1. Option G – Electromagnetic waves

2. Lesson 1 Outline the nature of electromagnetic (EM) waves.
Describe the different regions of the electromagnetic spectrum.
Describe what is meant by the dispersion of EM waves.
Describe the dispersion of EM waves in terms of the dependence of refractive index on wavelength.

3. Nature of electromagnetic waves

4. Nature of electromagnetic waves
An oscillating electric charge produces varying electric and magnetic fields.
Electromagnetic waves are transverse waves and all have the same speed in a vacuum.

5. Electromagnetic spectrum
λ ≈ nm
λ ≈ m
λ ≈ m
λ ≈ m
λ ≈ m
λ ≈ m
λ ≈ m

6. Source of electromagnetic waves?
You have 15 minutes to take notes from pages 600 and 601 about how different EM waves are produced.

7. Sources of EM radiation
Type
Source
Radio
Vibrating electrons e.g. AC current
Microwaves
Excited semiconductors or vibrating electrons
Infra-red
Electrons transitions between energy levels
Visible
Ultraviolet
X Ray
Emitted when decelerate rapidly electrons e.g. when they hit a metal target
Gamma
Emitted by nuclei after a nuclear reaction
Type
Source
Radio
Microwaves
Infra-red
Visible
Ultraviolet
X Ray
Gamma

8. Dispersion
Let’s make rainbows!

9. A reminder - Snell’s law
speed in substance 1 sinθ1
speed in substance 2 sinθ2 =

10. A reminder - Snell’s law
In the case of light only, we usually define a quantity called the index of refraction for a given medium as
n = c cm
where c is the speed of
light in a vacuum and cm
is the speed of light in the
medium c
vacuum cm

11. Dispersion
This occurs because the index of refraction of the glass changes with wavelength. The index of refraction is slightly smaller for red light than it is for blue light, so the red light gets bent less.

12. Dispersion

13. Just one question!
Page 605 Question 3