LIGHT Reflection and Refraction

Mirrors and highly polished opaque surfaces reflect light in predictable ways.

These are additional major points to take from the previous diagram… – The angle of incidence = the angle of reflection – The incidence ray, the normal and the reflected ray always lie in the same plane – These two statements make up the laws of reflection!!!!

The Refraction of Light Refraction is different from reflection in that it is “the change in direction of light as it passes through from one medium into another of differing density”.

The angle of incidence is the angle between the incidence ray and the normal. The angle of reflection is the angle between the reflected ray and the normal. The ANGLE OF REFRACTION IS THE ANGLE BETWEEN THE REFRACTED RAY AND THE NORMAL

In the previous diagram what was shown was partial reflection and refraction. Where a beam of light splits into two rays… one is reflected the other is refracted. When the ray goes from air to glass, the ray bends towards the normal, so the angle of refraction is less than the angle of incidence.

When the light passes from glass to air, the refraction ray bends “away” from the normal, thus the angle of refraction is greater than the angle of incidence.

Index of Refraction Light bends when it passes through different mediums due to the fact that the speed of light changes. This has to do with the type of material the light is passing through. All are compared to the travelling of light through a vacuum (i.e. space) because that allows for the fastest speed of light.

Points to Ponder Low n to high n, light bends towards the normal. – Air to glass High n to low n, light bends away from the normal. – Glass to air If a light is shone down the normal there is no refraction.

Index of Refraction Vacuum = 1 Air = Water = 1.33 Pyrex = 1.47 Diamond = 2.42

Snell’s Law The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. n 1 sin θ 1 = n 2 sin θ 2

Application of Snell’s Law A beam of light in air (n=1.00) strikes a water surface (n=1.33) with an angle of incidence of 30 o. What is the angle of refraction in the water?

Critical Angle & TIR Critical Angle – Refracted ray of light bends to be 90 o from the normal and travel as a ray along the separation point of the two mediums. TIR – Total Internal Reflection – Any angle of incidence above the critical angle will result in total internal reflection in which case the light will stay within the medium and be reflected.

Critical Angle & TIR