A point charge with q1=+2.40 micro-coulombs is helf stationary at the origin. A

Question

A point charge with q1=+2.40 micro-coulombs is helf stationary at the origin. A second point charge q2=-4.30micro-coulombs moves from point a(x=0.150m, y=0) to point b(x=0.250m, y=0.250m).

a. What is the electric potential energy of the system when q1 is at the origin and q2 is in the original position?

b. What is the electric potential energy of the system when q1 is at the origin and q2 is in the final position?

c. How much work is done by the electric force on q2 to move it from the original position to the final position?

Explanation / Answer

a) Disance between the charges = r = 0.15

E = k Q1 Q2 / r

= 9 * 10^9 * 2.4*10^(-6) * (-4.3 * 10^(-6)) / 0.15

= -0.6192 J

b)

Disance between the charges = r = 0.25 * sqrt (2) = 0.3536

E = k Q1 Q2 / r

= 9 * 10^9 * 2.4*10^(-6) * (-4.3 * 10^(-6)) / 0.3536

= -0.262 J

c) Work done by external force

= change in energy

= E2 - E1

= (- 0.262) - (- 0.6192)

= 0.3572 J

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