Two ball bearings, one having a radius of 2 mm and a surface charge density equal to `5muC//m^(2)` and another having a radius of 1mm and a surface de
Two ball bearings, one having a radius of 2 mm and a surface charge density equal to `5muC//m^(2)` and another having a radius of 1mm and a surface density of charge equal to `-2muC//m^(2)` are situated inside a closed surface. The T.N.E.I. over the closed surface is
A. `1.262xx10^(-10)C`
B. `1.262xx10^(-8)C`
C. `2.262xx10^(-8)C`
D. `2.262xx10^(-10)C`
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Correct Answer - D
`R_(1)=2mm,sigma_(1)=5muC//m^(2),R_(2)=1mm,sigma_(2)=-2muC//m^(2),`
`T.N.E.I.=?`
For sphere, `sigma=q/(4piR^(2))" "(thereforeq=sigma4piR^(2))`
Now" "T.N.E.I. = `q_(1)+q_(2)`
`=sigma_(1)4piR_(1)^(2)+sigma_(2)4piR_(2)^(2)`
`=4pi[sigma_(1)R_(1)^(2)+sigma_(2)R_(2)^(2)]`
`=4xx3.14[5xx10^(-6)xx4xx10^(-6)xx-2xx10^(-6)xx1xx10^(-6)]`
`=2.262xx10^(-10)C`
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