A light of wavelength 4 x 10−7 m from air is incident on a glass slab of refractive index 1.5. The wavelength of the refracted light will be
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 2.66 x 10−7 m
When light enters another medium its frequency stays the same, while its speed, and hence its wavelength, is reduced by the factor \( \mu \).
\( \displaystyle \lambda_{\mathrm{glass}} = \frac{\lambda_{\mathrm{air}}}{\mu} \)
\( \displaystyle \lambda_{\mathrm{glass}} = \frac{4\times10^{-7}}{1.5} \)
\( \displaystyle \lambda_{\mathrm{glass}} \approx 2.67\times10^{-7}\,\mathrm{m} \)
This is the value in Option (1), which gives it as 2.66 × 10−7 m.
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
