The apparent thickness of a thick plano-convex lens is measured once with the plane face upward and then with the convex face upward. The value will be

Options

A. more in the firest case
B. same in the two cases
C. more in the second case
D. any of the above depending on the value of its actual thickness

Answer

c.

Explanation

`(mu_(2))/(-mu)+(mu_(1))/(v)=(mu_(1)-mu_(2))/(R)=0`
In the first case,
`(mu)/(-d)+(1)/(-v)=(mu_(1)-mu_(2))/(oo)=0`
or `1/(-v)=mu/d`
or `v=-d/mu`
In the second case,
`mu/(-d)+1/(-v')=(1-mu)/(-R)`
or `(1)/(-v^('))=(mu)/(-d)-(1-mu)/(-R)`
or `(1)/(-v^('))=(1)/(-v)+(1-mu)/(-R)`
Clearly, `(1)/(-v^(')) gt (1)/(-v)`
or `(1)/(-v^(')) lt (1)/(-v)`
or `v^(') gt v`