Question

A beam of light strikes the surface of water at an incidence angle of 60°. Determine the directions of the reflected and refracted rays. For water, n=1.33.

A- (a) 30° reflected into air, (b) 22° refracted into water

B- (a) 60° reflected into air, (b) 41° refracted into water

C- (a) 90° reflected into air, (b) 60° refracted into water

D- (a) 41° reflected into air, (b) 30° refracted into water

Answer 1

Answer 2

The correct answer is B- (a) 60° reflected into air, (b) 41° refracted into water.

When light travels from one medium to another, the angle of incidence (the angle between the incident ray and the normal to the surface) is equal to the angle of reflection (the angle between the reflected ray and the normal), and the ratio of the sines of the angles of incidence and refraction is equal to the ratio of the velocities of light in the two media. This is known as Snell's law.

Using Snell's law, we can calculate the angle of refraction:

sin(60°)/sin(90°) = 1.33/1

sin(r)/sin(90°) = 1/1.33

sin(r) = sin(90°)/1.33

sin(r) = 0.7519

r = sin^-1(0.7519)

r = 48.93°

So the refracted ray makes an angle of 48.93° with the normal.

The angle of reflection is equal to the angle of incidence, so the reflected ray makes an angle of 60° with the normal.