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White light is incident on a glass plate of thickness \mathrm{5000 \, \AA} and refractive index 1.5 . The wavelength in the visible region \mathrm{(4000 \, \AA-7000 \, \AA)} that is strongly reflected by the plate is:

Option: 1

\mathrm{4290 \, \AA}


Option: 2

\mathrm{8000 \AA}


Option: 3

\mathrm{4000 \, \AA}


Option: 4

\mathrm{5000 \, \AA}


Answers (1)

best_answer

Light of wavelength \lambda is strongly reflected if

\mathrm{ 2 \mu \mathrm{t}=(2 \mathrm{n}+1) \frac{\lambda}{2} }                         \mathrm{(i)}
If \mathrm{\lambda=4000 \AA, \mathrm{n}=3.25}

If  \mathrm{\lambda=7000 \AA, \mathrm{n}=1.66}

Hence, within \mathrm{4000 \AA}  and \mathrm{7000 \AA} the integer can take values 2 and 3 .                        (from eq. (i))

Putting \mathrm{\mathrm{n}=3,} we get

\mathrm{ \lambda=4290 \AA }

Hence option is \mathrm{\lambda=4290 \AA}

Posted by

Rishabh

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