1. How is light reflected from a mirror?
Normal
Incident Ray
Reflected Ray
Angle of Incidence
Angle of Reflection
Plane Mirror
Angle of incidence = Angle of reflection

2. Reflection in action

3. Is there a law to explain reflection?
Angle of incidence = Angle of reflection
500
500

4. Regular Reflection
Smooth, shiny surfaces like mirrors give ‘regular’ reflection

5. Diffuse Reflection
Rough, dull surfaces like a table top give ‘diffuse’ reflection. This is where light is scattered in all directions.

6. Wave Properties (1) 1. Reflection
Waves will bounce off a surface under certain conditions
eg the surface must be shiny for electromagnetic waves
Reflective surface
Incident Ray
Reflected Ray

7. Angle of Incidence = Angle of Reflection
Wave Properties (2)
Normal
Angle of Incidence
Angle of Reflection
Angle of Incidence = Angle of Reflection

8. What ‘type’ of reflection can you see?
Diffuse reflection
Regular Reflection

12. Images in a Plane Mirror
Properties of images in plane mirrors, they are;
Upright (i.e. the same way up as the object)
Virtual (i.e. cannot form on a screen like a movie)
Same size as object
Laterally inverted (i.e. the left of the object looks to be the right of the image)
Distance of the object from the mirror is equal to the distance of the image from the mirror.
A line joining a point on the object to its reflection on the image is perpendicular to the mirror.

15. Refraction

16. Refraction
Waves cross a boundary causing a change in speed and consequently wavelength
Depends on the refractive index of different substances
Glass Block
Air
Normal
All waves can be Refracted.
Refraction is a change of direction due to a change of speed.
The example I used involves light rays hitting a glass block. Glass is a medium which is more dense than air. so the light will travel more slowly within the glass block than it would do in air. As the light ray crosses the boundary from one medium to another, it bends. 16

17. The mug trick!

18. The mug trick! Pt2

19. Water Waves
Water waves travel slower in shallow water

20. Sound Waves
Sound travels faster in warmer air

21. Light Waves
Light slows down as
it goes from air to
glass/water

22. Refraction 1
When a wave changes speed (normally when entering another medium) it may refract (change direction)

23. Refraction 2
The wavelength changes, the speed changes, but the frequency stays the same

24. Refraction 3
There is a relationship between the speed of the wave in the two media and the angles of incidence and refraction i r
Ray, NOT wavefronts

25. Refraction 4
speed in substance 1 sinθ1
speed in substance 2 sinθ2 =

26. Refraction 5 n = c cm In the case of light only, we usually define a
quantity called the index of refraction for a
given medium as below:
where c is the speed of light in a vacuum
and cm is the speed of light in the medium
n = c cm

27. Refraction 6
Thus for two different media
sinθ1/sinθ2 = c1/c2 = n2/n1

28. Refraction 7
When the wave enters at 90°, no change of direction takes place.

29. Diffraction
Occurs when waves pass through a gap or around an object of roughly the same size or smaller than their wavelength.
Large gap - the middle parts of the waves go straight through the gap, with a slight curving at the edges of the waves.
Small gap - if the gap is smaller than the wavelength of the waves, the waves fan out in circles.

30. Diffraction in action

31. Diffraction 2
Diffraction is most when the opening or obstacle is similar in size to the wavelength of the wave

33. Diffraction 3
Waves spread as they pass an obstacle or through an opening

34. Diffraction 4

35.                                                                 
                                                                
                                                                
                                                                
Diffraction 5
That’s why we can hear people around a wall but not see them!

36. Diffraction of radio waves
                                                                
                                                                
                                                                
                                                                
Diffraction 6
Diffraction of radio waves