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If the critical angle for total internal...

If the critical angle for total internal reflection from a medium to vacuum is `30^@`, then velocity of light in the medium is .......... `ms^(-1)`. (c = 3.8 `xx 10^8` m`s^(-1)`)

A

`3.0xx10^8`

B

`2.0 xx 10^8`

C

`1.5 xx 10^8`

D

`10^(-8)`

Text Solution

Verified by Experts

The correct Answer is:
A, C
If c is critical angle then
`n=(1)/(sinC)impliessinC=1/n`…........(1)
but `n=c/v` (where v is the velocity in medium)
`therefore 1/n=v/C` …........(2)
From equation (1) and (2),
`sinC=v/C`
`thereforev=sinCxxc`
`(c=3xx10^8,` critical angle C=`30^@`)
`=sin(30^@)xx3xx10^8=1.5xx10^8" "m//s`
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