1.

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) :

Answer»

`2.4xx10^(-2)J`
`2.4xx10^(-4)J`
`4.2xx10^(-2)J`
`4.2xx10^(-4)J`

Solution :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).


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