PLEASE DO NOT POST ANY OTHER PREVIOUSLY SOLVED PROBLEM WITH DIFFERENT VALUES AS

Question

PLEASE DO NOT POST ANY OTHER PREVIOUSLY SOLVED PROBLEM WITH DIFFERENT VALUES AS A SOLUTION TO THIS QUESTION.

1)

Determine the electric potential energy for the array of three charges in the drawing, relative to its value when the charges are infinitely far away and infinitely far apart. (Let q1 = 7.60 ?C, q2 = 18.6 ?C, and q3 = ?13.9 ?C.)

_______________J

2)

In the drawing below, R1 has a resistance of 8.7 ? and R2 has a resistance of 2.2-?. Determine the current (magnitude and direction) in the 8.7 and 2.2-?resistors in the drawing.

IR1 = ______________ A from left to the right

IR2 = ______________ A from left to the right

IR1 = ______________ A from left to the right

IR2 = ______________ A from left to the right

Explanation / Answer

1)
The electric potential energy stored in a group of point charges, compared to when they are infinitely far apart is the sum of the potential energies of all possible pairs.
So for three point charges it would be;
U = kq1q2/r12 + kq1q3/r13 + kq2q3/r23

In your problem the charges are at the vertices of a 3-4-5 right triangle so;
U = kq1q2/5 + kq1q3/3 + kq2q3/4

So just put in the charge values and add them up.
This eq. is "sign" sensitive, so the last two terms will be negative because q3 is negative.

2)
R2 is 2.2 ohms and has a voltage across it of 12 volts.

I = E/R = 12/2.2 = 5.45 amps.

R1 is 8.7 ohms and has 16 volts across it

I = E/R = 16/8.7 = 1.839 amps.

In both cases conventional current flow is from left to right

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