# Solving Electric Magnetism Problems: Forces, Fields, Potentials, Work

• brains
In summary, the conversation discusses the calculation of the force of repulsion and electric field between two charges of 6 and 10 microcoulombs placed 10cm apart, as well as the potential and work required to bring an electron from far away to midway between the charges. The formula for the force and electric field are correctly applied, resulting in a force of 53.94N and an electric field of 3.6 x 10^6 N/c. However, there is some confusion with the calculation of the electric field midway, as well as the use of the formula for potential energy instead of potential. The correct approach is to find the relationship between potential and potential energy, and to take into account half the original distance
brains
I need some help figuring #2 problem out.

Homework Statement

1. two charges of 6 microcoulombs and 10 microcoulombs are 10cm apart. Calculate their force of repulsion. Calculate the electric field midway between them.
2. For the charges in question 1 calculate the potential midway between them. Calculate the work to bring an electron from far away to midway between them.
So for the first question I used F= k |q1||q2|/r^2 for the second part of the first question i did E = k |q|/r^2

i calculated that the force would be 53.94N
As for the electric midway I calculate it to 3.6 x 10^6 N/c Although I am not sure if i was supposed to add or subtract E1 and E2. So what i did is that i subtracted. But I am not entirely sure if that is my correct answer My work:
E1 = 8.99x 10^9 N*m^2/c^2 x |6 x10^-6 C|/(0.1m)^2

E1 = 5.39 x 10^6 N/c is my answer for E1

E2 = 8.99 x 10^9 N*m^2/c^2 x |10 x 10^-6C|/(0.1m)^2

E2 = 8.99 x 10 ^6 N/C

Then i did E = 8.99 x 10^6 N/C - 5.39 X 10^6 N/C
And I got 3.6 x 10^6 N/C however like i said before I am not exactly sure if this was the correct approach to get the electric field midwayFor the second question
I used this equation (U= k (q0)(q)/r ---> k being 8.99 x10^9n.m^2/c^2 for part of the 1st question in question 2 that asks for potential midway and got an answer of U= 10.78 N M

however when they asked me for the work in question two i assumed I should have used -W=q0Ed
but i don't know what numbers I would use for this equation. Would the correct way of going about it be
doing -W=(1.60 x 10^-19C)(8.99 x 10^6 N/C - 5.39 X 10^6 N/C)(0.1m) or is this wrong?

IF someone could please point me in the right direction and check if I've done these steps correctly it would be helpful. Thank you in advance.

Last edited:
brains said:
I need some help figuring #2 problem out.

Homework Statement

1. two charges of 6 microcoulombs and 10 microcoulombs are 10cm apart. Calculate their force of repulsion. Calculate the electric field midway between them.

2. For the charges in question 1 calculate the potential midway between them. Calculate the work to bring an electron from far away to midway between them.

So for the first question I used F= k |q1||q2|/r^2 for the second part of the first question i did E = k |q|/r^2

i calculated that the force would be 53.94N
As for the electric midway I calculate it to 3.6 x 10^6 N/c Although I am not sure if i was supposed to add or subtract E1 and E2. So what i did is that i subtracted. But I am not entirely sure if that is my correct answer

My work:
E1 = 8.99x 10^9 N*m^2/c^2 x |6 x10^-6 C|/(0.1m)^2

E1 = 5.39 x 10^6 N/c is my answer for E1

E2 = 8.99 x 10^9 N*m^2/c^2 x |10 x 10^-6C|/(0.1m)^2

E2 = 8.99 x 10 ^6 N/C

Then i did E = 8.99 x 10^6 N/C - 5.39 X 10^6 N/C
And I got 3.6 x 10^6 N/C however like i said before I am not exactly sure if this was the correct approach to get the electric field midway

For the second question
I used this equation (U= k (q0)(q)/r ---> k being 8.99 x10^9n.m^2/c^2 for part of the 1st question in question 2 that asks for potential midway and got an answer of U= 10.78 N M

however when they asked me for the work in question two i assumed I should have used -W=q0Ed
but i don't know what numbers I would use for this equation. Would the correct way of going about it be
doing -W=(1.60 x 10^-19C)(8.99 x 10^6 N/C - 5.39 X 10^6 N/C)(0.1m) or is this wrong?

IF someone could please point me in the right direction and check if I've done these steps correctly it would be helpful. Thank you in advance.

Hey there!

So for the first question I used F= k |q1||q2|/r^2 for the second part of the first question i did E = k |q|/r^2

i calculated that the force would be 53.94N

Yep. That's right.

As for the electric midway I calculate it to 3.6 x 10^6 N/c Although I am not sure if i was supposed to add or subtract E1 and E2. So what i did is that i subtracted. But I am not entirely sure if that is my correct answer

My work:
E1 = 8.99x 10^9 N*m^2/c^2 x |6 x10^-6 C|/(0.1m)^2

E1 = 5.39 x 10^6 N/c is my answer for E1

E2 = 8.99 x 10^9 N*m^2/c^2 x |10 x 10^-6C|/(0.1m)^2

E2 = 8.99 x 10 ^6 N/C

Then i did E = 8.99 x 10^6 N/C - 5.39 X 10^6 N/C
And I got 3.6 x 10^6 N/C however like i said before I am not exactly sure if this was the correct approach to get the electric field midway

You're almost correct here - I'd say to take a look at your value for r again. As in, what are you measuring r to be again?

As for both parts of the second question:

I used this equation (U= k (q0)(q)/r
...i assumed I should have used -W=q0Ed

The formula for U is for electrical potential energy, not the potential. But - there's a relationship between the two quantities, as well as one between W and U. Once you find those out, you're good to go.

1 person
You're almost correct here - I'd say to take a look at your value for r again. As in, what are you measuring r to be again?

Well I take the idea it's 10cm i converted that into 0.1m. Um I am guessing since they are asking me to calculate the electron from far away to midway. I would only take into account half of the original distance right?

brains said:
You're almost correct here - I'd say to take a look at your value for r again. As in, what are you measuring r to be again?

Well I take the idea it's 10cm i converted that into 0.1m. Um I am guessing since they are asking me to calculate the electron from far away to midway. I would only take into account half of the original distance right?

brains said:
Well I take the idea it's 10cm i converted that into 0.1m. Um I am guessing since they are asking me to calculate the electron from far away to midway. I would only take into account half of the original distance right?

In regards to the Electric field problem, the question asks for the electric field at the midway point between the two charges. A radius of 10 cm here would imply that the point in question is at either charge.

With respect to the Potential Energy, yes. To be more technical, it's ΔU = Uf - U0, and if you use an r = ∞ for Uf, that expression becomes just -U0.

Sorry for the late reply and thank you very much i finally understood it :D.

## What is electric magnetism?

Electric magnetism is a branch of physics that deals with the interaction of electric and magnetic fields. It explains how these fields are created and how they interact with each other and with charged particles.

## What is the difference between electric and magnetic fields?

The main difference between electric and magnetic fields is that electric fields are created by stationary electric charges, while magnetic fields are created by moving electric charges. Electric fields also exert forces on charged particles, while magnetic fields only exert forces on moving charged particles.

## How do I calculate the force between two charged particles?

The force between two charged particles can be calculated using Coulomb's law, which states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. The formula for Coulomb's law is F = k(q1q2/r^2), where k is the Coulomb's constant, q1 and q2 are the charges, and r is the distance between them.

## What is an electric potential?

Electric potential is the amount of electric potential energy per unit charge at a specific point in an electric field. It is measured in volts and represents the work done in moving a unit positive charge from one point to another in the electric field.

## How do I calculate the electric potential due to a point charge?

The electric potential due to a point charge can be calculated using the formula V = k(q/r), where V is the electric potential, k is the Coulomb's constant, q is the charge of the point charge, and r is the distance from the point charge to the point where the electric potential is being calculated.

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