Year 9 Science · Unit 4 · Lesson 1

What Are Waves?

Challenge Worksheet

Name
Date
Class

Learning Goals

Warm Up

Because… chain

An explosion occurs on the Moon's surface. Fill in the missing effects — each cause leads to the next step in the chain.

The Moon has no atmosphere — it is a vacuum.
→
Sound is a mechanical wave.
→
No medium exists for sound to travel through.
→
The explosion also releases light (an electromagnetic wave).
→
Electromagnetic waves do not need a medium.
→

Overall outcome — what an observer on Earth would experience:

Go Deeper

What if…?

Scenario

Imagine that the speed of light suddenly dropped to the same speed as sound in air — approximately 340 m/s. Currently, light from the Sun takes about 8 minutes to reach Earth, travelling at 300,000 km/s. Radio signals from satellites circle the globe in fractions of a second. At 340 m/s, light would now take over 400 years to travel from the Sun to Earth.

(a) How would this change affect what we see when we look at the Sun, stars, and distant galaxies? Use the idea of electromagnetic waves in your answer.

Challenge 3 marks

(b) GPS satellites orbit Earth at about 20,000 km altitude. Currently, signals reach your phone in milliseconds. Describe how satellite communication would change at the new speed of light, and explain the impact on everyday technology.

Challenge 3 marks

(c) Sound is a mechanical wave and is NOT affected by this scenario. Explain clearly why the change in light's speed has no effect on sound, and what this reveals about the difference between mechanical and electromagnetic waves.

Challenge 4 marks

Wrap Up

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

HSCScience · Year 9 Science · Unit 4 · Lesson 1 · Challenge Worksheet