Question

When a 'U' shaped slider of negligible mass is dipped in a soap solution and lifted, a thin film of soap is formed in the frame. It supports a weight of 2.0 x 10${}^{-2}$ N. If the length of the slider is 40cm, the surface tension of the film of soap is:

• A. 25 Nm${}^{-1}$
• B. 2.5 Nm${}^{-1}$
• C. 2.5 x 10${}^{-2}$ Nm${}^{-1}$
• D. 2.5 x 10${}^{-3}$ Nm${}^{-1}$

Answer 1

The correct option is C 2.5 x 10${}^{-2}$ Nm${}^{-1}$

Given:
Length of the slider $=40$ cm

Weight supports $=2.0\times {10}^{-2}$ N

The surface tension here is given as $\sigma =\frac{F}{2l}=\frac{2\times {10}^{-2}}{2\times 0.4}=2.5\times {10}^{-2}N{m}^{-1}$