Question

Consider a light wave that passes from air into a very thick clear glass block that has its opposite internal side mirrored (facing into the glass). The light ray passes into the glass block at an angle greater than $0^{\circ }$ and less than ${90}^{\circ }$, strikes the mirrored surface and reflects back through the glass into the air.
What happens while the light ray is in the glass block but before it strikes the mirrored surface?

• A. The frequency of the waves increases
• B. The frequency of the waves decreases
• C. The wavelength of the waves decreases
• D. The velocity of the waves decreases
• E. The period of the waves increases

Answer 1

Answer: (C), (D)

The wavelength of the waves decreases
The velocity of the waves decreases

When a light ray enters in a medium of higher refractive index from a lower one, the speed of the wave decreases as $v=\frac{c}{\mu }$

Since $\lambda =\frac{v}{\nu }$ and the frequency remains unchanged,

$\lambda =\frac{{\lambda }_0}{\mu }$

Hence the wavelength and the velocity of the waves decreases.