Option G – Electromagnetic waves
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Transcript of Option G – Electromagnetic waves
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
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 ≈ 700 - 420 nm
λ ≈ 10-7 - 10-8 m
λ ≈ 10-9 - 10-11 m
λ ≈ 10-12 - 10-14 m
λ ≈ 10-4 - 10-6 m
λ ≈ 10-2 - 10-3 m
λ ≈ 10-1 - 103 m
Source of electromagnetic waves?
• You have 15 minutes to take notes from pages 600 and 601 about how different EM waves are produced. http://phet.colorado.edu/sims/radio-waves/radio-waves_en.jar
Type Source
Radio
Microwaves
Infra-red
Visible
Ultraviolet
X Ray
Gamma
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 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
Let’s make rainbows!
A reminder - Snell’s law
speed in substance 1 sinθ1
speed in substance 2 sinθ2=
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 = ccm
where c is the speed of light in a vacuum and cm is the speed of light in the medium
vacuum
c
cm
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.
Dispersion
Just one question!Page 605 Question 3