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(B) The sun is at infinity,so $u = \infty$. From the mirror formula,$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$.Given $v = -32 \, cm$ (for a concave mir

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$9 \, cm$ above the water level

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(B) The sun is at infinity,so $u = \infty$. From the mirror formula,$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$.Given $v = -32 \, cm$ (for a concave mirror),we have $\frac{1}{f} = \frac{1}{-32} + 0$,so the focal length $f = -32 \, cm$.When the tank is filled with water up to a height of $h = 20 \, cm$,the mirror would have formed an image at $F$ ($32 \, cm$ from the mirror). Since the water level is at $20 \, cm$,the distance of this point $F$ from the water surface is $d = 32 - 20 = 12 \, cm$.This point $F$ acts as a virtual object for the water-air interface. Due to refraction at the plane water surface,the apparent depth $d'$ is given by $d' = \frac{d}{\mu}$.Here,$\mu = \frac{4}{3}$,so $d' = \frac{12}{4/3} = 12 	imes \frac{3}{4} = 9 \, cm$.Since $d'$ is positive,the image is formed $9 \, cm$ above the water surface.

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