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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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Charges `q_1 = 10 xx 10^-6C`
`q_2 = -2 xx 10^-6C`
Distance of separation r = 5 cm = `5 xx 10^-2` m change in potnetial energy of the system.
`DeltaU = 1/(4piepsilon_0)(q_1 xxq_2)/r`
`= (9 xx 10^9 xx (10 xx 10^-6)(-2 xx 10^-6))/(5 xx 10^-2)`
`= (9 xx 10 xx (-2) xx 10^-3)/(5 xx 10^-2)`
`= -36 xx 10^-1 = -3.6J`
`:.DeltaU = -3.6J(-3.246J)`
From the negative sign, it is implied that no exteral work is required to move the charge `-2muC`. System spends its stored energy to move the charge from point a to point b.
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