The amount of work done in increasing the size of a soap film 10 cm x 6 cm to 10 cm x 10 cm is (surface tension T = 0·030 Nim) :

Options

A. `2.4xx10^(-2)J`
B. `2.4xx10^(-4)J`
C. `4.2xx10^(-2)J`
D. `4.2xx10^(-4)J`

Answer

B

Explanation

Work done = Surface tension `xx` Increase in area
Since soap bubble has two free surfaces.
`therefore` Increase in area= `2 [10 xx 10- 10 xx 6] = 80 cm^(2)`
`therefore` Work done= `0·030 xx 80 xx 10^(-4) = 2·4 xx 10^(-4) J`.
Thus the correct choice is (b).