Reflection and refraction
Reflection
Waves reflect from surfaces. The Angle between the normal and the incident ray. equals the The angle between the reflected ray and the normal (the imaginary line drawn at 90 degrees to the reflecting surface).. This is called the law of reflection. So, if a wave hits a mirror at an angle of 36°, it will be reflected at the same angle (36°).
An incident ray of light hits a plane mirror at an angle and is reflected back off it. The angle of reflection is equal to the angle of incidence. Both angles are measured from the normal. The normal is an imaginary line at right angles to the plane mirror.
Make sure that you can label the normal, angle of incidence and angle of reflection on a diagram of reflection.
Refraction
Waves change speed when they pass across the boundary between two different substances, such as light waves refracting when they pass from air to glass. This causes them to change direction and this effect is called refraction.
Water waves refract when they travel from deep water to shallow water (or vice versa).
Why does refraction happen?
Refraction happens because the speed of the wave changes.
Light travels slower (compared to its speed in air) in a more dense material like glass. The wavelength will also decrease in order to keep the frequency constant.
Water waves travel slower in shallower water. The wavelength will decrease in order to keep the frequency constant.
Changes in wavelength are When two quantities have the same ratio or relative size. For example, current is proportional to voltage if the current doubles when the voltage is doubled. to changes in wave speed. The frequency doesn’t change.
Note that refraction doesn't happen if the waves cross the boundary at an angle of 90° (called the normal). In this case, they carry straight on.
When light passes from air into a block of glass the following is seen.
Image caption, The wave's properties change as it enters the glass, then return to their original values when the wave leaves the glass
1 of 3
If the angle of incidence is big enough, the light will not escape from the block – it will be totally internally reflected. You can learn more about this in the total internal reflection guide.