2.1 Introduction
2.2 Generation of Electromagnetic Waves
2.2.1 Speed of Electromagnetic Waves
2.2.2 Direction of Propagation of Electromagnetic Waves
2.2.3 Doppler Effect of Electromagnetic Waves
2.3 The Electromagnetic Spectrum
2.4.1 Energy Carried by Electromagnetic Waves
2.4.2 Radiation Pressure
2. Summary
Unit 2 - Multiple Choice - Electromagnetic Waves Questions
Unit 2 - Multiple Choice - Electromagnetic Waves Answers
Unit 2.1 Multiple Choice Extended Questions - Waves
Unit 2.1 Multiple Choice Extended Answers-Waves
 

Unit 2 Electromagnetic Waves

2.1 Existence of Electromagnetic Waves

2.1.1 Symmetry Arguments

So far we have looked at mechanical waves.

We will now examine the properties of electromagnetic waves, which unlike mechanical waves can propagate through empty space.

Electromagnetic Waves

— are waves composed of vibrating electrical and magnetic fields.

— such as light and radio waves, form the electromagnetic spectrum.

— have the same speed in a vacuum, expressed by the letter c (the speed of light) and equal to about 3.0 X 108ms-1.

— transport energy, due to oscillating electric and magnetic fields.

— are called electromagnetic radiation, light, or photons.

Question: The strength of the attraction between two charges depends on the square of the distance between them. How does each charge know the distance and magnitude of the other charge?

When one charge moves it creates a disturbance in the field which launches an electromagnetic wave. The wave propagates away from the disturbance and informs the whole universe of the disturbance..

Maxwell's equations predicted the existence of electromagnetic waves (EM) that propagate through space at the speed of light (c) according to the traveling wave analysis model.

Maxwell's Laws

maxwells equations

In words:

1. Relationship between electric field and its source.

2. Relationship between magnetic field and its source, however magnetic filed lines are continuous whereas electric filed lines begin and end on electric charges.

3. Relationship between electric field and a changing magnetic field.

4. Relationship between electric field and an electric current or changing electric filed.

Symmetry Argument

Recognizing many examples of symmetry in nature, Maxwell hypothesized that if a changing magnetic field produces an electric field, as given by Faraday’s law, then the reverse might be true as well: a changing electric field will produce a magnetic field.

Maxwell’s theory is a mathematical formulation that relates electric and magnetic phenomena. He predicted (in 1864) that

— a changing electric field produces a magnetic field.

— accelerating charges will radiate electromagnetic waves.

— electromagnetic waves travel at the speed of light (c) 3.0 X 108ms-1

— the electric and magnetic fields in the wave are fluctuating.

Maxwell’s idea was that a magnetic field can be caused not only by a normal electric current, but also by a changing electric field or changing electric flux.

In 1887, practical confirmation of this theoretical prediction was demonstrated by Heinrich Hertz when he actually generated and detected EM waves .

hertz

 

 

 

     
Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.