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Critical angle of glass-air is 42^@, the...

Critical angle of glass-air is `42^@`, then speed of light in glass is .....

A

`3 xx 10^8` m`s^(-1)`

B

`2 xx 10^8` m`s^(-1)`

C

`1.5 xx 10^8` m`s^(-1)`

D

`2.5 xx 10^8` m`s^(-1)`

Text Solution

Verified by Experts

The correct Answer is:
A, B
Critical angle C=`42^@`
Speed in air c=`3xx10^8 ms^(-1)`
Refractive index n=`c/v` but n=`(1)/(sinC)`
`therefore(1)/(sinC)=(3xx10^8)/(v)`
`therefore v=3xx10^8xxsinC`
`=3xx10^8xxsin42^@` `=3xx10^8xx0.6691`
`=2.0073xx10^8`
`therefore v~~2xx10^8ms^(-1)`
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