# Physics

posted by .

A large fish tank is filled with water (of refractive index 1.33). One side of the tank is made of a parallel-sided piece of glass. A ray of light strikes the glass from the outside at an angle of incidence of 48.

Estimate the angle through which this ray is deviated as it emerges into the water. Just give the magnitude of the deviation, there's no need for signs.

• Physics -

Estimate? 10 degrees.

Why not calculate it?

• Physics -

I don't know how to calculate it, that's why I was looking for help

• Physics -

Because the glass side wall is plane-parallel, Snell's law takes the form
N1*sinA1 = N2*sinA2 = N3*sinA3, where
N1 = index in air = 1.00: A1 is angle of incidence in air = 48 degrees
N2 = refractive index in glass = ?
N3 = refractive index in water = 1.33; A3 = angle of emergence (relative to normal) in water.

You can ignore what happens in the glass and write:
1.33*sinA3 = 1.00*sinA1
SinA3 = 0.559
A3 = 34.0 degrees

Angle of deviation (air to water)
= A1 - A3 = 14.0 degrees