a pond of depth 20 cm is half filled with an oil of refractive index 1.4 and the other half is filled with water of refractive index 1.33. Calculate apparent depth of the tank when viewed normally.
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https://www.meritnation.com/ask-answer/question/a-beaker-20cm-high-filled-with-an-oil-of-r-i-1-4-and-the-upp/ray-optics-optical-instrument/7419091