Year 7 Science · Unit 3 · Lesson 15

Light Energy — Reflection and Refraction

Apply Worksheet

Name

Date

Class

Learning Goals

Predict and explain apparent depth using refraction of light at a water surface.
Describe how optical fibres use repeated reflection to carry data.
Order the steps in a technology that relies on a specific light behaviour.

Warm Up

Scenario

An Australian spearfisher is standing on the edge of a rock platform at Jervis Bay, looking at a fish near the bottom of a 2.0 m deep pool. Because of the way light travels from water into air, the fish appears to be only about 1.5 m below the surface — shallower than it actually is. The spearfisher must aim at a slightly different spot to actually hit the fish.

(a) Predict: Should the spearfisher aim above or below where the fish appears to be? Write your prediction clearly before you explain.

Apply 1 mark

(b) Justify your prediction. Use these ideas in your answer: refraction, angle, bends away from normal, denser to less dense medium, apparent depth.

Apply 3 marks

Your Turn

Order the steps

Number the events from 1 to 7 to show the correct order of how an optical fibre carries internet data across Australia. Event 1 = what happens first.

Order	Event
	Light pulses travel along the glass fibre, bouncing off the inner walls by total internal reflection — they cannot escape sideways
	A detector at the receiving end converts the pattern of light pulses back into an electrical signal
	The electrical signal from your computer is converted into pulses of laser light at one end of the fibre
	The electrical signal is decoded and your webpage or video loads on screen
	Your computer sends a request (electrical signal) when you click a link or load a webpage
	The light pulses exit the end of the fibre after travelling hundreds of kilometres (e.g. Sydney to Melbourne via the National Broadband Network)
	The laser light enters the glass fibre, hitting the boundary at a very shallow angle so it cannot escape (total internal reflection)

Show What You Know

1. A camera lens focuses light from the outside world onto a sensor. Describe, in terms of refraction, what happens to the light rays as they pass through the curved glass lens. Use the words denser medium, bends toward normal, and converge.

Apply 3 marks

2. A student says "the angle of incidence is measured from the mirror surface." Explain the mistake and state the correct way to measure this angle.

Apply 2 marks

Wrap Up

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