Question

a mirror forms an image of 15cm high object on a screen placed 5 cm away from the mirror the height of the mirror is 40 cm find the focal length of mirror and distance between the mirror and the object
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Answer 1

Explanation:

H₁ = 15 cm , v = -5 cm , H₂ = 40 cm

Since, -v/u = H₁/H₂

or 5/u = -40/15 (because the image is inverted)

or u = -5 x 15/40 = -15/8 cm

⇒ 1/v + 1/u = 1/f  or  1/-5 + (-8/15) = 1/f

or f = -15/11 = -1.36 cm

So, the focal length is 1.36 cm

and the mirror is concave