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White light is incident normally on a gl...

White light is incident normally on a glass plate (in air) of thickness `500 nm` and refractive index of `1.5`. The wavelength (in `nm`) in the visible region `(400 nm-700nm)` that is strongly reflected by the plate is:

A

4500 Å

B

6000 Å

C

4000 Å

D

4000 Å

Text Solution

Verified by Experts

The correct Answer is:
B
Light of wavelength `lamda` is strongly reflected if
`2mut=(2n+1)lamda//2` . . (i)
If `lamda=4000` Å
solving it for n we get n=3.25
Similarly for `lamda=7000Å` we get n=1.66
Hence, within 4000 Å and 7000 Å, integer can take value 2 and 3, from equation (i)
`lamda=4mut//(2n+1)`
Substituting n=2 and n=3, we get =6000Å and 4286 Å.
So these two wavelengths are reflected strongly.
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