Finding the neutral point of two charges

AI Thread Summary
The discussion focuses on finding the neutral point between two charges, q1=+9c and q2=-1c, separated by 2m. The electric field equations are set up correctly, but confusion arises when solving for the neutral point, particularly when encountering a negative square root. Participants clarify that the electric field direction must be considered based on the charges' positions, leading to the conclusion that the neutral point is nearest to the negative charge. After simplifying the equations, the solution reveals that the neutral point is at x=1m. This method effectively demonstrates how to approach the problem using electric field concepts.
kspabo
Messages
19
Reaction score
0

Homework Statement


Two charges q1=+9c and q2+-1c are separated by 2m. Where is their neutral point?

Homework Equations


E = E(+) + E(-)
E= k q/r^2

The Attempt at a Solution


k q1/(2+x)^2 = -(k q2/x^2)

When I solve for this equation I end up square rooting a negative number which would then give i and I don't know how to work with this.
 
Physics news on Phys.org
kspabo said:

Homework Statement


Two charges q1=+9c and q2+-1c are separated by 2m. Where is their neutral point?

Homework Equations


E = E(+) + E(-)
E= k q/r^2

The Attempt at a Solution


k q1/(2+x)^2 = -(k q2/x^2)

When I solve for this equation I end up square rooting a negative number which would then give i and I don't know how to work with this.
Doesn't the electric field vector point away from a positive charge and towards a negative charge?

If so, the sign you use for the field from each of your charges depends upon the position relative to the charges.
 
SammyS said:
Doesn't the electric field vector point away from a positive charge and towards a negative charge?

If so, the sign you use for the field from each of your charges depends upon the position relative to the charges.
Correct. So the positive field flows right towards the negative which continues a field to the right. I'm looking for the neutral point nearest the negative charge. How can I use this info to solve this if q1 is at 0 and q2 is at x=2?
 
Last edited:
kspabo said:
Correct. So the positive field flows right towards the negative which continues a field to the right. I'm looking for the neutral point nearest the negative charge. How can I use this info to solve this if q1 is at 0 and q2 is at x=2?
Show what you get when you put values for charge into the following and do a little simplifying.
kspabo said:
k q1/(2+x)^2 = -(k q2/x^2)

Also,
What is the quadratic equation you get?
 
SammyS said:
Show what you get when you put values for charge into the following and do a little simplifying.Also,
What is the quadratic equation you get?

k q1/(2+x)^2 = -(k q2/x^2)
q1/(2+x)^2 = -(q2/x^2)
+9/(2+x)^2 = -(-1/x^2)
9/(2+x)^2 = 1/x^2
x^2/(2+x)^2 = 1/9
x/(2+x) = ± 1/3
(2+x)/x = ± 3
2/x + 1 = ± 3
2/x = -1 ± 3
So we have x=1 when -1 + 3

Ah, that makes sense and I believe is the correct answer.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

Induction confusion for induced charge inside a metal conductor
Replies
23
Views
937
How Can Two Point Charges Be Arranged to Nullify Electric Field at the Origin?
Replies
9
Views
4K
Understanding E=F/q: Solving for E at a Specific Point q_p
Replies
13
Views
1K
Neutral Point between point charges
Replies
12
Views
5K
Electric Field due to multiple point charges
Replies
2
Views
4K
Charge conservation for 3 parallel charged plates
Replies
19
Views
1K
Gauss' Law question about a conducting rod
Replies
3
Views
2K
A positive charge of magnitude Q1 = 8.5 nC is located....
Replies
2
Views
8K
Solving Electric Field with 3 Point Charges: Find q1 & q2
Replies
8
Views
2K
Electric field created by point charges
Replies
6
Views
812

Hot Threads

Recent Insights

Back
Top