1.

A thin equiconvex lens is made of glass of refractive index 1.5 and its focal length is 0.2 m, if it acts as a concave lens of 0.5 m focal length when dipped in a liquid, the refractive index of the liquid is :

Answer»

`(17)/(8)`
`(15)/(8)`
`(13)/(8)`
`(9)/(8)`

Solution :(b) `(f_(1))/(f_(a))=(.^(a)mu_(G)-1)/(.^(1)mu_(g)-1)rArr(-0.5)/(0.2)=(1.5-1)/(.^(1)mu_(g)-1)rArr.^(1)mu_(g)-1=-0.2`
`rArr.^(1)mu_(g)=0.8=(4)/(5)rArr(.^(a)mu_(1))/(.^(a)mu_(1))=(4)/(5)rArr(1.5)/(.^(a)mu_(1))=(4)/(5)`
`rArr"" .^(a)mu_(1)=(15)/(8).`


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