Question

Why does the coin placed in water appear raised?

Hint:

Formula for apparent depth: $ \text{Apparent depth} = \frac{\text{Real depth}}{\text{Refractive index}} $.

Answer 1

Step 1: Refraction of Light
When light passes from one medium to another (for example, from water to air), its speed changes because the optical density of the medium changes. This bending of light rays at the interface is called refraction.
Step 2: Coin Example
A coin placed at the bottom of a glass of water sends light rays upwards. As these rays pass from water (denser medium) to air (rarer medium), they bend away from the normal.
Step 3: Virtual Image Formation
The refracted rays do not come from the actual position of the coin but appear to be coming from a point slightly above it. To the observer’s eye, the coin seems to be raised. This shifted position is called a virtual image.
Step 4: Scientific Explanation
The apparent depth of the coin is less than the real depth because of refraction. This is why swimming pools look shallower than they really are.
Step 5: Real-Life Applications
This principle is used in designing lenses and optical instruments.
Fishermen often notice that fish inside water do not appear at their actual position; they appear raised. That is why aiming directly at the fish misses the target.
Final Answer:
The coin appears raised due to the refraction of light at the boundary of water and air, which shifts its apparent position upward.