Year 9 Science · Unit 4 · Lesson 10

Checkpoint 2 — Sound, EM Spectrum, Light

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Learning Goals

Apply understanding of sound, EM waves, and light to identify what does not belong in a category.
Synthesise concepts from Lessons 6–9 to explain a real-world observation.
Distinguish between mechanical waves and electromagnetic waves in context.

Warm Up

Odd one out

Circle the item that does not belong in each group. Then explain why it doesn't fit in the answer column.

#	Group	Your answer (odd one + reason)
1	Radio waves Microwave Infrared Ultrasound
2	Cochlea Pinna Eardrum Lens
3	Reflection Refraction Absorption Diffraction
4	Gamma rays X-rays UV Infrasound

Your Turn

Scenario

During a solar eclipse visible from central Australia, the Moon passes directly in front of the Sun. A scientist at a remote outpost simultaneously: sees the sky darken almost instantly as the eclipse begins; hears no unusual sound from the sky; uses a handheld UV meter and notices radiation levels drop sharply; and feels the air temperature begin to fall within minutes.

(a) Why does the scientist see the eclipse happen immediately, but hear no sound from the Sun at all — not even during the eclipse?

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(b) Why does the UV meter reading drop during the eclipse? Which part of the EM spectrum is being blocked, and what is the source?

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(c) Why does the air temperature drop during the eclipse? Which part of the EM spectrum is responsible for heating the air, and what happens when it is blocked?

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(d) What does this eclipse event demonstrate about the difference between electromagnetic waves and mechanical (sound) waves?

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Wrap Up

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