Question

The diagram below shows a light ray striking and reflecting from a plane
mirror. AO is the incident ray and OB the reflected ray. The angle between the
incident ray and the reflected ray is 120°.
(i) What is the value of the angle of reflection?
(ii) If the image of an object is formed 5 cm behind the mirror, what is the distance between the image and the object?
(iii) !f two plane mirrors are used and kept facing parallel to each other, how
many images are formed if the object is kept in between them?​

Answer 1

Answer:

(I) 60

(ii) 5 cm

(iii) infinite

Explanation:

(I) angle of refelction =120 divided by 2 =60 degrees

(ii) image distance = object distance = 5 cm

(iii) if an object is placed between two parallel mirrors then infinite images are formed.

Answer 2

i) $\angle r=60^{\circ}$

ii) object is at 5 cm from the mirror

iii) Infinite

Explanation:

In the given diagram of the question we apply the law of reflection, we have:

i)

$\angle i=\angle r$

where

$\angle r=$ angle of reflection

$\angle i=$ angle of incident

Here

$\angle i+\angle r =120^{\circ}$

$\angle i=\angle r=60^{\circ}$

ii)

In the plane mirror we have the scaling ratio as 1.

So the distance of the object form the mirror when the image is at 5 cm from the mirror will be the same as that of the image. Hence we can say that the object is also at 5 cm from the mirror.

iii)

If the two plane mirrors are parallel to each other then they will keep on reflecting the image of the object between them that will lead to the formation of infinite number of images of the object.

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TOPIC: reflection via plane mirror

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