An empty tank has a concave mirror at its bot | vedclass

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(B) The sun is at infinity, so $u = \infty$.The light is focused at a height $v = 32 \,cm$ from the mirror. Using the mirror formula:$\frac{1}{f} = \f

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$9 \,cm$ above water level

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(B) The sun is at infinity, so $u = \infty$.The light is focused at a height $v = 32 \,cm$ from the mirror. Using the mirror formula:$\frac{1}{f} = \frac{1}{v} + \frac{1}{u} = \frac{1}{32} + \frac{1}{\infty} \Rightarrow f = 32 \,cm$.When the tank is filled with water up to a height $h = 20 \,cm$, the light rays are refracted at the water surface.The mirror would have formed an image at $32 \,cm$ from the bottom. Since the water level is at $20 \,cm$, the distance of this image from the water surface is $BO = 32 \,cm - 20 \,cm = 12 \,cm$.This image acts as a virtual object for the water surface. Due to refraction, the apparent height $BI$ from the water surface is given by:$BI = \frac{BO}{\mu} = \frac{12}{4/3} = 12 	imes \frac{3}{4} = 9 \,cm$.Thus, the sunlight focuses at $9 \,cm$ above the water level.

An empty tank has a concave mirror at its bottom. When sunlight falls normally on the mirror, it is focused at a height of $32 \,cm$ from the mirror. If the tank is filled with water up to a height of $20 \,cm$, then the sunlight focuses at (refractive index of water $= 4/3$):

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