Question

A ray of light falls on a plane mirror making an angel 30® with the mirror. On reflection, the ray deviates through an angel of

Answer 1

as we know the laws of reflection we know that i=r i.e angle of incidence =angle of reflection .

so if the incident ray makes an angle of 30 with the mirror ,so will the reflected ray but on the other side of the normal so the angle of deflection = 60+60 =120

why 60? because the normal is perpendicular to the mirror so the incident and reflected ray will make 60 degree angles each so 60+60( cuz they are on the opposite sides of the normal )

Answer 2

Answer:

The angle of deviation is 120°.

Explanation:

Given the angle of incidence on a plane mirror, $i=30^o$  

As shown in the figure, if the mirror was not there, the ray would have propagated in a straight line.

Because of the mirror the ray reflected back into the same medium.

The angle thus made by the reflected ray deviating its path from straight line is the angle of deviation(d)

According to the laws of reflection, angle of incidence(i) is equal to angle of reflection(r).

The sum of angle of incidence,  angle of reflection and angle of deviation makes a straight angle.

i.e., $i+r+d=180^o$

Since $i=r$, therefore $2i+d=180^o\implies d=180^o-2i$

Substituting the value of angle of incidence,

$d=180-2\times 30=180-60=120^o$

Therefore, the ray deviates through an angel of 120°.