1.

Focal length of convex lens having refractive index 1.5 is 2 cm. If this lens is dipped in a liquid having refractive index 1.25 its focal length will be ...... cm.

Answer»

10
2.5
5
7.5

Solution :`(f_a)/(f_l)=((n_g)/(n_l)-1)/((n_g)/(n_a)-1)=(n_g-n_l)/(n_g-n_a)XX(n_a)/(n_l)`
`(2)/(f_1)=(1.5-1.25)/(1.5-1.00)xx(1.00)/(1.25)`
`thereforef_l=(2xx1.25xx0.5)/(1.0xx0.25)`
`thereforef_l=(1.25)/(0.25)thereforef_l=5` CM


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