Reflection & Refraction

Reflection definition

When a wave bounces off a surface

Law of reflection

Angle of incidence = angle of reflection

Incident ray

Incoming ray hitting a surface

Reflected ray

Ray that bounces off the surface

Normal line

Imaginary line at 90° to the surface

Angle of incidence

Angle between incident ray and normal

Angle of reflection

Angle between reflected ray and normal

Smooth surface reflection

Produces clear reflection (specular)

Rough surface reflection

Scattered reflection (diffuse)

Refraction definition

Change in direction of a wave when it enters a new medium

Cause of refraction

Change in wave speed

Light entering denser medium

Slows down and bends towards the normal

Light entering less dense medium

Speeds up and bends away from the normal

Wavelength change

Wavelength changes during refraction; frequency stays constant

Frequency in refraction

Remains the same

Speed change

Wave speed changes when medium changes

Ray diagram rule

Draw normal at boundary; show bending depending on density

Air to glass

Light bends towards normal

Glass to air

Light bends away from normal

Total internal reflection condition

Occurs when angle > critical angle in dense → less dense

Key idea

Reflection = bouncing; refraction = bending due to speed change

law of reflection diagram

law of refraction diagram