The law of reflection, why a change of speed bends a wave towards or away from the normal, and wavefronts.
What you will learn
- Use the law of reflection with angles measured from the normal
- Say which way a ray bends when it slows down or speeds up
- Explain refraction with wavefronts (Higher)
Reflection
When a wave hits a smooth surface it bounces off at the same angle it arrived at.
The normal is an imaginary line at 90° to the surface where the ray hits it. Every angle in a ray diagram is measured from the normal.
angle of incidence = angle of reflection
- A ray makes 25° with a mirror's surface
- angle of incidence = 90° − 25° = 65°
- angle of reflection = 65°
- angle between the two rays = 65° + 65° = 130°
At any boundary a wave can also be transmitted (it passes through) or absorbed (the material takes its energy). Most real boundaries do a mix of all three.
The rest of this lesson and its 10 practice questions are locked.
In this lesson
- Reflection
- Refraction: a change of speed
- Wavefronts (Higher)
- Try it: Bend a ray yourself
- Try it: Read a ray diagram
10 practice questions, marked as you go; about 25 minutes in all.
Key terms
Normal, Towards, Away from
In this unit: Waves and the electromagnetic spectrum
Transverse and longitudinal waves, v = fλ and the wave practicals, reflection and refraction, and the electromagnetic spectrum with its uses, dangers and the infrared practical.