38. Refraction of Waves

GCSE Physics: Refraction of Waves

Refraction is the change in direction of a wave as it passes from one medium to another (e.g., from air into glass).

Waves travel at different speeds in different materials due to their density.
For electromagnetic waves like light: Higher density = Slower speed.
Air to Glass: The light slows down as it enters the more dense glass.
Glass to Air: The light speeds up as it enters the less dense air.

Perpendicular Entry: If a wave hits the boundary at 90 degrees (along the normal), it does not change direction; it continues straight through.
Angled Entry:
- Entering a more dense medium: The wave slows down and bends towards the normal.
- Entering a less dense medium: The wave speeds up and bends away from the normal.

To draw a complete ray diagram for light passing through a glass block:

Incident Ray: Draw the incoming light ray hitting the boundary at the point of incidence.
First Normal: Draw a dashed line perpendicular to the surface at that point.
Refracted Ray: Draw the ray inside the glass bending towards the normal.
Second Normal: Draw another dashed line where the ray hits the exit boundary.
Emergent Ray: Draw the ray leaving the glass bending away from the normal.
Labeling: Include the angle of incidence and the angle of refraction.

Using the wave speed equation (v = f x $\lambda$ ):

Frequency (f): Remains constant during refraction.
Wavelength ( $\lambda$ ): Changes in proportion to the speed.
- If speed decreases (e.g., entering glass), the wavelength decreases.
- If speed increases (e.g., entering air), the wavelength increases.

Different wavelengths (colors) of light are refracted by different amounts.
White Light: Contains all colors of the visible spectrum.
The Effect: When white light passes through a triangular prism, each color bends at a slightly different angle, causing the light to spread out into a rainbow.