GCSE Physics revision

Properties of electromagnetic waves 1

Electromagnetic waves

AQA 4.6.2.2

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AQA student objectives

Learning pathway

ALL 🎯

Construct ray diagrams to illustrate the refraction of a wave at the boundary between two different media.

MOST 🎯🎯

Apply the specified scientific knowledge of properties of electromagnetic waves 1 to a relevant example.

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Analyse an unfamiliar example of properties of electromagnetic waves 1 using the specified scientific ideas.

Revision summary

Read on screen, then print for Cornell-style active revision.

Different objects and substances can interact with electromagnetic waves in different ways, and this interaction can depend on the wavelength of the wave.
A red t-shirt reflects light with a wavelength of approximately 650 nm (red light) and absorbs all other wavelengths, which is why it appears red.
Whether a wave is absorbed or reflected by a material can vary with wavelength — this wavelength dependence is a higher tier concept at GCSE.
What is Refraction?
Refraction occurs when a wave speeds up or slows down as it moves from one medium to another, causing it to change direction.
When light travels from air into a glass block, it slows down and bends towards the normal (an imaginary line perpendicular to the surface).
When light exits the glass block back into air, it speeds up again and bends away from the normal.
The change in direction is always caused by a change in speed — this is the key principle of refraction.

1. How Objects Interact with WavesAQA

Different objects and substances can interact with electromagnetic waves in different ways, and this interaction can depend on the wavelength of the wave.
A red t-shirt reflects light with a wavelength of approximately 650 nm (red light) and absorbs all other wavelengths, which is why it appears red.
Whether a wave is absorbed or reflected by a material can vary with wavelength — this wavelength dependence is a higher tier concept at GCSE.
What is Refraction?
Refraction occurs when a wave speeds up or slows down as it moves from one medium to another, causing it to change direction.
When light travels from air into a glass block, it slows down and bends towards the normal (an imaginary line perpendicular to the surface).
When light exits the glass block back into air, it speeds up again and bends away from the normal.
The change in direction is always caused by a change in speed — this is the key principle of refraction.

A ray diagram of refraction shows the incident ray, the normal at the boundary, and how the ray changes direction as it enters and exits a denser medium such as glass.
The incident ray is the incoming ray of light before it reaches the boundary between two media.
Drawing the normal at each boundary helps show clearly whether the refracted ray bends towards or away from the normal.

2. Ray Diagrams of RefractionAQA

A ray diagram of refraction shows the incident ray, the normal at the boundary, and how the ray changes direction as it enters and exits a denser medium such as glass.
The incident ray is the incoming ray of light before it reaches the boundary between two media.
Drawing the normal at each boundary helps show clearly whether the refracted ray bends towards or away from the normal.

Refraction can also be illustrated using wavefronts, which show how the direction of a wave changes at a boundary between two media.
In shallow water, waves travel faster, whilst in deep water they slow down, causing the wavefronts to change direction towards the normal.
The part of the wavefront that reaches the boundary first changes direction first, which causes the entire wavefront to bend.
When a wave slows down, its wavelength becomes shorter, so wavefronts appear closer together in the slower medium.

3. Refraction Using WavefrontsAQA

Refraction can also be illustrated using wavefronts, which show how the direction of a wave changes at a boundary between two media.
In shallow water, waves travel faster, whilst in deep water they slow down, causing the wavefronts to change direction towards the normal.
The part of the wavefront that reaches the boundary first changes direction first, which causes the entire wavefront to bend.
When a wave slows down, its wavelength becomes shorter, so wavefronts appear closer together in the slower medium.

The fundamental cause of refraction is always a change in the speed of the wave — no change in speed means no change in direction.
When a wave slows down upon entering a new medium, it bends towards the normal and its wavelength decreases.
When a wave speeds up upon entering a new medium, it bends away from the normal and its wavelength increases.

4. Key Principles to RememberAQA

The fundamental cause of refraction is always a change in the speed of the wave — no change in speed means no change in direction.
When a wave slows down upon entering a new medium, it bends towards the normal and its wavelength decreases.
When a wave speeds up upon entering a new medium, it bends away from the normal and its wavelength increases.