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A point charge of +10 mu C is placed at ...

A point charge of +10 `mu` C is placed at a distance of 20 cm from another identical point charge of +10 `muC`. A point charge of `-2mu` C is moved from point a to b as shown in the figure . Calculate the change in potential energy of the system ? Interpret your result .

Text Solution

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The correct Answer is:
Given : `q_(1)=10xx10^(-6)C,q_(2)=-2xx10^(-6)C`
r=5xx10^(-2)m`
Change in potential energy
`DeltaU=(1)/(4piepsi_(0))(q_(1)q_(2))/(r)=(9xx10^(9)xx(10)(-2)xx10^(-12))/(5xx10^(-2))`
`=(-9xx10^(9)xxoverset(4)cancel(20)xx10^(-12)xx10^(2))/(cancel(5))`
`=-36xx10^(-1)=-3.6J`
`DeltaU=-3.6J` negative sign implies that to move the charge `-2muC` no external work is required. System spends its stored energy to move the charge from point a to point b.
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