A tank is filled with water to a height of 15 cm. If the refractive index of water is 1.33, the apparent depth of a needle lying at the bottom of the tank will be
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \( 11.28\,\mathrm{cm} \)
Light from the needle bends away from the normal as it leaves the water, so seen from above (near-normal viewing) the needle appears raised. The apparent depth is the real depth divided by the refractive index.
\( \displaystyle \text{apparent depth} = \frac{\text{real depth}}{n} \)
\( \displaystyle \text{apparent depth} = \frac{15\,\mathrm{cm}}{1.33} \approx 11.28\,\mathrm{cm} \)