Two mirrors are inclined at an angle 8 as shown in the figure, Light r

1.	Two mirrors are inclined at an angle 8 as shown in the figure, Light ray is incident parallel to one ofmirrors. Light will start retracing its path after third reflection if:
Answer» Let MN and MP are two plane mirrors be inclined at an∠PMN=θ. A light ray AB parallel to MN is incident on MP and the ray after third reflection on MP at B retraces its path as shown in the diagram. Hence CD is perpendicular to MP. This means∠BCN=∠DCM=90∘−θ.AB\|\|MNand BC is the intercept. So∠PBA=corresponding ∠PMN=θ And∠ABC=180∘−2θ SinceAB\|\|MNand BC is the intercept , then ∠ABC+∠BCN=180∘ ⇒180∘−2θ+90∘−θ=180∘ ⇒3θ=90∘ ⇒θ=90∘3=30∘ Let MN and MP are two plane mirrors be inclined at an∠PMN=θ. A light ray AB parallel to MN is incident on MP and the ray after third reflection on MP at B retraces its path as shown in the diagram. Hence CD is perpendicular to MP. This means∠BCN=∠DCM=90∘−θ.AB\|\|MNand BC is the intercept. So∠PBA=corresponding ∠PMN=θ And∠ABC=180∘−2θ SinceAB\|\|MNand BC is the intercept , then ∠ABC+∠BCN=180∘ ⇒180∘−2θ+90∘−θ=180∘ ⇒3θ=90∘ ⇒θ=90∘3=30∘

Two mirrors are inclined at an angle 8 as shown in the figure, Light ray is incident parallel to one ofmirrors. Light will start retracing its path after third reflection if:

Answer»

Let MN and MP are two plane mirrors be inclined at an∠PMN=θ. A light ray AB parallel to MN is incident on MP and the ray after third reflection on MP at B retraces its path as shown in the diagram. Hence CD is perpendicular to MP.

This means∠BCN=∠DCM=90∘−θ.AB||MNand BC is the intercept.

So∠PBA=corresponding ∠PMN=θ

And∠ABC=180∘−2θ

SinceAB||MNand BC is the intercept ,

then

∠ABC+∠BCN=180∘

⇒180∘−2θ+90∘−θ=180∘

⇒3θ=90∘

⇒θ=90∘3=30∘