The electro-magnetic spectrum

1. The electro-magnetic spectrum

3. Key facts • All the waves travel at the same speed – around 300 000 km/s

4. Key facts • All the waves travel at the same speed – around 300 000 km/s • All the waves are transverse waves

5. 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

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

7. Key facts • 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 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 40 000 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.