Refraction of light Flashcards – Cambridge IGCSE (9–1) Physics 0972 (Extended) (2026–2028)

What is refraction of light?

A change in light’s direction as it crosses a boundary between transparent media because its speed changes.

How does a light ray bend when it enters a medium where it travels more slowly or more quickly?

More slowly: towards the normal. More quickly: away from the normal.

What happens to a light ray incident along the normal as it crosses a boundary?

Its speed changes, but its direction does not.

What is the normal to a boundary where a light ray meets it?

An imaginary line perpendicular to the boundary at the point where the ray meets it.

How are the angles of incidence and refraction measured?

The angle of incidence is between the incident ray and the normal; the angle of refraction is between the refracted ray and the normal.

What path does light follow through a uniform transparent medium?

It travels in a straight line.

How can you trace a ray’s path through a transparent block on paper?

1. Place the block on paper, draw around it and direct a narrow ray at its surface.
2. Mark the incident and emerging rays and the entry and exit points.
3. Remove the block and join the entry and exit points.

How are the relevant angles measured on a ray trace through a transparent block?

Draw a normal at each boundary and use a protractor to measure the angles from the normals.

What does a ray trace show about the direction of light at the boundaries and within a uniform transparent block?

The light changes direction at the boundaries and travels in a straight line within the block.

What can be investigated by tracing rays through differently shaped blocks with different incident directions?

How the orientations of the boundaries affect the ray’s passage through the material.

What can happen when light reaches a boundary from a slower medium towards a faster medium?

Some light can be reflected internally while the rest is refracted across the boundary.

As the angle of incidence increases at a boundary from a slower to a faster medium, how does the angle of refraction change?

It increases.

What is the critical angle for light travelling from a slower to a faster medium?

The angle of incidence in the slower medium at which the refracted ray travels along the boundary, at $90^\circ$ to the normal.

What two conditions are required for total internal reflection?

Light must travel from a slower medium towards a faster medium, with an angle of incidence greater than the critical angle.

What happens to light at a boundary during total internal reflection?

All the light is reflected back into the first medium; no refracted ray crosses the boundary.

How does the angle of reflection compare with the angle of incidence during total internal reflection?

They are equal.

How should a narrow ray enter a semicircular block to investigate reflection at its flat face?

Direct it through the curved surface towards the centre of the flat face, so it meets the curved surface normally.

In a semicircular-block investigation of total internal reflection, what is varied and what rays are observed?

Vary the angle of incidence at the flat face and observe the refracted and internally reflected rays.

What are two uses of total internal reflection?

Guiding light along optical fibres and redirecting light in prisms in binoculars.