Question

A circular wire of length 0.1m is touching the surface of the liquid of surface tension
3.5 x 10-N m-'. The mass of a wire is 10^4kg. If g=10m/s^2. The force needed to lift the
circular wire is
1) 7x10^-3N
2) 0.7 x10^-3N 3) 0.07 x 10^-3N
4) 70 x 10^-3N
​

Answer 1

Force needed to lift the  circular wire is 0.7 x  $10^{-5}$ N

Total length =l  = 2 x 0.1 m = 0.2m

F = $F_{T}$ + mg

=T X 2l + 10 x $10^{-4}$

=3.5 x $10^{-2}$ x 0.2 + $10^{-3}$

=0.7 x  $10^{-5}$ N.

∴Force needed to lift the  circular wire is 0.7 x  $10^{-5}$ N