An annular disc of radius `r_(1 )= 10 cm` and `r_(2) = 5 cm` is placed on a water surface. Find the surface tension force on the disc if we want to pull it from water surface. Take coefficient of surface tension as `sigma= 7 xx10^(-3) N//m, g = 10 ms^(-12)`.

Answer

`6782.4 dyne`

Explanation

`F=2pir_(1)T+2pir_(2)T`

`=2pi(r_1)1+r_(2))T`
`=2xx3.14(10+5)(72)=6782.4"dyne"`