A rectangular frame of length 20 cm is dipped in a soap solution and then raised, forming a soup film on the frame. The pull required is 2.83 g wt more before the film breaks. Calculate the surface tension of the liquid.

A rectangular frame of length 20 cm is dipped in a soap solution and t

1.	A rectangular frame of length 20 cm is dipped in a soap solution and then raised, forming a soup film on the frame. The pull required is 2.83 g wt more before the film breaks. Calculate the surface tension of the liquid.
Answer» SOLUTION :The additional pull of 2.83 g wt is equal to the force of surface tension, `F= "2.83 g wt= 2.83 "XX "981 dyne"` As the solution touches the frame both on outside and inside along its length, so force the frame due to surface tension is `F=2 xx l xx sigma=2l sigma` `rArr 2.83 xx 981 =2 xx 10 xx sigma` `rArr sigma=(2.83 xx 981)/(20)="138.8 dyne/cm"`