Question

Briefly describe how you would find the focal length of a concave mirror quickly but approximately

Answer 1

For an object placed at the focus, the image formed by a concave mirror is at infinity. The image is highly magnified and real. So, we will move the object at a different point and check the image size and the point of formation. The point of focus of the concave mirror will be the point where the image formed is highly magnified and at infinity.