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In a concave mirror, an object is placed...

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

A

`x_1x_2`

B

`x_1 +x_2`

C

`x_1//x_2`

D

None of these

Text Solution

Verified by Experts

The correct Answer is:
D
`u = f + x_1`
`v = f + x_2`
`f = uv//(u + v)`
or `f = ((f + x_1)(f + x_2))/((f = x_1)+(f + x_2))`
or `f_2 = x_1x_2`
`therefore f = sqrt(x_1 x_2)`
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