1. The electro-magnetic spectrum

3. Key facts
All the waves travel at the same speed – around km/s

4. Key facts All the waves are transverse waves
All the waves travel at the same speed – around km/s
All the waves are transverse waves

5. Key facts All the waves can be reflected and refracted
All the waves travel at the same speed – around km/s
All the waves are transverse waves
All the waves can be reflected and refracted

6. Key facts The longest waves are the radio waves
All the waves are transverse waves
All the waves can be reflected and refracted
The longest waves are the radio waves

7. Key facts The shortest waves are the gamma waves
All the waves can be reflected and refracted
The longest waves are the radio waves
The shortest waves are the gamma waves

8. Key facts The shorter the wavelength, the higher the frequency
The longest waves are the radio waves
The shortest waves are the gamma waves
The shorter the wavelength, the higher the frequency

9. Key facts All the waves travel at the same speed – around 300 000 km/s
All the waves are transverse waves
All the waves can be reflected and refracted
The longest waves are the radio waves
The shortest waves are the gamma waves
The shorter the wavelength, the higher the frequency

10. Key facts
The shorter the wavelength the more dangerous the wave!!!!!!

11. Key facts All waves shorter than visible light can cause cancer.
UV - light - sun burn and skin cancer
X-rays can cause cancer (that is why the dentist leaves the room when she X-rays your teeth)
Gamma rays are the most dangerous – they can kill ALL living things and cause cancer.
We are bombarded by gamma rays coming from the sun every day!

13. Digital and Analogue Signals
Using optical fibres

14. Using optical fibres
Light and infrared radiation can be sent down an optical fibre.
One optical fibre cable can carry telephone calls at the same time!

15. Using optical fibres Advantages of optical fibres
Light can travel round corners in an optical fibre. So unlike a microwave transmission it is not restricted to travelling in a straight line.

16. Using optical fibres Advantages of optical fibres
Light passes along an optical fibre with very little energy loss. Unlike a copper cable the signal does not need frequent amplification.

17. Digital and analogue signals

18. Digital and analogue signals
Digital signals can be sent down optical fibres
A digital signal can only have certain values, usually 0 or 1
An analogue signal carries information by continuously changing its amplitude or frequency.

19. Digital and analogue signals
Noise distorts all signals during transmission. It cannot be removed from analogue signals.
Digital signals can easily be restored to their original condition.
This gives digital signals clearer sound and pictures.

20. Digital and analogue signals
A CD is a digital recording system.

21. Digital and analogue signals
A vinyl record is an analogue recording system.