Question

# In a concave mirror, an object is placed at a distance $$d_1$$ from the focus and the image is formed at a distance $$d_2$$ from the focus. Then the focal length of the mirror is:

A
d1d2
B
d1d2
C
(d1+d2)/2
D
d1/d2

Solution

## The correct option is C $$\sqrt{d_1d_2}$$Let $$f$$ be the magnitude of the focal length of the mirror.Using mirror equation ,$$\dfrac{1}{v}+\dfrac{1}{u}=-\dfrac{1}{f}$$$$\implies \dfrac{1}{-(d_1+f)}+\dfrac{1}{-(d_2+f)}=-\dfrac{1}{f}$$$$\implies f=\sqrt{d_1d_2}$$Physics

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