Coulomb's Law - Electrostatics

[sally2442]

Hey.

I only just started this unit at school (after coming back from holidays and forgetting everything!) and I'm having trouble with the following problem:

Homework Statement

"Four point charges A, B, C and D are arranged on the corners of a square of side 25cm. If A and B each have a charge of +1 uC while C and D each have a charge of +2 uC, what is the resultant force on a charge of +1 uC placed at the centre of the square?"

Homework Equations

Coulomb's Law
f = k((Q1*Q2)/d2)

where f = force, k = 9x10^9, Q1 and Q2 are the charges in coulombs and d is the separation of the charges (m)

The Attempt at a Solution

I attempted the question, not really knowing where to begin, and got some really weird (and definitely incorrect) answers. It's probably simple and I'm just really slow .

I'd really love if someone could just outline where I start and what processes to use to get the answer so I can apply it to other problems.

Thanks so so much!

 

[likephysics]

Calculate individual force on the charge (F_a, F_b...), then add the total force as a vector.

 

[thomate1]

Hi there,

Don't worry, Coulomb's Law can be tricky to understand at first. Let's break down the problem step by step.

First, we need to find the distances between the charges. Since they are arranged on the corners of a square, we can use the Pythagorean theorem to find the distance between the center and each corner. This will give us a distance of 17.68 cm for each of the four charges.

Next, we can use Coulomb's Law to calculate the force between each pair of charges. Remember, the force is attractive if the charges have opposite signs and repulsive if they have the same sign. So, for the pair A and B, the force will be repulsive and for the pair C and D, the force will be attractive.

Now, we can use vector addition to find the resultant force on the charge at the center. Since the forces are acting in different directions, we need to use the Pythagorean theorem again to find the magnitude of the resultant force. Once we have the magnitude, we can use trigonometry to find the direction of the force.

I hope this helps! Remember to always break down the problem into smaller steps and use the appropriate equations. Good luck with your studies!