The Nature of Light

3. Laser The Nature of Light 1. Light travels in straight lines:

4. 2. Light travels VERY FAST – around 300,000, 000 metres per second.(that’s about 1 billion km/h !) At this rate it can go around the world 8 times in one second.

5. The sun is about 150 million km (1.5 x 1011 metres) away. How long do you think it takes for its light to reach us? about 500 s or 9 1/2 minutes!

6. The next closest star is Alpha Centauri at 41.5 trillion km away (4.15 x 1016 m) • Therefore it takes over 4 years for its light to reach Earth! • There are stars (that we know about) whose light takes millions of years to reach us. So when we look at them we are seeing the star as it existed millions of years ago.

7. Thunder and lightning start at the same time, but we will see the lightning first. Light travels much fasterthan sound! Examples... 2) When a starting pistol is fired we see the smoke first and then hear the bang.

8. 3. Light energy is a form of radiation RADIATION • A method of transferring energy that doesnot require matter (atoms and molecules) This is why light energy can travel through space where there is no matter. The sun’s light reaches the Earth!

9. 4. Light is an electromagnetic wave • Light has both electric and magnetic parts which vibrate thus making waves. • The wave travels at the speed of light.

10. Light waves behave like water waves. The water itself does not pile up on the beach. But the energy of the waves moves against the beach.

11. 5. Other types of radiation • We use the electromagnetic spectrum as a classification system. • Visible light is just one type of radiation – the only one our eyes can see.

12. The shorter the wavelength, the higher the energy of the wave … and the more work or damage it can do.

13. Colours • White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. • ROYGBIV(red, orange, yellow, green, blue, indigo, violet) • Red is the longest wavelength and violet is the shortest wavelength

15. Radio waves • Low energy waves - long wavelengths • FM, AM, radar and TV waves • Remote control items, cell phones, wireless devices, etc.

16. Microwaves • First used in radar, now used in communication, medicine and consumer use (microwave ovens)

17. Infrared light • Invisible waves that are detected as heat • Can be seen only with special devices such as night goggles • Used in heat lamps, remote controls, lasers

18. Ultraviolet waves • Higher energy than visible light waves • Causes skin to tan and burn • Can cause skin cancer and blindness in humans • Used in tanning beds and sterilizing equipment

19. X-Rays • Medical imaging (teeth and bones) • Security equipment (i.e. luggage scanners) • High energy waves (short wavelength) • Can cause cells to become cancerous

20. Gamma rays • Highest energy (shortest wavelength) • Can be generated in nuclear explosions. • Will kill living cells • Gamma rays are used to kill cancerous cells (radiation treatment). • Blocked from Earth’s surface by atmosphere

21. What Happens to Light When it Encounters Matter? • 1. Transmitted • transparent substances such as clear glass • light waves pass right through. • (note – there is no substance that is perfectly transparent, but many are very close!)

22. 2. Reflected - reflective substances are at which light waves strike the surface and 'bounce' back.

23. 3. Absorbed • the energy of light is converted by the substance into some other form of energy (often heat).

24. - opaque substances are those through which no light is able to pass through. Therefore, nothing can be seen through them. • - translucent substances are those through which some light passes, but objects cannot be seen clearly because the light is scattered in different directions.