Question

Q8. Which statement is true for the reflection of light?

a) The angle of incidence and reflection are equal.

b) The reflected light is less bright than the incident light.

c) The sum of angle of incidence and reflection is always greater than 90°.

d) The beams of incident light after reflection diverges at unequal angles.​

Answer 1

Answer:

option .a

angle of incident= angle of reflection

Answer 2

The statements (A) angle of incidence is equal to angle of reflection and (B) The reflected light is less bright than the incident light are true for the reflection of light

Explanation:

For a ray of light, incident on a flat surface that makes an angle ∠$i$ with the normal gets reflected at the surface and becomes the incident ray that makes an angle ∠$r$ with the normal, the laws of reflection are given as follows.

• The angle of incidence made by the incident ray with the normal is always equal to the angle of reflection made by the reflected ray with the normal.                        

                                            ∠$i$ = ∠$r$  

• The angle of incidence, the angle of reflection and the normal at the point of contact of the incident ray and reflected ray, all lie in the same plane.

Now, According to the question,

• The angle of incidence and reflection are equal.

True, Because, As per the first law of reflection, the angle of incidence is equal to the angle of reflection.

• The angle of incidence is less bright than the incident ray.

True, The incident ray on touching the surface of reflection, a number of phenomenons occur.

Firstly, the reflection, that is the incident ray gets reflected and becomes the reflected ray.

Secondly, refraction occurs, that is some part of the incidence is sent as the reflected ray but, a small part of it becomes the refracted ray and enters the material of the surface.

This division of energy of the incident ray into 2 parts is the reason that the reflected ray is less brighter than the incident ray.

• Sum of angle of incidence and reflection is always greater than $90^{o}$

False. Because, If we see the ray diagram attached below,

The normal makes an angle of $90^{o}$ with incident as well as reflected ray.

We have, ∠$AON=i$   and  ∠$BON=r$

Since, $i=r$ ,

∠$AON=$ ∠$BON$

Now, since the reflecting surface is flat, the sum of all angles will be $180^{o}$and therefore, the angles ∠$AOP$ and ∠$BOQ$ will also be equal.

∠$AOP$ $+$ ∠$AON+$ ∠$BON+$ ∠$BOQ=180^{o}$

Therefore,

$4$ ∠$AON=180$

∠$AON=45^{o}$

Hence, ∠$AOB =2$∠$AON$ $=90^{o}$

Hence, $i+r=90^{o}$

The sum of angle of incidence and angle of reflection is equal to $90^{o}$ and not more than it.

• The beams of incident light after reflection diverges at unequal angles.

False, For an even surface that does not contain any deformity, the beams do not diverge at unequal angles.