Light

1. Light In this Unit you will learn: • Light is form of energy • Properties of light • Laws of reflection reflection • Understand how to locate an image by no parallax • Lateral inversion • How images are formed in plane mirrors • Uses of plane mirrors

2. Keywords

3. Light is form of energy • Light can do work eg. Crookes radiometer • Light can be converted to other forms of energy e.g. Solar cell, light to electricity. (show demo model of this) • Other forms of energy can be converted to light e.g. Fire.

4. Laser Part 2 – Properties of Light Light travels in straight lines:

5. Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

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

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

8. A luminous object is one that produces light. A non-luminous object is one that reflects light. Name 3 luminous sources of light and 3 reflectors Luminous and non-luminous objects Luminous objects Reflectors

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

10. Properties of Light summary • Light is a form of energy • Light travels in straight lines • Light travels much faster than sound • We see things because they reflect light into our eyes • Shadows are formed when light is blocked by an object

11. Reflection The bouncing of light of an object is called reflection A straight líne showing the direction in which the light is travelling is called a light ray Beams of light can be coverging, diverging or parallel.

12. Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

13. Reflection Normal Reflection from a plane mirror: Reflected ray Incident ray Angle of reflection Angle of incidence Mirror

14. Incident ray, reflected ray and normal lie on the same plane Angle of incidence = Angle of reflection The Laws of Reflection In other words, light gets reflected (bounced) from a surface at ____ _____ angle it hits it. The same !!! Normal

15. How an Image is formed in a plane mirror • The image is located ón the perpendicular form the object to the mirror. • The image is the sames distance behind the mirror as the object is in front of the mirror.

16. Experiments • To demonstrate the laws of reflection using a plane mirror. • To locate an image in a plane mirror the method of no parallax

17. Lateral Inversion Lateral inversion is where the left of an object appears to the right image and vice versa.

18. Real and Virtual images A virtual image is an image formed by th apparent intersection of light rays.

19. Use of plane mirrors Two examples: 2) looking at yourself 1) A periscope

20. Using no parallax to find an image The apparent relative motion of the two pencils due to the motion of the observer is called parallax In diagram (b) there is not apparent relative motion of the pencils due to the motion of the observer, this is called no parallax