A light wire AB of length 10 cm can slide on a vertical frame as shown in figure. There is a film of soap solution trapped between the frame and the wire. Find the load W that should be suspended from the wire to keep it in equilibrium. Neglect friction. Surface tension of soat solution `=25` dyne `cm^-1`. Take `g=10 ms^-2`

Explanation

Soap solutioin film will be formed on both sides of the frame. Each film is in contact with the wire along a distanc eo 10 cm The force exerted by the film on the wire
`=2xx(10cm)xx(25dyne cm^-1)`
`=500dyne=5xx10^-3N`.
This force acts vertically upward and should be balanced by the load. Hence the load that should be suspended is `5xx10^-3N`. The mass of the load should be
`(5xx106-3N)/(10ms^-2)=5xx10^-4kg=0.54g`.