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Grade 8 · Science

Connect wave measurements

Use stated wave speed, frequency, wavelength and amplitude definitions to interpret simple measurements.

6 authored questions + worked example

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Worked example

Wave speed = frequency × wavelength. A wave has frequency 3 Hz and wavelength 2 m. What is its speed?

Answer & why

Answer: 6 m/s

3 cycles/s × 2 m/cycle = 6 m/s.

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All questions

All 6 authored questions for this skill.

Question 1

A wave travels at 20 m/s and has wavelength 5 m. What is its frequency?

  1. 25 Hz
  2. 4 Hz
  3. 15 Hz
  4. 100 Hz
A hint

Use speed = frequency × wavelength, and keep amplitude separate from frequency.

Answer & why

Answer: 4 Hz

20 ÷ 5 = 4 cycles per second.

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Question 2

Amplitude is maximum displacement from equilibrium. A point moves at most 2 cm from equilibrium. What is its amplitude?

  1. 2 Hz
  2. 0 cm
  3. 4 cm
  4. 2 cm
A hint

Use speed = frequency × wavelength, and keep amplitude separate from frequency.

Answer & why

Answer: 2 cm

The given maximum displacement is the amplitude, not a frequency.

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Question 3

Two waves in the same unchanged medium travel at the same speed. Wave B has twice A's frequency. How does B's wavelength compare?

  1. It is half as long.
  2. It is twice as long.
  3. It must be zero.
  4. It must be unchanged.
A hint

Use speed = frequency × wavelength, and keep amplitude separate from frequency.

Answer & why

Answer: It is half as long.

For a fixed speed, wavelength is speed divided by frequency.

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Question 4

A sensor records 15 complete cycles in 5 seconds. What is the measured frequency?

  1. 75 Hz
  2. 3 Hz
  3. 10 Hz
  4. 0.33 Hz
A hint

Use speed = frequency × wavelength, and keep amplitude separate from frequency.

Answer & why

Answer: 3 Hz

15 cycles ÷ 5 seconds = 3 cycles per second.

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Question 5

Wave speed = frequency × wavelength. A wave has frequency 3 Hz and wavelength 2 m. What is its speed?

  1. 5 m/s
  2. 1 m/s
  3. 6 m/s
  4. 1.5 m/s
A hint

Use speed = frequency × wavelength, and keep amplitude separate from frequency.

Answer & why

Answer: 6 m/s

3 cycles/s × 2 m/cycle = 6 m/s.

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Question 6

A wave travels at 12 m/s with frequency 4 Hz. Using speed = frequency × wavelength, what is its wavelength?

  1. 48 m
  2. 3 m
  3. 16 m
  4. 8 m
A hint

Use speed = frequency × wavelength, and keep amplitude separate from frequency.

Answer & why

Answer: 3 m

12 ÷ 4 = 3 meters per cycle.

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