Question

A soap film is trapped between a frame and a wire of length $10cm$ as shown in figure. If the surface tension is given as $0.0049N/m$, what will be the value of mass $\left(m\right)$ such that the wire remains in equilibrium?

• A. 0.1 mg
• B. 1 mg
• C. 10 mg
• D. 100 mg

Answer 1

The correct option is D 100 mg

For the wire to be in equilibrium, forces exerted by the film on the wire due to surface tension (acting upwards) must be equal to downward force due to weight of the wire (acting downwards).
$\sigma$ - surface tension
l - length of wire
$mg=2\sigma l$
$m=\frac{2\sigma l}{g}$
$m$ $=$ $100$ mg