A metal ring of internal and external radii 15 mm and 20 mm respectively is placed horizontally on the surface of a liquid of surface tension 0.03 N/m To detach the ring from the liquid surface the force required is

Options

A. `28 xx 10^(-5)`N
B. `66xx10^(-4)`N
C. `6.6 xx10^(-4)`N
D. `425 xx 10^(-4)`N

Answer

B

Explanation

`2pi (r+R)T = =F`
` F = 2pi (15xx 10^(-3) + 20 xx 10^(-3))xx3 xx 10^(-2)`
` 2pi (35) xx 10^(-3) xx 3xx 10^(-2)`
` = 659.7 xx10^(-5)`
` = 66 xx 10^(-4)` N