A ray of light is incident on a plane reflecting surface at an angle of 30°. Find the deviation in the incident ray. What will be the deviation if the ray suffers a reflection again at a surface inclined at 60° to the first surface?
Answer & explanation
Correct answer: option 4
$∠B'CM_2 = 60°, ∠M_2CD = 60°, ∠B'CD = 120° = D_2, ∠DCN_2 = ∠N_2CB =30°$
$∠ABN_1 = ∠N_1BC =30°; ∠CBA' = 120° = D_1$
The incident ray of light AB on the first mirror M1 at an angle of incidence of 30° is reflected along BC at an angle of reflection 30°.
∴ Deviation in incedent ray = 60° + 60° = 120°
The reflected ray BC is incident on the second mirror M2.
Since $∠M_1OM_2 = 60° , ∠BCO = 60°$,
$∴ ∠BCN_2 = ∠N_2CD = 30°.$
∴ Deviation D2 of the ray = 60° + 60° = 120°
∴ Total deviation due to the two mirrors = $D_1 + D_2 = 240°$
