# Calculate Charge from Electric Field Diagram?

• P1nkButt3rflys
In summary, the electric field lines around three charges are proportional to the net charge of the charges.
P1nkButt3rflys

## Homework Statement

The diagram shows the electric field lines surrounding three electric charges. Assume that q1 + q2 = -2.43 µC.

A) Calculate q2.

B) Calculate q1.

C) Calculate q3.

## Homework Equations

|Fe|= (k*|q1|*|q2|)/r^2
|E|=(k*|Q|)/r^2

k = 8.99*10^9 (N*m^2)/C^2
Fe = Electrostatic force between a pair of charges
r = charge separation
q1, q2 = charge magnitudes
E = electric field
Q = charged object

## The Attempt at a Solution

I am having a very hard time with this question. I'm not sure where to start. Based on the diagram I assume that q1 and q3 will be equal in charge and magnitude but am not sure where to go from here.

Any help would be greatly appreciated!

Have you learned Gauss's Law/Maxwell's first equation yet? This problem is essentially that. It involves the fact that electric field lines begin on positive charges, and end on negative charges. So the number of electric field lines around a certain charge distribution is proportional to the net amount of charge in that distribution. If you look at the diagram, you have twice as many field lines entering $q_{2}$ as you have leaving $q_{1}$ and $q_{3}$. Using that, what can you determine about the signs and magnitudes of the charges?

Hi again jackarms!

No we haven't learned those concepts yet, we got this assignment about 1 week early and I was trying to be keen. I'm going to read ahead and see if I can figure this out.

Thank you!

Not sure if you got this yet, but the key thing is to look at the direction of the fields. If they travel away, the charge is positive, where as if they travel to, the charge is negative. The amount of field lines entering a charge are proportional to the charge when comparing two charges. So basically, -2Q1 = Q2, as Q1 is positive, but Q2 is negative. Does this make sense?

## 1. How do I calculate the charge from an electric field diagram?

To calculate the charge from an electric field diagram, you will need to use the formula Q = E * A, where Q is the charge, E is the electric field strength, and A is the area of the diagram. Simply multiply the electric field strength by the area to determine the charge.

## 2. What units are used to measure electric field strength?

Electric field strength is typically measured in volts per meter (V/m) or newtons per coulomb (N/C).

## 3. Can I assume that the electric field is uniform in the entire diagram?

In most cases, electric field diagrams represent a uniform electric field, but it is important to check the diagram for any variations or irregularities. If the diagram does not specify a uniform electric field, you may need to use a different formula to calculate the charge.

## 4. What if the electric field diagram has multiple charges?

If the electric field diagram has multiple charges, you will need to calculate the charge for each individual charge and then add them together to determine the total charge.

## 5. Is there a difference between positive and negative charges in an electric field diagram?

Yes, there is a difference between positive and negative charges in an electric field diagram. Positive charges will have electric field lines pointing away from them, while negative charges will have electric field lines pointing towards them. This information can be useful in determining the direction of the electric field and the resulting charge calculation.

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