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

Reflection in action

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

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

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

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

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

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

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.

Refraction

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

The mug trick!

The mug trick! Pt2

Water Waves Water waves travel slower in shallow water

Sound Waves Sound travels faster in warmer air

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

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

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

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

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

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

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

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

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.

Diffraction in action

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

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

Diffraction 4

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

Diffraction of radio waves                                                                                                                                                                                                                                                                     Diffraction 6 Diffraction of radio waves