Investigating How the Speed of Light Differs in Air and in Perspex

Investigating How the Speed of Light Differs in Air and in Perspex

Planning

Aim: I am going to investigate how the speed of light differs in air

and in Perspex.

Background info: The refractive index is a ratio for working out the

speed of light. The ratio varies for different substances, it

indicates the extent to how light refracts through different

substances. On passing from a less dense medium to a more dense

medium, light is refracted towards the normal, and thus the angle of

incidence, i, is larger than the angle of refraction, r., Willebrord

van Roijen Snell (1591-1626), came up with a law explaining the ratio

of the sine of the angle of incidence to the sine of the angle of

refraction is a constant for any given pair of medium. so a simple

statement of his law is:

sin i / sin r = a constant, n

So in this equation the constant n is equal to the refractive index.

N defines the speed of light in Perspex as a decimal of the speed of

light in air

Example of refractive index values are: water (1.33); perspex (1.49);

window glass (1.51); different glasses (between 1.46 and 1.69); and

diamond (2.42). Diamond has a very high refractive index this is

responsible for it having such a aparkle.

Apparatus

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Lab pack

D-block

Ray Box

Glass lens

Collimator

Prediction

I Predict that the speed of light in Perspex multiplied by the

refractive index of Perspex (1.49) will equal the speed of light in

air.

I am able to draw up a triangle formula for my prediction. (fig 1)

But in our experiment we are shining the ray onto the curved surface

and seeing how light goes from Perspex into air so we will attempt to

work out sin I over Sin R and multiply it by the speed of light in air

to get the speed of light in Perspex.

[IMAGE]fig.