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    				| 1. | A film of water is formed between two straight paralel wires each `10 cm` long and at seperation `0.5 cm`. Calculate the work requied to increase `1mm` distance between the wires. Surface tension of water `=72xx10^(-3)N//m`. | 
| Answer» Initial surface area `=2xx"length"xx"separation"` `=2xx10cmxx0.5cm=10cm^(2)=10xx10^(-4)m^(2)` Final surface area `=2xx10cmxx(0.5+0.1)cm` `=2xx10xx0.6cm^(2)=12xx10^(-4)m^(2)` The required work `WT/_A=72xx10^(-3)xx(12xx10^(-4)-10xx10^(-4))J` `=72xx10^(-3)xx2xx10^(-4)=144xx10^(-7)J` | |