The law of reflection, smooth and rough surfaces, and the required practical that traces rays through a glass block.
What you will learn
- Measure angles of incidence, reflection and refraction from the normal
- Tell specular reflection from diffuse reflection
- Plan the glass block practical and analyse its results
Angles are measured from the normal
The normal is an imaginary line at 90° to a surface, drawn where the ray hits it.
Every angle in a ray diagram is measured from the normal, never from the surface.
At a mirror, the angle of reflection equals the angle of incidence.
- A ray makes 25° with the surface of a mirror
- angle of incidence = 90° − 25° = 65°
- angle of reflection = 65°
- the incident and reflected rays are 65° + 65° = 130° apart
The classic slip: using the angle to the mirror surface. Draw the normal first, then measure.
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- Angles are measured from the normal
- Smooth or rough
- The glass block practical
- Try it: Try it in the refraction sim
- Try it: Angles at a mirror
8 practice questions, marked as you go; about 25 minutes in all.
Key terms
Normal
In this unit: Lenses, visible light, sound and black bodies
Reflection and the glass block practical, total internal reflection and optical fibres, colour and filters, lenses and magnification, sound and echoes, ultrasound and seismic waves, and black body radiation (Physics only).