11yup harrys answer is correct
Q.1. A man uses a concave mirror for shaving.He keeps his face at a distance of 25 cm from the mirror and gets an image which is 1.4 times enlarged.Find the focal length of the mirror.
Q.2.Find the diameter of the image of the moon formed by a spherical concave mirror of focal length 7.6m.The diameter of the moon is 3450km and the distance between the moon and the earth is 3.8 x 105 km.
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7 Answers
1I had solved this problem in such a large span of time on my own.But you have not given the solution.The answers I also have.
1FOR CONCAVE MIRROR (virtual image)
u=+ve v=-ve we have to find f
m=h'/h=-v/u
=> 1.4x/x=-v/25
=> 14/10.25=-v
=> v=-35cm
by mirror formula;
1/v+1/u=1/f
=> -1/35+1/25=1/f
=> 1/f= -2/175
(f=-ve for concave mirror)
hence
f=-175/2