How to Draw Ray Diagrams for IGCSE Physics

Ray diagrams are tested directly in IGCSE Physics exams. Each mark is for a specific feature: the normal, angle labels, arrow directions, or correct bending.

Reflection ray diagram

1. Draw the mirror as a straight line.
2. Draw the normal as a dashed line perpendicular to the mirror at the point of incidence.
3. Draw the incident ray with an arrow pointing towards the mirror.
4. Draw the reflected ray with an arrow pointing away from the mirror.
5. Label the angle of incidence (i) between the incident ray and the normal.
6. Label the angle of reflection (r) between the reflected ray and the normal.
7. Mark that i = r.

Refraction ray diagram

1. Draw the boundary between the two media (e.g., air and glass).
2. Draw the normal as a dashed line perpendicular to the boundary at the point of incidence.
3. Draw the incident ray in the first medium.
4. Draw the refracted ray in the second medium. If entering a denser medium, the ray bends towards the normal. If entering a less dense medium, it bends away from the normal.
5. Label the angle of incidence and the angle of refraction.

Converging lens ray diagram

Use three standard rays from the top of the object:

1. A ray parallel to the principal axis: after the lens, it passes through the focal point (F) on the other side.
2. A ray through the centre of the lens: it passes straight through undeviated.
3. A ray through the focal point (F) on the same side as the object: after the lens, it emerges parallel to the principal axis.

The image forms where these rays meet (or appear to come from, for virtual images).

Tips

• Use a sharp pencil and a ruler for all straight lines.
• Draw arrows on every ray to show the direction of light travel.
• Label F (focal point) on both sides of the lens.
• For a virtual image, show the rays diverging after the lens and extend them backward with dashed lines to find the image position.