Question

In above shown figure, a piece of glass is kept in the water and a beam of white is passing through water and glass system. The dashed lines are perpendicular to the surfaces of the glass. Choose the correct statement which describes the changes in the speed and frequency of the light as it passes through the glass.

• A. Both the frequency and speed of the light increase in the glass.
• B. Both the frequency and speed of the light decrease in the glass.
• C. The frequency increases but the speed of the light decreases in the glass.
• D. The frequency decreases but the speed of the light stays constant in the glass.
• E. The frequency stays constant but the speed of the light decreases in the glass.

Answer 1

The correct option is E The frequency stays constant but the speed of the light decreases in the glass.

When light goes from water to glass ,

from fig. $i>r$ ,

By using snell's law $\frac{{\mu }_g}{{\mu }_w}=\frac{\sin i}{\sin r}$

so ${\mu }_g>{\mu }_w$

Now , it is clear that glass is a denser medium than water therefore speed of light will be smaller in it i.e. speed decreases

When light goes from glass to water ,

From fig. $i<r$ ,

By using snell's law $\frac{{\mu }_w}{{\mu }_g}=\frac{\sin i}{\sin r}$

so ${\mu }_g>{\mu }_w$

Now , it is clear that glass is a denser medium than water therefore speed of light will be smaller in it i.e. speed decreases

Now as frequency is characterized by source of light so it will remain constant.