Year 8 · Science · Light and sound · Lesson 3

Light and reflection

How light travels, luminous and non-luminous objects, transparent, translucent and opaque materials, the law of reflection and ray diagrams, and mirror images.

25-minute video lesson

Teaching, worked examples and 20 practice questions solved step by step.

Watch free for a month

What your child will learn

Describe how light travels
Explain how we see objects
Classify materials as transparent, translucent or opaque
Use the law of reflection
Describe the image in a plane mirror

The method

Light travels in straight lines at 300 000 km/s and can travel through a vacuum.
We see non-luminous objects because light reflects off them into our eyes.
Law of reflection: angle of incidence = angle of reflection, measured from the normal.
A plane mirror image is the same size, upright, the same distance behind, and laterally inverted.

Key words: luminous, transparent, translucent, opaque, reflection, normal, angle of incidence, angle of reflection, plane mirror.

Worked examples

The first three practice questions from the lesson, with every step.

Question 1

The angle of incidence on a mirror is 40°. What is the angle of reflection?

Step 1: Look at the diagram
Step 2: Law of reflection: i = r
Step 3: r = 40°

Answer: 40°

Question 2

The angle of incidence on a mirror is 25°. What is the angle of reflection?

Step 1: Look at the diagram
Step 2: Law of reflection: i = r
Step 3: r = 25°

Answer: 25°

Question 3

The angle of incidence on a mirror is 60°. What is the angle of reflection?

Step 1: Look at the diagram
Step 2: Law of reflection: i = r
Step 3: r = 60°

Answer: 60°