Question

a student holding a mirror in his hand, directed the reflecting surface of the mirror towards the sun. He then directed the reflected light on to a sheet of paper held close to the mirror.
(a) What should he do to burn the paper?
(b) Which type of mirror does he have?
(c) Well he be able to determinethe approximate value of focal length at this mirror from this activity? Give reason and draw a ray diagram to justify your answer in this case.

Answer 1

Answer

(a) What should he do to burn the paper?

• In order to burn the paper, it must be placed at the focus of the mirror

(b) Which type of mirror does he have?

• If he wanted to burn the piece of paper then it must be a converging lens so that the light that's falling on the mirror gets converted into the paper allowing the heat to burn it

(c) Will he be able to determine the approximate value of focal length at this mirror from this activity

Diagram has been attached

• Yes, he will be able to determine the approximate focal length this way, because the paper will only burn if enough light is converge at a single spot and the only point where parallel rays from the sun gets converged is at the focus
• So finding the point where the paper should be placed in order to burn the paper is the same as finding it's approximate focal length