Year 9 Science · Unit 4 · Lesson 9

Light Interactions

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Learning Goals

Warm Up

Because… chain

Fill in the missing effects. Each cause leads to the next step in the journey of a light ray through a glass window pane (air → glass → air).

Light travels in air and hits the glass surface at an angle
→
Glass is a denser medium than air
→
Light slows down inside the glass
→
Light exits the glass back into air
→
Light speeds up again as it re-enters air
→

Overall outcome (what happens to the light ray after passing through the glass?)

Your Turn

Real-world context

Australia’s NBN (National Broadband Network) uses optical fibre cables to carry internet data as pulses of light from exchanges to homes and businesses across the country. The fibre optic cables consist of a glass or plastic core surrounded by a cladding material with a lower refractive index. Light pulses bounce along the core for thousands of kilometres without escaping.

(a) Explain what total internal reflection is and describe the conditions needed for it to occur. Why does the glass core’s higher refractive index (compared to the cladding) keep the light trapped inside?

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(b) Why is glass (or plastic) used as the core of optical fibres rather than air? Refer to the conditions needed for total internal reflection in your answer.

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(c) Explain why optical fibre transmits data faster than a copper wire. Your answer should refer to the speed of light compared to the speed of electrical signals, and the bandwidth of the two systems.

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Wrap Up

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

HSCScience · Year 9 Science · Unit 4 · Lesson 9 · Apply Worksheet