Light & Geometric Optics

1. Light & Geometric Optics • In this unit: • Properties of light • Colours • Production of light • Reflection of light • Refraction of light • Lenses and optical devices • The eye

2. What is light? • A form of energy that the Sun emits in all directions

3. Laser Part 1 – Properties of Light Light travels in straight lines:

4. At this speed it can go around the world 7.5 times in one second. Light travels VERY FAST – around 300,000, 000 metres per second. (3.0 x 108 m/s)

5. Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang. Light travels much faster than sound. For example:

6. Homework We see things because they reflect light into our eyes:

7. Rays of light Shadows are places where light is “blocked”: Shadows

8. Light transfer • Light energy is transferred through radiation • RADIATION • A method of energy transfer that doesnot require a medium • MEDIUM • Any physical substance that acts as a carrier for the transmission of energy

9. Light is an electromagnetic wave

10. Electromagnetic spectrumtravels as waves and transfers energy from one place to another. All electromagnetic waves can travel through a vacuum, and they all travel at the same speed in a vacuum. The electromagnetic spectrum is a continuous range of wavelengths. The types of radiation that occur in different parts of the spectrum have different uses and dangers, which depend on their wavelength and frequency.

12. Radio waves • Low energy waves with long wavelengths • Includes FM, AM, radar and TV waves • Low frequency • Used in many devices such as remote control items, cell phones, wireless devices, etc.

13. Microwaves • Shorter than radio, longer than light and infrared • First used in radar, now used in communication, medicine and consumer use (microwave ovens)

14. Infrared light • Invisible waves that are detected as heat • Can be detected with special devices such as night goggles • Used in heat lamps, remote controls, lasers • Higher energy than microwaves but lower than visible light

15. Visible Light • The portion of the electromagnetic spectrum that human eyes can detect • ROYGBIV (red, orange, yellow, green, blue, indigo, violet) • Red is the lowest frequency and violet is the highest frequency

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

17. X-Rays • Medical imaging (i.e. used for teeth and bones) • Security equipment (i.e. luggage scanners) • High energy waves • Can cause cancer

18. Gamma rays • Highest energy • Generated by radioactive atoms and in nuclear explosions. • Can kill living cells • Gamma rays are used to kill cancerous cells. • Blocked from Earth’s • surface by atmosphere

19. The Electromagnetic Spectrum

20. SOURCES OF LIGHT • There are several ways to produce light. Each method involves the conversion of another type of energy into light energy.

21. Light from Incandescence Light is produced from heating the object This bulb has a thin wire filament, usually made of tungsten, that glows as electricity passes through it. Only 5 to 10 % of the electricity is converted into visible light, so the bulb is inefficient as a light source. Modern Incandescence Light Bulb

22. Light from Electric Discharge Produce by passing an electric current through a gas. The electricity causes the gas to glow. Lightning Neon Light

23. Light from Phosphorescence Materials with phosphors absorb ultraviolet light and give off some of it as visible light of lower energy over varying periods of time. Glow –in-the-Dark toy

24. Light from Fluorescence A material absorbs UV light and immediately releases visible light This bulb make use of both electric discharge and fluorescence. When the light is turned, on the electric current causes the mercury atoms to emit ultraviolet light. This ultraviolet light then strikes the fluorescent inner surface producing visible light immediately. A fluorescent light bulb

25. Light from Fluorescence Fluorescent lights are 4 to 5 times more energy efficient than incandescent bulbs. CFLs - Compact fluorescent light

26. Light from Chemiluminescence A chemical reaction produces light directly Light sticks operate by causing two chemical to mix. One in a glass tube and the other in the main body. When the stick is bend the glass is broken and the two chemicals are mixed. The chemical reaction produces visible light with little on no heat. Light stick or glow stick

27. Light from Bioluminescence An organism releases light through a chemical reaction in its body Occurs in bacteria, fungi, fish glow-worms and fire flies etc. In fire flies, oxygen is combined with luciferase in the lower abdomen to produce visible light. Bioluminescence is used in insects to protect them from prey, to lure preys, or to attract mates. A fire fly

28. Light from Bioluminescence

29. Light from Bioluminescence Glowing mushroom http://www.ted.com/talks/lang/en/edith_widder_the_weird_and_wonderful_world_of_bioluminescence.html

30. Light from Triboluminescence This is the production of light when certain crystals are scratched, crushed, or rubbed. Rubbing two quartz crystals

31. Light from Light-Emitting Diode (LED) The use of semiconductors such as silicon allows LED to pass electric current in only one direction. LED is different from an incandescent bulb in that: It does not require a filament, It does not produce much heat, It is more energy efficient LED Christmas lights

32. THE LASER – A SPECIAL TYPE OF LIGHT • Light from a laser has special properties. • A laser produces electromagnetic waves of exactly the same energy level • This results in visible light being of a very pure colour • A red laser light entering a triangular prism will still look red on exit • Laser light is also very intense because the electromagnetic waves travel in the same direction and are exactly in unison • Never look directly at a laser beam