Question

A rectangular film of liquid is formed in the a frame of wire and a movable rod of length 4cm. What
force must be applied to the rod to keep it in equilibrium if the surface tension of liquid is 40x 10 N/m?​

Answer 1

Answer:

Given: Length of the rod = l = 4 cm = 4 × 10-2 m, Surface tension = T = 40 × 10-3 N/m

To Find: Force required = F =?

Solution:

In case of rod, the liquid wets it from two sides,

Hence, the effective length = 2 l = 2 × 4 × 10-2 m

We have, T = F / effective length

∴ F = T × effective length = 40 × 10-3 × 2 × 4 × 10-2 = 3.2 × 10-3 N

Ans: Force required is 3.2 × 10-3 N

Answer 2

Answer:

32N

Explanation:

F=T.(effective length)

T=40×10N/M

L=4cm=0.04m

L(effective length)=2×0.04

                              =0.08

F=400N/m×0.08

            =32N