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 bum the paper?(b) Which type of mirror does he have?(c) Will he be able to determine the approximate value of the focal length of this mirror from this activity? Give reason and draw ray diagram to justify your answer in this case.

 (a) To burn the paper student should move the mirror in such a way that the paper is positioned at the focus of the mirror.

(b) Student has a converging type of mirror that is concave mirror.

(c) Yes, he can measure the approximate value of focal length from this activity as the paper will burn when it will be kept at the focus of the mirror, as shown in the figure given below:

Explanation

A concave mirror converges a parallel beam of light coming from a distant object onto the focus $(F)$. In other words, a concave mirror forms a real, inverted, and highly diminished image of an object at focus, when the object is at infinity.

Thus, light rays coming from the distant object i.e, the sun, converges at the focus $(F)$ of the concave mirror and forms a real, inverted, and diminished image of the sun. Since, these light rays have heat energy, which is when focused on a point of paper to create a sharp image of the sun, causing heat to increase at that point. Thus, the paper gets burnt on that point and leaves a hole.

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Updated on: 10-Oct-2022

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