An object is placed 20 cm in front of a plane mirror. The mirror is moved 2 cm towards the object. The distance between the positions of the original and final images seen in the mirror is : (a) 2 cm (b) 4 cm (c) 10 cm (d) 22 cm

1. We know that distance of the object from plane mirror is same as distance of the image from plane mirror.
2. As the object was initially placed 20 cm in front of the plane mirror, the image formed was 40 cm away from the original object.
3. Now, when the mirror is moved 2 centimeters towards the object, the image also moves towards the object.
4. So now distance of object from mirror is 18cm $\therefore$ distance of image from mirror is also 18cm.
5. In this perspective, the distance of the image from the object will be 18+18 = 36 cm
6. So, distance between the original and final images = 40 cm - 36 cm = 4 cm