Where Is the Electric Field Zero Between Two Charges?

[brandon26]

Homework Statement

Two charges of value +4C and -16C are separated by a distance of 3m.

At what spot along the line is the electric field is zero?

Homework Equations

I tried using the equation E = Q / 4pieE(o)r^2

The Attempt at a Solution

I get a quadratic equations which cannot be solved, please help me out. It is very urgent.

 

[cristo]

Well, what specifically did you do? If you show your work, it will be easier to help!

 

[Hootenanny]

I get a quadratic equations which cannot be solved, please help me out. It is very urgent.

I assure you that it can be solved, perhaps if you showed you working...

Edit: Damn, your quick cristo. It seems roles have been reversed...

 

[cristo]

Edit: Damn, your quick cristo. It seems roles have been reversed...

Haha, I beat you to it for once, about time too! Although I wouldn't say roles were reversed just yet

 

[robphy]

Before writing equations, you might ask yourself:
- will it be between the charges? if not, on which side will it be?
- will it be equidistant from each charge? if not, which charge is it closer to?

(Hint: think physically: what would a third charge feel at this point you seek?)

(Hint: Although you can write down one [fancy] equation that you can solve, you probably won't. The above suggest cases to consider and some intuition to almost guess the numerical solution.)

 

[brandon26]

GOD! This website is soo useless!

 

[cristo]

GOD! This website is soo useless!

Brandon, please see here: https://www.physicsforums.com/showthread.php?t=94379, with specific reference to point 1)

1) Did you show your work? Homework helpers will not assist with any questions until you've shown your own effort on the problem. Remember, we help with homework, we don't do your homework. We already passed those classes; it's your turn to do so.

You must show your work before we can help you; this means the actual equations you used, not simply a brief "I used this method" type expression.

 

[thephy]

Robphy is helping you to think and solve the problem by yourself.

Details:
1) since 16C >4C, the third spot should be closer to +4C
2) the spots between the two charges could not be 0, since in this case, the field of the two charge is in the same direction.

Thus, the spot should in the left of +4C.

The equation should be 4/x^2=16/(3+x)^2.

It does have a solution.

 

[brandon26]

this is exactly what I got, except for one small difference. The charge of the second particle is negative, why have u ignored it??

 

[brandon26]

actually...i js noticed your second point... both charges act in the same direction so the null point can't be inbetween the charges.

But why have you ignored the negative sign ??

 

[robphy]

Draw a free-body diagram.

 

[brandon26]

I have put it still doesn't make sense. You cannot ignore the negative sign, can you?