# Calculating net force on a charge placed at a spot

• phys62
In summary, the problem involves two fixed charges, -16 and +3.4 mC, separated by 4.4 m. The first part asks for the location where the net electric field is zero, which is found to be 3.76 m away from the positive charge. In the second part, a charge of +14 mC is placed at this spot, but it does not experience a force due to the zero electric field at that location. The force is calculated using the equation F=qE, but because E = 0, the resulting force is also 0.
phys62

## Homework Statement

Two charges, -16 and +3.4 mC, are fixed in place and separated by 4.4 m. (a) At what spot along a line through the charges is the net electric field zero? Give the distance of the spot to the positive charge in meters (m). (Hint: The spot does not necessarily lie between the two charges.) (b) What would be the force on a charge of +14 mC placed at this spot?

E=kq/r^2

## The Attempt at a Solution

I've figured out part a, but I don't know what I'm doing wrong on part b... here is my work:

a) the correct answer is 3.76 m.

b) F21=(8.99x10^9)(3.4x10-6)(14x10-6)/(3.76 m)^2 = 0.03026 N
F23=(8.99x10^9)(-16x10^-6)(14x10-6)/(4.4+3.76)^2 = -0.0302 N

then I added the 2 together and got 1.68x10^-5 N
Am I supposed to actually get 0 as my answer? I'm so confused.

F=qE. Because E = 0 at this spot any charge placed at this spot will not experience a force. It's analogous to zero gravity; any mass placed in a zero gravity field will not experience a force.

I can confirm that your calculations for part a are correct. The net electric field at a distance of 3.76 m from the positive charge is zero, as the repulsive force from the positive charge is balanced by the attractive force from the negative charge.

For part b, you are correct in using the equation F=ke(q1q2)/r^2 to calculate the force between the two charges. However, you should first calculate the distance between the charge of +14 mC and the two fixed charges (-16 mC and +3.4 mC) at the spot where the net electric field is zero. This distance will be different from the 3.76 m you calculated in part a.

Once you have the correct distance, you can plug it into the equation to calculate the force on the +14 mC charge. The resulting force should be zero, as the net electric field at this spot is zero and there is no force acting on the charge.

## 1. What is net force on a charge?

Net force on a charge is the overall force acting on a charged particle, taking into account all the individual forces acting on it.

## 2. How do you calculate net force on a charge?

To calculate net force on a charge, you need to add up all the individual forces acting on the charge. These forces can be electric, magnetic, or gravitational in nature.

## 3. What factors affect the net force on a charge?

The net force on a charge is affected by the strength and direction of the individual forces acting on it, as well as the charge of the particle itself.

## 4. Can the net force on a charge be zero?

Yes, the net force on a charge can be zero if the individual forces acting on the charge are equal in magnitude but opposite in direction.

## 5. How does the distance between charges affect the net force on a charge?

The distance between charges affects the net force on a charge through the inverse square law, which states that the force between two charges is inversely proportional to the square of the distance between them. As the distance increases, the net force on the charge decreases.

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