Question

If the glancing angle of incidence is ${{30}^{\circ }}$ , what will be the angle of incidence?
A. ${{30}^{\circ }}$
B. ${{60}^{\circ }}$
C. ${{90}^{\circ }}$
D. ${{150}^{\circ }}$

Answer 1

Hint: The glancing angle of incidence is given and we know that , the plane and the normal makes an angle of ${{90}^{\circ }}$. We see when the incidence ray is incident on the plane it makes two angles one with the normal and another with the plane, the angle that the incident ray makes with the normal is the incidence angle and the angle which the incident ray makes with the plane is the glancing angle.

Formula used:
Angle of incidence + glancing angle of incidence = ${{90}^{\circ }}$

Complete step-by-step answer:

Here, in the above diagram we can see that a ray of light is passing from one medium to another. The angle that the incident ray is making with the normal is incidence angle and the angle that the incident ray is making with the plane is known as glancing angle as shown in the figure.

The angle between the incident ray and reflecting surface is known as the glancing angle of incidence.
Hence,
We can say that,
Angle of incidence + glancing angle of incidence = ${{90}^{\circ }}$
So,
We know that the glancing angle of incidence is ${{30}^{\circ }}$.
Angle of incidence + ${{30}^{\circ }}$= ${{90}^{\circ }}$.
Angle of incidence = ${{90}^{\circ }}$ - ${{30}^{\circ }}$
Therefore, Angle of incidence = ${{60}^{\circ }}$

So, the correct answer is “Option B”.

Additional Information: Any ray that strikes a surface is known as incident ray.
Refracted ray is a ray that helps us to know the direction that the light takes after changing from one media to another.

Note: Students generally confuse between the glancing angle of incidence and the incident angle they must take a note on it. Students must try to draw and solve the question to make sure there are no errors.