8. Green light of wavelength 5460 Å 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 × $10^8$ $ms^−1$) ?

8. Green light of wavelength 5460 ̊ A 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 × $10^8$ $ms^−1$) ?

(a) 3640 Å

(b) 5460 Å

(c) 4861 Å

(d) none of the above

Answer :  (a) 3640 Å

Frequency remains same , depending on the source.

\( c = \nu \lambda \)

\( v = \nu \lambda_{\text{medium}} \)

\( \nu = \frac{c}{\mu} \)

\( \mu = \frac{c}{v} = \frac{\nu \lambda_{\text{air}}}{\nu \lambda_{\text{medium}}} = \frac{\lambda_{\text{air}}}{\lambda_{\text{medium}}} \)

\( \lambda_{\text{medium}} = \frac{\lambda_{\text{air}}}{\mu} \)

\( \lambda_{\text{medium}} = \frac{\lambda_{\text{air}}}{\mu} \)

\( = \frac{5460\,\text{Å}}{1.5} \)

\( = 3640\,\text{Å} \)