A planoconvex lens has a maximum thickness of 6 cm. When placed On a horizontal table with the curved surface in contact with the table surface, the apparent depth of the bottommost point of the lens is found to be 4 cm. If the lens is inverted such that the plane face of the lens is in contact with the surface of the table, the apparent depth of the center of the plane face is found to be `(17/4)cm`. The radius of curvature of the lens is.............

Options

A. 68 cm
B. 75cm
C. 128 cm
D. 34 cm

Answer

D

Explanation

In case of refraction from a curved surface.

Here,`mu_(1)=mu,mu_(2)=1`
u=-6cm,v=-4 cm,`R=oo`
`therfore (1)/((-4))-(mu)/((-6))=(1-mu)/(00)`
or `mu=(6)/(4)=(3)/(2)`
And when plane surface is on the table,refraction will take place at curved surface

Here `mu_(1)=mu=(3)/(2),mu_(2)=1`
u=-6cm,v`=-(17)/(4)` cm
`(1)/((-17//4))-((3//2))/((-6))=(1-(3//2))/((-R))`
`(-4)/(17)+(1)/(4)=(1)/(2R)implies(-16+17)/(68)=(1)/(2R)`
`implies(1)/(68)=(1)/(2R)impliesR=(68)/(2)`cm=34cm