1. Electromagnetic Radiation
Elliott

2. Spectrum
The EM spectrum is a family of waves that have the following properties:
They are Transverse
They travel at 3 x108 m/s
They can travel in a vacuum.

3. They are made up of an electric field and a magnetic field at 90o to each other.   The electric field (E) and the magnetic field (B) are always in phase (in step) with each other.

4. Main parts of the EM spectrum

5. Visible Light Light shows wave behaviour: It refracts, and reflects;
It is diffracted;
As a transverse wave, it can be polarised.

6. What evidence is there that light is a wave?
Check Your Progress
What evidence is there that light is a wave?  

7. Answer It can be polarised; It diffracts;
It is reflected and refracted.

8. Wave Equation
Speed of light
Wavelength
frequency

9. Check Your Progress

10. Answer

11. Photons
Physicists now believe that light travels in packets of waves called photons.
Each photon is a train or burst of waves. 
Photons are given out when charged particles lose energy. 
These travel in random directions from a light source. 
Once they have left the light source, the photons travel in straight lines until reflected or refracted.

12. The energy of each photon is given by the simple equation:
E = hf
E – energy per photon (J);
h – Planck’s constant, × 10-34 J s (joule-seconds, NOT joules per second)
 f – frequency  (Hz)
Photons are pure energy.  They have zero mass, which means that they can travel at the speed of light, 3.0 × 108 m s-1.

13. Evidence For Photons
Consider an old-fashioned black and white picture taken on a film.  We take the picture using a negative.  We then expose photographic paper to the negative using an enlarger.  We make a negative of a negative which makes a positive.  We then develop the image using chemicals.   A very short exposure shows random dots of silver.

15. Wavelengths are often given rather than frequency, so we have to convert to frequency using:

16. Power of a Beam of Light
If we have n photons, each of energy E, passing a particular point, we can easily work out the power P (energy per second).
P = nhf
If we know the power of a laser beam, we can work out many photons it gives out every second.

18. Check Your Progress

19. Answer