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Mirror and Magnification Formula Problems
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An object is placed at a distance of 1.5 m from a screen and a convex lens is interposed between them. The magnification produced is 4. The focal length of the lens is then
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A
0.24 m
💡 Explanation:
Here, $m =\dfrac{v}{u} =-4$
$\Rightarrow u = \dfrac{-v}{4}$------------(1)
Also, $|u| + |v| = 1.5$
$\dfrac{v}{4} + v = 1.5$
$\Rightarrow \dfrac{(v+4 v)}{4} = 1.5$
$\Rightarrow v = 1.2 m$
So, putting the value of $v$ in equation (1):
$u= \dfrac{-1.2}{4} = -0.3 m,,,$
$\therefore f =\dfrac{uv}{u-v}$
$\Rightarrow f=\dfrac{(-0.3 \times 1.2)}{(-0.3 - 1.2)} = 0.24m$
Hence the correct option is $(C)$