Question

The wave number of a beam of light in air is ` 2.5 xx 10^(6)` per metre. What is its wavelength in glass of refractive index 1.6 ?
A. `2000 Å `
B. `2500Å`
C. `2750Å`
D. `3000Å`

Answer 1

Correct Answer - B
`lambda_("air")=(1)/("wave number in air ")`
`=(1)/(2.5 xx 10^(6))=4 xx 10^(-7)m =4000 Å`
By definition , `""_(a)n_g=(v_("air"))/(v"glass")=(lambda"air")/(lambda_("glass"))`
`:. lambda_(g)=(lambda_("air"))/(""_(a)n_g)=(4000)/(1.6)=2500Å`