1. ELECTROMAGNETIC WAVES

2. Current can be induced in a coil by a changing magnetic field. A changing magnetic field induces a changing electric field at right angles to it. THE FACTS ABOUT ELECTROMAGNETIC RADIATION

3. A changing electric field induces a changing magnetic field at right angles to it. An accelerating charge has associated with it a changing magnetic field. Each field generates the other and can continue to do so in any medium that can contain electric and magnetic fields. Therefore electromagnetic waves can be set up by charges that oscillate backwards and forwards.

4. Propagation of an electromagnetic wave through space/air

5. Basic principle of an electromagnetic wave Assume represents the magnetic componentandrepresents the electric component generated at right angles to it Direction of propagation

6. James Clark Maxwell The genius of this man predicted mathematically the existence of electromagnetic waves. Nine years after the death of Maxwell, Heinrich Hertz produced and detected electromagnetic radio waves.

7. Maxwell predicts the speed of electromagnetic waves

8. The permittivity (ε) of a medium is a measure of its ability to hold an electric field. ε 0 = the permeability of empty space ε 0 = (4 π X 8,988 X 10 -7 ) -1 wave velocity = (ε 0 Xμ 0 ) -1/2 = 2,288 X 10 8 m.s -1 This is very close to the measured value of 3,13 X 10 8 m.s -1

9. Characteristics of electromagnetic waves They are produced by oscillating charges. An oscillating electric field is at right angles to an oscillating magnetic field. The two fields are in phase with each other. Electromagnetic waves are transverse waves.

10. Electromagnetic waves do not need a physical medium to travel in. All electromagnetic waves travel at a speed of 3 X 10 8 m/s (c). c = f. λ Electromagnetic waves have a particle nature as well and the energy of the photons E = h. f

11. Electromagnetic waves and energy c = f. λ and because c is a constant value, when f increases λ decreases. E = hf, where h is Planck’s constant. The higher the frequency of an electromagnetic wave, the higher the energy of the photons.

12. Proving that light (an electromagnetic wave) is also a transverse wave. Polaroid sheets have crystals of quinine iodosulphate deposited on them. These crystals are needle-like in shape and have their axes parallel to each other. The crystals transmit light vibrating in the same plane as the crystal axis and absorb light vibrating at right angles to this plane.

13. http://www.daviddarling.info/images/Polaroid_disks.jpg Polaroid lenses eliminating light