin' on the water's surface caused by water molecules pulling on each other. A carefully placed steel needle rests on this skin even though steel is denser than water — the 'skin' holds it up.

Why the other choices are wrong
  • B. Atmospheric pressure pushes air down on everything equally — it doesn't specifically keep objects floating on water.
  • C. Buoyancy can't explain it — steel is denser than water, so without the surface 'skin' the needle would sink.
  • D. Viscosity is how thick/resistant a fluid is (honey vs. water) — water's low viscosity isn't what holds the needle.

Sample 2

What do you call sound with a frequency below 20 Hz?

Answer: C

Humans hear sounds from 20 Hz to 20,000 Hz. INFRAsonic = BELOW 20 Hz (too low to hear — elephants and whales use these). ULTRAsonic = ABOVE 20,000 Hz (too high to hear — bats and dogs use these). Memory trick: 'infra' = below (like infrared = below red light).

Tip: INFRA = below, ULTRA = above. SUB/SUPER = sonic speeds (slower/faster than sound).

Why the other choices are wrong
  • A. Supersonic = traveling FASTER than the speed of sound (a speed term, not frequency).
  • B. Subsonic = traveling SLOWER than the speed of sound (also a speed term).
  • D. Ultrasonic = sound ABOVE human hearing (above 20,000 Hz), opposite of what's asked.

Sample 3

What happens when vapor condenses into a liquid?

Answer: B

When water vapor turns back to liquid (condensation), it RELEASES heat. Think about it: to turn liquid water INTO vapor, you must add heat (boiling). Going BACKWARD, that heat must come back out. That's why steam burns are so bad — when steam condenses on your skin, it dumps that extra heat onto you.

Tip: Phase change rule: going to MORE ordered state (gas→liquid, liquid→solid) RELEASES heat. Going to LESS ordered (solid→liquid, liquid→gas) ABSORBS heat.

Why the other choices are wrong
  • A. Backwards. Condensation releases heat, not absorbs it. Evaporation absorbs.
  • C. Wrong direction, and temperature is not the point — during a phase change the temperature stays constant while heat leaves.
  • D. Temperature does not drop either — it holds steady at the condensation point. The real change is heat being released.
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