Year 9 Science · Unit 4 · Lesson 3

Wave Properties — Amplitude, Wavelength, Frequency

Challenge Worksheet

Name

Date

Class

Learning Goals

Apply the wave speed equation (v = fλ) to calculate frequency from a wave diagram.
Analyse the tsunami amplitude–energy relationship to explain destructive power near shore.
Construct extended scientific arguments about energy, amplitude, and wavelength interactions.

Warm Up

Order the steps

Number the steps from 1 to 7 to show the correct procedure for calculating frequency from a wave diagram. Step 1 = what you do first.

Order	Step
	Substitute the known wave speed and your calculated wavelength into the formula f = v ÷ λ.
	Count the number of complete wavelengths visible in the diagram.
	Check that your answer has units of hertz (Hz) — if not, recheck your working.
	Divide the total length of the diagram (in metres) by the number of complete wavelengths to find one wavelength (λ).
	Calculate the frequency and record the result.
	Identify the total length of the diagram shown (in metres) from the scale or axis labels.
	Rearrange the wave equation v = fλ to make frequency the subject: f = v ÷ λ.

Go Deeper

Evaluate the claim

Real-world context

The 2004 Indian Ocean tsunami, which caused catastrophic damage to coastal regions of Indonesia, Sri Lanka, and Australia's Cocos (Keeling) Islands territory, was generated by a magnitude 9.1 earthquake. In deep ocean water, the tsunami had a wavelength of approximately 200 km and an amplitude of only about 0.5–1 m — ships at sea barely noticed it passing. Yet as the wave approached the shallow coast near Banda Aceh, Indonesia, its wavelength compressed to a few kilometres and its amplitude surged to over 30 m, releasing enormous destructive energy on the shore. Geoscience Australia used deep-ocean pressure sensors (DART buoys) to detect and monitor the wave.

(a) Using the relationship energy ∝ amplitude², explain why the tsunami near shore at Banda Aceh was so much more destructive than the same wave in deep ocean. Include a numerical comparison in your answer.

Challenge 3 marks

(b) Ships in deep ocean did not notice the tsunami, even though it was passing beneath them. Explain why the very small amplitude in deep water means the wave is nearly undetectable, despite carrying enormous total energy across its 200 km wavelength.

Challenge 3 marks

(c) As the tsunami moved into shallow water, its wavelength compressed from ~200 km to a few kilometres. Using your knowledge of wave properties, explain what must happen to the amplitude when wavelength decreases, and why this relationship means coastal communities face the greatest danger.

Challenge 4 marks

Wrap Up

In one sentence, what was the main idea of this lesson?