# 6.2.3 EM Waves & Matter

Higher Tier Only

### Interaction of Different Substances

• When EM waves move from one medium to another the waves might be:
• Transmitted
• Absorbed
• Reflected
• Refracted

When waves move from one medium to another they can be transmitted, reflected, refracted or absorbed

• The material interacts differently with different parts of EM spectrum because of the difference in wavelength
• Whilst some wavelengths might be transmitted, others might be reflected, refracted or absorbed
• Which of the interactions happen depends on:
• The wavelength of the waves
• The material the wave is travelling through
• For example, glass will:
• Transmit and/or refract visible light
Higher Tier Only

### Refraction of EM Waves

• Some effects, for example, refraction, are due to the difference in velocity of the waves in different substances
• Although all electromagnetic waves travel at the same speed in a vacuum, when they encounter certain materials (water, glass, oil) they will slow down
• How much they slow down depends on the material
• This slowing of electromagnetic waves causes them to refract
• A simple example of this is the refraction of visible light when it enters (or leaves) a glass block, although other electromagnetic waves can also refract

When electromagnetic waves pass through matter, their interactions slow them down causing them to refract

Higher Tier Only

### Wavefront Diagrams

• When a wave hits a different medium the different parts of the wave enter the medium at different times
• Hence, this leads to a change in speed
• The difference in speed between the parts of the wave in the first medium and the parts in the second medium causes the wave to bend
• Hence, this leads to a change in direction
• Refraction can be represented using wavefront diagrams, as shown below:

The different parts of the wave enter the second medium at different times causing the wave to bend

### Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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