Presentation on theme: "Option G – Electromagnetic waves. Lesson 1 Outline the nature of electromagnetic (EM) waves. Describe the different regions of the electromagnetic spectrum."— Presentation transcript:
Option G – Electromagnetic waves
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.
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.
Electromagnetic spectrum λ nm λ m λ m λ m λ m λ m λ m
Source of electromagnetic waves? You have 15 minutes to take notes from pages 600 and 601 about how different EM waves are produced.
TypeSource Radio Microwaves Infra-red Visible Ultraviolet X Ray Gamma Sources of EM radiation TypeSource Radio Vibrating electrons e.g. AC current Microwaves Excited semiconductors or vibrating electrons Infra-red Electrons transitions between energy levels Visible Electrons transitions between energy levels Ultraviolet Electrons transitions between energy levels X Ray Emitted when decelerate rapidly electrons e.g. when they hit a metal target Gamma Emitted by nuclei after a nuclear reaction
Dispersion Lets make rainbows!
A reminder - Snells law speed in substance 1 sinθ 1 speed in substance 2 sinθ 2 =
A reminder - Snells law In the case of light only, we usually define a quantity called the index of refraction for a given medium as n = c c m where c is the speed of light in a vacuum and c m is the speed of light in the medium vacuum c cmcm
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.