Wave Properties — Practice · Grade 8 Science

Chapter: Waves, Sound & Light

What this practice covers

By the end of Wave Properties you should be able to:

11 questions, numeric, multiple choice and written answer, each with a worked explanation.

Vocabulary used: wave, amplitude, wavelength (λ), frequency (f), period (T), model, evidence, system boundary, assumption.

Problem 1

A wave has a frequency of 3 Hz and a wavelength of 6 m. Find its speed.
Answer and explanation

18 m/s

v = f × λ = 3 × 6 = 18 m/s.

Problem 2

A wave has a period of 0.5 seconds. What is its frequency?
Answer and explanation

2 Hz

f = 1 ÷ T = 1 ÷ 0.5 = 2 Hz.

Problem 3

A wave travels at 12 m/s and has a frequency of 4 Hz. Find its wavelength.
Answer and explanation

3 m

λ = v ÷ f = 12 ÷ 4 = 3 m.

Problem 4

Which wave property is most directly related to the amount of energy a wave carries?
  1. wavelength
  2. amplitude
  3. period
  4. frequency only
Answer and explanation

amplitude

A bigger amplitude means more energy is being carried by the wave.

Problem 5

The distance from one wave crest to the next crest is the…
  1. amplitude
  2. period
  3. wavelength
  4. frequency
Answer and explanation

wavelength

Wavelength is the distance between two matching points, such as crest to crest.

Problem 6

A wave has a frequency of 50 Hz and travels at 200 m/s. Find its wavelength.
Answer and explanation

4 m

λ = v ÷ f = 200 ÷ 50 = 4 m.

Problem 7

A wave travels at 12 m/s with wavelength 3 m. Find frequency and period. Explain the reasoning in your own words.
Answer and explanation

4 Hz and 0.25 s per cycle.

Frequency=v/λ=12/3=4 Hz.

Period=1/f=1/4=0.25 s.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 8

A wave has frequency 5 Hz and wavelength 0.6 m. Find speed. Show the reasoning, not just the conclusion.
Hints

Hz means cycles per second, not meters per second.

Answer and explanation

v=5×0.6=3 m/s.

Problem 9

A floating marker bobs as waves pass. Must it travel across the pond with the wave?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. Waves transfer energy; local matter mainly oscillates in a simple wave model, though real water can also have currents.

Problem 10

A traveling wave and local material motion differA traveling wave and local material motion differt0t1t2Disturbance travels rightMarked rope location moves up/down locally; it does not ride the crest across.
The three conceptual rope snapshots show a pattern shifting along the rope while a marked location retains its horizontal coordinate and changes vertical position. The rope wave carries a disturbance and energy; a piece of rope does not need to move from source to receiver. These qualitative snapshots omit time scales and are not a calibrated wave-speed measurement.
For this unit’s illustrated case, what is wrong with tracing the red rope mark along the moving crest to the far right?
Answer and explanation

That would confuse the traveling pattern with the local motion of the material. The marked rope location oscillates locally rather than being carried across with the crest.

Follow one material marker rather than only a crest. A transverse rope wave has local motion perpendicular to travel. Sound uses a different local-motion direction, so do not assume every mechanical wave looks like a vertical rope curve.

That would confuse the traveling pattern with the local motion of the material. The marked rope location oscillates locally rather than being carried across with the crest.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 11

A supplied wave has wavelength 0.8 m and frequency 5 Hz. Find wave speed. If its matched-model amplitude doubles at the same medium/frequency/duration, what happens to the squared-amplitude energy comparison?
Answer and explanation

Speed 0.8×5 = 4 m/s. The represented energy increases by a factor of four under the stated matched squared-amplitude comparison.

Combine a spatial repeat and a temporal repeat.

Keep all named comparison conditions fixed before using the amplitude pattern.

Speed 0.8×5 = 4 m/s. The represented energy increases by a factor of four under the stated matched squared-amplitude comparison.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

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