Edexcel iGCSE Physics -3.9 Reflection and Refraction of Waves- Study Notes- New Syllabus

Reflection and Refraction of Waves

All waves including sound waves, water waves, and electromagnetic waves—can undergo reflection and refraction when they meet a boundary between different media.

These behaviours occur because waves change direction when they interact with surfaces or when their speed changes.

Reflection of Waves

Reflection occurs when a wave bounces off a surface and changes direction while remaining in the same medium.

• The wave does not pass into a new medium.
• The speed and frequency remain the same.
• The direction of travel changes.

Law of Reflection (applies to all waves):

\( \mathrm{angle\ of\ incidence = angle\ of\ reflection} \)

This law applies to sound, water waves, and light waves.

Refraction of Waves

Refraction occurs when a wave enters a different medium and its speed changes, causing the wave to change direction.

• The wave crosses a boundary.
• Wave speed changes.
• Wavelength changes.
• Frequency remains constant.

Why Refraction Occurs

• Different media affect wave speed differently.
• A change in speed causes bending of the wave.
• This bending is refraction.

Wave Relationship Used

The relationship between wave speed, frequency and wavelength is:

\( \mathrm{v = f\lambda} \)

• When a wave slows down, wavelength decreases.
• When a wave speeds up, wavelength increases.
• Frequency stays the same across boundaries.

Reflection and Refraction in Different Waves

• Water waves: reflect from barriers and refract in shallow water.
• Sound waves: reflect to form echoes and refract due to temperature changes.
• Light waves: reflect from mirrors and refract in glass or water.

Key Idea

• All waves can be reflected.
• All waves can be refracted.
• Refraction only occurs when wave speed changes.

Important Points to Remember

• Reflection does not change speed or frequency.
• Refraction changes speed and wavelength.
• Frequency never changes during refraction.