Question

"A light wave passes from air into water. Which of the following is true? 1. Its frequency remains unchanged, but its wavelength decreases. 2. Its wavelength remains unchanged, but its frequency decreases. 3. Its wavelength remains unchanged, but its frequency increases. 4. None of these 5. Both its wavelength and its frequency remain unchanged."

Answer 1

Answer:

1. Its frequency remains unchanged, but its wavelength decreases.

Explanation:

When the light wave passes from air to water then the speed of light wave reduces due to water being optically denser than the air.

According to the conservation of energy the energy of the photons before and after the refraction remains same and as the energy of the wave is dependent on the frequency so the frequency of the wave does not changes.

We know the relation between the frequency, speed and the wavelength of the light as:

$\nu=\frac{v}{\lambda}$

where:

$\nu=$ frequency of the wave

$v=$ speed of light in the medium

$\lambda=$ wavelength of the wave

Now from the above relation we can observe that if frequency has to remain constant while the speed of the wavelength reduces in and optically denser medium then the wavelength must also reduce proportionally.

$v=\lambda.\nu$

$v\propto\lambda$

Answer 2

Answer:

option (1)

Explanation:

Frequency is the fundamental property of the source of light. The number of vibrations coming out from the source in one second is called frequency.

So, the frequency of light is constant as the light passes from air to water.

The velocity of light decreases as the light passes from air to water.

So by the formula

v = f x λ

As frequency remains same and velocity decreases so that the wavelength also decreases.

Option (1)