Question

A small object is placed 10 cm in front of a plane mirror. If you stand behind the object 30 cm from the mirror and look at its image, the distance focused for your eye will be:
A. 60 cm
B. 20 cm
C. 40 cm
D. 80 cm

Answer 1

Hint: Here we have to find the distance of the image with respect to the observer which is 30 m in front of the plane mirror that is already given in the question above. The observer is behind the object that is placed at 10 cm in front of the plane mirror. Also here the object is fixed at a point so the image is also fixed.

Complete step by step solution:
We know that when an object is placed in front of a plane mirror, the plane mirror reflects light which helps in forming an image of the object behind the plane mirror and the image thus formed is located at the same distance as the object is present before the plane mirror.

Hence the distance at which the object is placed here d is 10 cm as given in the question.
So the distance at which the image will form at $d$ i.e, 10 cm. Now the observer(we) are at a distance d that is 30 cm from the mirror. So the total distance between the observer and the image will be:
$30\,cm + 10\,cm = 40\,cm$

Hence the correct answer is option C.

Note: Here the observer means we were observing at a distance from a point that is in front of the mirror. If we were behind the mirror then the answer would change. So be careful about the position of the observer, check whether it is in front of the mirror or behind the mirror, also the position of the observer with respect to the object.