Snell's law

The ratio of the sines of the angles of incidence and refraction as light passes across the interface from one medium to another is a constant. Note: the angle of incidence is the larger of the two angles (in air).

sin i / sin r = n

The constant n is called the refractive index of medium 2 (glass) with respect to medium 1 (air).

When light passes from one medium that is not air to another (from water into glass) Snell's law becomes ...

sin i / sin r = ng/nw

Angle i is the larger of the two angles (in the water). The formula is easy to remember by noting that the refractive index of air is 1 and Snell's law for glass in air is ...

sin i / sin r = ng/1

 

Questions

1 Mark the angles of incidence and refraction on the diagrams.

2 Find the unknown angles.

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3 Find the critical angle for total internal reflection for ...

... glass in air ...

... water in air ...

 

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... and for glass in water.

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4 Find the unknown angles.

 

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Comment on the angle at which the ray emerges from the bottom surface.

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