Calculating Where Electric Field Between Two Charges is equal to Zero

In summary: E=K \frac{q}{r^2}(Also remember the direction: the electric field of a positive charge points away from the charge) Pick a point between the two charges - say, at a distance r1 from charge #1 - and calculate the electric field produced by charge #1 at that point. Then calculate the electric field produced by charge #2 at that point. The total electric field at that point is the sum of those two electric fields (but do remember to take direction into account! If the fields point in opposite directions, they subtract, instead of adding)
  • #1
Brodo17
18
0
Two carges of + 1.5 x 10 ^-6 C and + 3.0 X 10^-6 C are .20m apart. Where is the electric field between them equal to zero?


Do I use the equation Kq2/r^2 ? I also have Kq1q2 / r^2
I am pretty sure the problem can be solved using those two equations, and most likely the first equation



Im sorry but I really don't know how to figure this out. I tried to somehow figure it out by finding how much force the first charge is exerting on the second, and vice versa and then subtracting the smaller force from the larger. I don't see how that helps me though.
This question is not for marks, I just really need to learn how to do it today for my test tommorow. Please Help!
 
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  • #2
The first formula is the electric field strenghty of q2 at a distance r. What you want to solve is [itex]E_1+E_2=0[/itex]. Can you find expressions for [itex]E_1, E_2[/itex]?

Edit: made a pretty big "braino"
 
Last edited:
  • #3
Hi Brodo17! :smile:

(try using the X2 and X2 tags just above the Reply box :wink:)
Brodo17 said:
Two carges of + 1.5 x 10 ^-6 C and + 3.0 X 10^-6 C are .20m apart. Where is the electric field between them equal to zero?

Do I use the equation Kq2/r^2 ? I also have Kq1q2 / r^2

Kq2/r22 is the field at distance r2 from charge #2.

Kq1q2/r2 is the force of charge #2 on charge #1 (and vice versa).

You need to use the first equation, twice, with r1 and r2 :wink:
 
  • #4
I don't understand! Could someone please solve the problem and show me the solution.
 
  • #5
Hi Brodo17! Thanks for the PM! :smile:
Brodo17 said:
Thanks for replying to my forum, however if you understand how to get the answer could you show exactly how to do it.
It isn't for marks

Sorry, but you have to make an effort yourself …

what are the two equations you get for r1 and r2 ? :smile:
 
  • #6
Look at what tiny-tim said a couple of posts back. The electric field at a distance r from a charge q is
[tex]E = K \frac{q}{r^2}[/tex]
(Also remember the direction: the electric field of a positive charge points away from the charge) Pick a point between the two charges - say, at a distance r1 from charge #1 - and calculate the electric field produced by charge #1 at that point. Then calculate the electric field produced by charge #2 at that point. The total electric field at that point is the sum of those two electric fields (but do remember to take direction into account! If the fields point in opposite directions, they subtract, instead of adding)
 
  • #7
ok so I pick a random point and calculate the force each charge is exerting at that point? I really don't understand where to go from there though.
 
  • #8
Brodo17 said:
ok so I pick a random point and calculate the force each charge is exerting at that point? I really don't understand where to go from there though.

Not exactly.

The charges are a fixed distance apart. That means that the sum of the distance to each must add to that distance.

The force from each - in opposite directions must be equal ... so, construct an equation for the magnitude of the force of 1 is equal to the force from the other. Then exploit the total distance relationship ... then solve.
 
  • #9
Is it okay to get this thread started up again I have the same question and similar difficulties...


Even if I do as you said, and use E=E1+E2, I still have the problem of having either the two variables of r, or no variable I'm so confused.

If I solve for values of E at a specific point and do vector addition I still don't know when they equal to zero...?
 
  • #10
Its okay, i figured it out. I'm an idiot...
 

1. What is the formula for calculating where the electric field between two charges is equal to zero?

The formula for calculating where the electric field between two charges is equal to zero is: R = √(k * (q1 + q2)/E0), where R is the distance between the two charges, k is the Coulomb's constant, q1 and q2 are the magnitudes of the two charges, and E0 is the permittivity of free space.

2. How do you determine the direction of the electric field when it is equal to zero?

The direction of the electric field when it is equal to zero is determined by the relative positions of the two charges. If the two charges are of the same sign, the direction will be away from both charges. If the two charges are of opposite signs, the direction will be towards the charges.

3. Can the electric field between two charges ever be equal to zero?

Yes, the electric field between two charges can be equal to zero at a specific distance, as calculated by the formula mentioned in the first question. This distance is known as the point of equilibrium between the two charges.

4. What factors affect the point where the electric field between two charges is equal to zero?

The point where the electric field between two charges is equal to zero is affected by the magnitudes of the two charges, the distance between them, and the permittivity of free space. Changing any of these factors will result in a different point where the electric field is equal to zero.

5. How is the electric field between two charges related to the distance between them?

The electric field between two charges is inversely proportional to the square of the distance between them. This means that as the distance between the two charges increases, the electric field decreases. At a certain distance, the electric field will be equal to zero, as calculated by the formula in the first question.

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