White light may be considered to be mixture of waves of `lambda` ranging between `3900 Å` and `7800 Å`. An oil film of thickness `10,000 Å` is examined normally by the reflected light. If `mu=1.4`, then the film appears bright for

Options

A. `4000 Å, 4667 Å, 5600 Å, 7000 Å`
B. `4308 Å, 5091 Å, 6222 Å`
C. `4000 Å, 5091 Å, 5600 Å`
D. `4667 Å, 6222 Å, 7000 Å`

Answer

B

Explanation

`2 mut-lambda/2=nlambda`
`2mut=(n+1//2)lambda`
`lambda=(2mut)/(n+1//2)=(2xx1.4xx10000)/(n+1//2)=28000/(n+1//2)`
`n=0, lambda=56000 Å`
`n=1, lambda=15333 Å`
`n=2, lambda=11200 Å`
`n=3, lambda=8000 Å`
`n=4, lambda=6222 Å`
`n=5, lambda=5091 Å`
`n=6, lambda=4308 Å`
` lambda=4308 Å, 5091 Å, 6222 Å`