Reflection & Absorption & Transmission

What is reflection?

When a wave changes direction at a boundary and travels back into its original medium.

What is the incident ray?

The ray travelling towards a surface.

What is the reflected ray?

The ray travelling away from a surface after reflection.

What is the normal?

An imaginary line drawn perpendicular to the surface at the point of incidence.

What is the angle of incidence?

The angle between the incident ray and the normal.

What is the angle of reflection?

The angle between the reflected ray and the normal.

State the law of reflection.

The angle of incidence equals the angle of reflection.

How should angles be measured in reflection diagrams?

From the normal, not from the surface.

What happens when a ray strikes a mirror along the normal?

It is reflected back along the same path.

How can a reflection ray diagram be constructed?

Draw the normal, incident ray and reflected ray, ensuring the angles of incidence and reflection are equal.

What is transmission?

When a wave passes through a material or boundary.

What is absorption?

When energy carried by a wave is transferred to the material.

What may happen when a wave reaches a boundary between materials?

It may be reflected, transmitted or absorbed.

Can reflection and transmission happen at the same boundary?

Yes, some energy may be reflected while the remainder is transmitted or absorbed.

What is specular reflection?

Reflection from a smooth surface, with parallel incident rays remaining parallel after reflection.

What is diffuse reflection?

Reflection from a rough surface, scattering light in different directions.

Why does a smooth mirror form a clear image?

It produces specular reflection, preserving the arrangement of reflected rays.

Why does a rough surface scatter light?

Its surface has different local orientations, so light reflects in different directions.

Does diffuse reflection disobey the law of reflection?

No, each individual ray still obeys the law of reflection.

Why does a black surface usually reflect less visible light than a white surface?

It absorbs more visible light and reflects less.