Where should an object be placed in front of | vedclass

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(C) For a concave mirror, the magnification $m$ can be either $+2$ (virtual image) or $-2$ (real image).Given focal length $f = -20\,cm$.The magnifica

Vedclass · Accepted Answer

Both $(A)$ and $(B)$

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(C) For a concave mirror, the magnification $m$ can be either $+2$ (virtual image) or $-2$ (real image).Given focal length $f = -20\,cm$.The magnification formula is $m = \frac{f}{f - u}$.Case $1$: For a virtual image, $m = +2$.$+2 = \frac{-20}{-20 - u_1} \implies -40 - 2u_1 = -20 \implies 2u_1 = -20 \implies u_1 = -10\,cm$.Case $2$: For a real image, $m = -2$.$-2 = \frac{-20}{-20 - u_2} \implies 40 + 2u_2 = -20 \implies 2u_2 = -60 \implies u_2 = -30\,cm$.Thus, the object can be placed at $10\,cm$ or $30\,cm$ in front of the mirror.Therefore, the correct option is $(C)$.

Where should an object be placed in front of a concave mirror of focal length $20\,cm$ so that the image is $2\,times$ the size of the object?

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