Question

In the diagram, a ray of light is incident on a plane mirror at an angle of 30°. Calculate the new angle of
incidence if the mirror is rotaled through 10°.​

Answer 1

Answer:

The light ray is making 30 to the power of 0 with the mirror

Therefore it makes angle i equals 90 to the power of 0 minus 30 to the power of 0 equals 60 to the power of 0 with the normal

and according to the law of reflection

angle i equals angle r

Henceangle r equals 60 to the power of 0

Answer 2

Answer:

Draw a diagram of reflection by a plane mirror.

see, that if mirror is rotated through an angle theta , the reflected ray turns through an angle two times theta.

this is due to the incidence and reflected both angles turning through theta. as the normal to the mirror also rotates.

in the present case

you are rotating the mirror through an angle 30 degrees, so the reflected ray will rotate in the above manner by an angle 60 degrees.

however you have also rotated incidence ray by 10 degree. if it is in the same direction as the turning of mirror , this will reduce the angle of incidence by 10 degree , so the actual rotation of the reflected ray will be reduced by 10 degree,

so finally you will get the reflected ray turned through

60 -10 = 50 degrees.