Question

When the physics teacher has given a task to determine the focal length of a concave mirror a clever boy in the class focussed the mirror to a distant object. He moved the screen in front of the mirror and caught a real image on a screen at a distance of 20 cm from the mirror and he determined the focal length. Where should the object be place so that the object and the image are formed at the same position?​

Answer 1

Answer:

$the \: position \: will \: be \: 40 \: cm \:$

Answer 2

Explanation:

As the obtained image is a real image so it is a convex lens.

Image is formed at the focus of the mirror as the object is far away. As object distance u is same in both the cases and image distance for mirror having focal length F2 is increasing as the student is moving the lens away from the screen.

Therefore, focal length of second lens F2 will be more as compared to focal length of F1.

I think it helps you a lot