When light of wavelength 5000 Å in vacuum travels through same thickness in glass and water, the difference in the number of waves is 400. Find thickness. (Refractive indices of glass and water are `(3)/(2)` and `(4)/(3)` respectively)

Explanation

Difference in number of waves = `l/lamda(mu_(g)-mu_(w))`
`400=l/(5000xx10^(-10))[3/2-4/3]`
`l=400xx5xx6xx10^(-7)`
= `1.2xx10^(-3)m`
= 1.2 mm