Question

The angle between incident ray and reflected ray is 80 degree. What is the value

of angle of Incidence?​

Answer 1

According to laws of reflection,

Angle of incidence and angle of reflection is always equal. i.e ∠i = ∠r,  

and he incident ray, the normal at the point of incidence and the reflected ray lie on the same plane.

Here, angle between the incident ray and reflected ray is 80°.

Since, angle of incidence and reflection are equal.. let say them x°.

then, x° + x° = 80°

or, 2x° = 80°

or, x° = 40°

So, angle of incidence = angle of reflection = 40°

Answer 2

Given: angle between the incident ray and reflected ray = 80°

To Find: angle of incidence, ∠i.

Solution:

To calculate ∠i, the formula used:

• the angle of incidence (∠i ) = angle of reflection (∠r)  

• ∠i  = ∠r                                   ⇒ Law of reflection           

   

Applying the above formula:

As the angle between the incident ray and reflected ray = 80°

∠i + ∠r = 80°                              ⇒ 1

Let's consider the angle of incident and angle of reflection as X.

∠i  = ∠r = X                                ⇒ 2

Putting the value X, in equation 1:

X + X = 80

2X = 80

X = 80 / 2

X = 40                                       ⇒3

On comparing equations 2 and 3:

∠i = ∠r = 40°

or, angle of incident, ∠i  =  40°

Hence, the angle of incidence is 40°.