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InterviewSolution
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A transparent thin film of uniform thickness and refractive index `n_(1)``=1.4` is coated on the convex spherical surface of radius R at one end of a long solid glass cylinder of refractive index `n_(2)``=1.5`, as shown in the figure. Rays of light parallel to the axis of the cylinder traversing through the film from air to glass get focused at distance `f_(1)` from the film, while rays of light traversing from glass to air get focused at distance `f_(2)` from the film, Then ` A. `|f_(1)|=3R`B. `|f_(1)|=2.8R`C. `|f_(2)|=2R`D. `|f_(2)|=1.4R |
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Answer» Correct Answer - C `(1)/(f_(film))=(n_(1)-1)((1)/(R)-(1)/(R)) rArr f_(film)=infty` (inf inite) `therefor` No effect of presence of film. For Air to glass Using single spherical Refraction :- `(n_(2))/(v)-(1)/(u)=(n_(2)-1)/(R)` `(1.5)/(v)-(1)/(infty)=(1.5-1)/(R) rArr v=3R` `therefore f_(1)=3R` For Glass to Air `( :-)/` `(1)/(v)-(n_(2))(u)=(1-n_(2))/(-R)` `rArr (1)/(v)-(1.5)/(infty)=(1-1.5)/(-R)` `rArr v=2R` `therefore f_(2)=2R` |
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