Question

When trying to catch a fish, should a pelican dive into the water horizontally in front of or behind the image of the fish it sees?
A. In front of image
B. Behind the image
C. Cannot be inferred
D. None

Answer 1

Hint: Velocity of light will be different in different media. If velocity of light is higher in one medium and lesser in another medium then the first one is called a rarer medium and the second one is called a denser medium. The path travelled by light also varies with its velocity.

Complete step by step answer:
Velocity is nothing but the rate of change of displacement i.e the ratio of displacement to the time taken. So the time taken will be displacement upon the velocity.
Velocity of light in any medium of refractive index(n) will be
$v = \dfrac{c}{n}$ where ‘c’ is the velocity of light in the free space and ‘n’ is the refractive index of the medium.

For air, the refractive index will be one. The water refractive index will be greater than one. Hence when light enters from water to air, its velocity increases. In order to maintain the same time displacement also must increase. That means the path travelled in the air by the light must increase. This will be possible if the light bends away from the normal. This is clearly shown in the diagram below.

The image of the fish appears nearer to the pelican than at the actual place. So the pelican should dive in front of the image to catch the fish.

Hence option A will be the correct answer.

Note:
If the fish is seeing the pelican from the water, then the opposite happens. Pelican appears at a longer distance than the actual distance. For pelican fish appears nearer so when the pelican tries to catch the image of the fish, the actual fish becomes alert and escapes from the pelican.