Question 11:
easyA beam of monochromatic light is refracted from vacuum into a medium of refractive index 1.5. The wavelength of refracted light will be
(1992, 91)
When light travels from a rarer medium like vacuum to a denser medium, its frequency remains unchanged while its velocity decreases. Since velocity $v = f \lambda$, the wavelength also decreases. Specifically, $\lambda' = \frac{\lambda}{\mu}$, making the new wavelength smaller.
Question 12:
easyGreen light wavelength 5460 $\AA$ is incident on an air-glass interface. If the refractive index of glass is 1.5, the wavelength of light in glass would be ($c = 3 \times 10^8 ms^{-1}$)
(1991)
The wavelength of light in a medium is given by $\lambda' = \frac{\lambda}{\mu}$. Substituting the given values, the wavelength in glass is $\lambda' = \frac{5460 \AA}{1.5} = 3640 \AA$.
Question 13:
easyA star, which is emitting radiation at a wavelength of 5000 $\AA$, is approaching the earth with a velocity of $1.5 \times 10^4 m/s$. The change in wavelength of the radiation as received on the earth is:
(1995)
For a star approaching the earth at a speed much less than $c$, the change in wavelength (Doppler shift) is $\Delta\lambda = \lambda \frac{v}{c}$. Substituting the values, $\Delta\lambda = 5000 \times \frac{1.5 \times 10^4}{3 \times 10^8} = 5000 \times 0.5 \times 10^{-4} = 25 \AA$.