While performing the experiment to determine the focal length of a convex lens by using the sun as the distant object, a student could not find a screen with stand. In the absence of a good screen, which of the following method is the most appropriate and safe to be used by the student?
(1) He should focus the image of the sun on his hand
(2) He should focus the image of the sun on his nylon shirt
(3) He should focus the image of the sun on a wall of the room
(4) He should focus the image of the sun on a carbon paper

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Solution

Sun is very far from the earth, so all the rays coming from the sun become parallel and when they fall on a convex lens, they converge at its focus to form a diminished image. So, if the image would be obtained on either of a hand, nylon shirt or a carbon paper then due to focussed light energy on a single point, the temperature may increase and it can start a fire too. That's why, to avoid any damage or harm, the image of the sun should be obtained on a wall of the room.

Hence, the correct answer is option 3.

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