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An annular disc of radius r(1 )= 10 cm a...

An annular disc of radius `r_(1 )= 10 cm` and `r_(2) = 5 cm` is placed on a water surface. Find the surface tension force on the disc if we want to pull it from water surface. Take coefficient of surface tension as `sigma= 7 xx10^(-3) N//m, g = 10 ms^(-2)`.

A

`6782.4` dyne

B

`67.82` dyne

C

`678.24` dyne

D

none of these

Text Solution

Verified by Experts

The correct Answer is:
A
`F=2pir_1T+2pir_2`
`=2pi(r_1+r_2)T`
`=2xx3.14(10+5)(72)=6782.4` dyne
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