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 .

Explanation

`q_(1)= 10muC= 10xx10^(-6)C`
`q_(2) =- 2 muC = -2 xx10^(-6)C `
distance ,`r = 5cm = 5xx10^(-2)` m
Change in potential energy `DeltaU = (9xx10^(9) xx10^(2)xx10^(6)xx(-2xx10^(-6)))/(5xx10^(-2)) `
`=-36xx10^(9)xx10^(-12)xx10^(2)= -36xx10^(-1)`
`DeltaU = 3.6 J`
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 <
`DeltaU=-3.6 J` negtive sign implies that to move the charge `-2muC` no external work is required system spend its stored energy to move the charge from poitnt a to point b.