1. Optics Lesson 2 Absorption, Reflection and Transmission

2. Light Rays A luminous object like a candle radiates light in all directions To show how light is emitted from a source we use light rays A light ray is a line and arrow representing the direction and straight-line path of light

3. Because a candle radiates light in all directions there should be an infinite number of light rays however, you only need to draw a few in all directions to represent this A laser however emits light rays all in the same direction (parallel) – More on lasers later

4. Some Key Terms Geometric Optics – the use of light rays to determine how light behaves when it strikes an object – E.g. reflected back, goes through object, etc. Incident Light – light emitted from a source that strikes an object – E.g. light from the Sun striking the Earth

5. Geometric Optics When light interacts with matter, 3 things can happen. 1.Reflection – Light bounces off the substance 2.Transmission/Refraction – Light changes direction in the new substance 3.Absorption – Light energy is converted to other forms of energy in the material. What types of materials Reflect, Transmit and Absorb light the best??

6. Materials Absorb Light – All Objects Transmit Light – Window Reflect Light – MIrror The reality is that most objects reflect, transmit and absorb light in different ratios. On a glass window for example (30% of light may be reflected 5% absorbed and 65% Transmitted)

7. Light Matter can be classified into three categories depending on how it behaves when light strikes it: 1)Transparent 2)Translucent 3)Opaque

8. Transparent Lets light pass through easily when light strikes it Objects behind are easily seen – E.g. Clear Glass

9. Translucent Allows some light to pass through Does not allow you to see objects behind it clearly – E.g. Frosted Glass

10. Opaque Does not allow any light to pass through All light is either absorbed or reflected It is not possible to see objects behind – E.g. Cardboard, Mirror

11. Lasers

12. Incandescent bulbs vs. Lasers Incandescent bulbs emit light of many energy levels (many colours produced) Lasers produce electromagnetic waves of 1 energy level – Only 1 colour is produced http://www.edumedia-sciences.com/en/a311-prism

13. Incandescent bulbs vs. Lasers Incandescent bulbs shine light in all directions and spread out (infinite light rays) All the electromagnetic waves emitted from a laser travel in mostly the same direction in a very narrow beam – Makes laser light very intense – Why you should never look directly at a laser (even a pen laser)

14. Lasers A high energy laser is so intense and so concentrated that it can be used to burn a hole through steel Also they can be used to measure the distance from the Earth to the Moon with an accuracy of 3 cm. – High energy, narrow beam that doesn’t spread out Lasers Video