Question

By what angle should m2 be rotated so that the light ray after reflection from both the mirrors become horizontal

Answer 1

By 5⁰ anticlockwise and 95⁰ clockwise M₂ should be rotated so that the light ray after reflection from both the mirrors become horizontal.

Refer the attached figure for the ray diagram

Angle of reflection from mirror M₁ = 50⁰

According to the question ray should make the same angle with M₂ for the ray to become horizontal.

But M₂ is tilted by 25⁰

So, angle of incidence with respect to M₂ = 50⁰ + 25⁰ = 75⁰

Now if the ray is horizontal then the angle between the emerging ray and the mirror M₂ will be = 90 -25 = 65⁰

So the mirror has to be rotated by

= (75 - 65)/2

= 5⁰ anticlockwise and 95⁰ clockwise

Answer 2

Refer the attached figure for the ray diagram

Angle of reflection from mirror M₁ = 50⁰

According to the question ray should make the same angle with M₂ for the ray to become horizontal.

But M₂ is tilted by 25⁰

So, angle of incidence with respect to M₂ = 50⁰ + 25⁰ = 75⁰

Now if the ray is horizontal then the angle between the emerging ray and the mirror M₂ will be = 90 -25 = 65⁰

So the mirror has to be rotated by

= (75 - 65)/2

= 5⁰ anticlockwise and 95⁰ clockwise