A thin liquid film formed between a `U-`shaped wire and a light slider supports a weight of `1.5 xx 10^(-2)N`(see figure). The length of the slider is `30 cm` and its weight negligible. The surfaces tension of the liquid film is :

Options

A. `0.0125 N m^(-1)`
B. `0.1 N m^(-1)`
C. `0.05 N m^(-1)`
D. `0.025 N m^(-1)`

Answer

D

Explanation

Here, `W= 1.5xx10^(-2) N, l=30 cm =30 xx 10^(-2)m`
The force due to surface tension will the balance the weight. i.e., F=W
A liquid film has two free surfaces.
2TL=W or `T=(W)/(2L)`
`T=(1.5xx10^(-2))/(2xx30xx10^(-2))=0.025 N m^(-1)`

A slider will suport the weight when the force of surface tension acting upwards on the slider `(=2Sl)` balances the downward force due to weight (=W)