# Homework Help: Electrial potential problems

1. Jan 4, 2004

### mustang

Problem 10.
Given: k_e=8.98755*10^9 nm^2/C^2 and g=9.8 m/s^2.
Three charges are at three corners of a rectangle a charge of +8.6uC is at the upper left hand corner, a +2.5uC is at the lower left hand corner, and a +3.7 uC is ath the lower right hand corner. The length of the rectangle is 5.1 cm and the width is 3.1 cm.
How much electrical potential energy would be expended in moving the 8.6 uC charge to infinity? Answer in units of J.

Problem 11.
Given: k_e=8.98755*10^9 nm^2/C^2 and g=9.8 m/s^2.
Three charges are located at the vertices of an isosceles triangle. A postive charge is
a the top vertice, and two negative charges are at the bases. The length of the base is 2.7 cm and the other two sides is 5.4 cm.
Calculate the electric potential at the midpoint of the base if the magnitude of each charge is 3.9*10^-9C. Answer in units of V.
note: What formula would you use?

Problem 18.
A parallel-plate capacitor has a capacitance of 0.25 uF and is to be operated at 6300 V.
What is the electrial potential energy stored in the capacitory at the operating potential difference? Answer in units of J.
Note: I don't know where to start.

2. Jan 5, 2004

### himanshu121

Calculate the potential(V) at the point where a charge of 8.6uC is located due to the other two charges. At infinity the potential due to other charges will be zero

Therefore Electric Potential Energy is = q(V-0)

2) Potential at a point due to charge q is kq/r where r is the distance b/w the charge and the point where potential is to be calculated

3) apply the formula 1/2 CV^2