# Two Charges - Electric Potential Question

by pierretong
Tags: charges, electric, potential
 P: 3 1. The problem statement, all variables and given/known data Two charges q = 4.0μ C are fixed in space a distance d = 4.0 cm apart, as shown in the figure. With V = 0 at infinity, what is the electric potential at point C? You bring a third charge q = 4.0μC from infinity to C. How much work must you do? What is the potential energy U of the three-charge configuration when the third charge is in place? Diagram shows (let me use x-y coordinate terms to describe this). Charge q at the origin. Another charge q at (4 cm, 0 cm) and point C at (2 cm, 2 cm) 2. Relevant equations Electric Potential = kQ/r 3. The attempt at a solution That's the right equation for the first part correct? I get 1.27*10^4 for the electric potential for one of the charges on point C. When you double that, you get 2.5 * 10^4 V and that should be the answer? (online homework system says that it is wrong). What am I doing wrong here? Also I don't understand the second part. If you are moving a charge from infinity, how can you calculate the work? You don't know the distance?
Emeritus
HW Helper
PF Gold
P: 7,819
 Quote by pierretong 1. The problem statement, all variables and given/known data Two charges q = 4.0μ C are fixed in space a distance d = 4.0 cm apart, as shown in the figure. With V = 0 at infinity, what is the electric potential at point C? You bring a third charge q = 4.0μC from infinity to C. How much work must you do? What is the potential energy U of the three-charge configuration when the third charge is in place? Diagram shows (let me use x-y coordinate terms to describe this). Charge q at the origin. Another charge q at (4 cm, 0 cm) and point C at (2 cm, 2 cm) 2. Relevant equations Electric Potential = kQ/r 3. The attempt at a solution That's the right equation for the first part correct? I get 1.27*10^4 for the electric potential for one of the charges on point C. When you double that, you get 2.5 * 10^4 V and that should be the answer? (online homework system says that it is wrong). What am I doing wrong here? Also I don't understand the second part. If you are moving a charge from infinity, how can you calculate the work? You don't know the distance?
Hello pierretong. Welcome to PF !