Value Of Focal Length Of A Spherical Mirror. (Concave Mirror).

Q14. Describe an activity to find the appropriate value of focal length of a spherical mirror. (Concave Mirror).
Ans. Hold a concave mirror in your hand and face its reflecting surface towards the sun. Near to the mirror keep a sheet of paper. Adjust the mirror, such that the sunlight reflected by the concave mirror falls directly on the sheet of paper placed to near it. Move the sheet of paper forward or backward until a bright spot of light is produced on the sheet of paper. This is spot of light is the tiny real inverted image of the sun on the sheet of paper. This point is the focus of the mirror. Measure the distance of this image from the position of the mirror which is equal to the focal length of the mirror.

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