Question

A ray of light incidents on a plane mirror as shown in the given figure. Calculate the deviation produced in the ray of light.​

Answer 1

Answer:

Let us draw the image first .

I named that AO , which is the incident ray .

Given ∠MOA = 70° .

So the angle of incidence = ∠MON - ∠MOA

⇒ 90° - 70° = 20°

∠AOM = 20°

Angle of reflection will be equal to angle of incidence .

Angle of reflection = 20° .

Hence ∠NOB = 20° .

Now : ∠BOA = 90° - 20°

⇒ ∠BOA = 70°

Deviation of the path of the incident ray will be :

∠ BOA + ∠ AOC

But again ∠ AOC = ∠ AOM = 70° .

So deviation = 70° + 70°

⇒ Deviation = 140° .

Deviation is the difference between the original path and the reflected path . Basically the difference between where the ray should have gone without reflection and where it has gone after reflection .

Answer 2

Answer:

140°

Explanation:

From the diagram ,

The ray of light was coming from point I and was going towards D. But there was a plane mirror MM` placed between the path of light. So, the light deviated from its path and went along R instead of D after reflection from the plane mirror.It suffered a deviation of angle theta.

NO is normal to the point of incidence.

So ,angle NOM = 90°

and angle IO = 70° ( given )

So, angle ION i.e angle of incidence = 90-70 = 20°

And angle of deviation = 180° -2i = 180 - 2(20°)

= (180-40°)°

= 140° ( Answer)