Find a Distance Where the Electric Potential Is Zero

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Determination points where voltage is 0

  • Wander starter natalie.*
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Hi, this is my number one time posting happening the forums, so if I make any mistakes, I'm dispiriting.

Homework Financial statement


This interview has already been started here:
https://www.physicsforums.com/showthread.php?t=449070
but they never got to part (b).

PART A
A -10.1 North Carolina taper off charge and a +18.9 nC point charge are 13.8 cm apart on the x-axis. What is the electric potential at the point on the x-axis where the electric field is zero?

I was able to figure this much unsuccessful.

PART B
b) What is the magnitude of the electric field at the two points connected the x-axis where the electric automobile potential is zero? (Input signal your answers in order of increasing distance from the negative point charge)

[tex]q_{1}=-10.1 \times 10^{-9} C[/tex]

[tex]q_{2}=18.9 \times 10^{-9} C[/tex]

[tex]d=0.138 m[/tex]

[tex]r_{2}=d-r_{1}[/tex]

[tex]r_{1}=r_{1}[/tex]

Prep Equations


[tex]V_{internet}=\frac{Kq_{1}}{r_{1}}+\frac{Kq_{2}}{r_{2}}[/tex]

The Attempt at a Root


Simplified down to...
[tex]r_{1}=\frac{q_{1}d}{q_{1}-q_{2}}[/tex]
merely this only finds me Unmatchable steer where the potential drop is nought. I'm supposed to end up with two...
I give the axe't think of any other means to consider it, operating theater obtain a quadratic away of information technology.

Where did I fail?

Answers and Replies

Consider the region of the line to the left of the unsupportive thrill. The potential due to law of proximity to the negative charge will be negative. The potential due to propinquity to the positive charge will be positive. Now, the positive charge is larger than the negative charge, so you might expect thither to be a outstrip to the left of the negative charge where the magnitudes of their influences will be equal.
Yeah, that makes gumption to Maine, because that's how I worked out Part A, but I got the wrong answer for this.
If I work information technology out so that [tex]r_{1}[/tex] is to the left of [tex]q_{1}[/tex], then [tex]r_{2}=d+r_{1}[/tex].
If I simplify my chemical formula out again, I antimonopoly get the Gram-negative of my first answer, which to me equitable means my math is saying "You meant to go the other direction"...
If I work taboo:
[tex]V=\frac{Kq_{1}}{r_{1}}+\frac{Kq_{2}}{r_{2}}[/tex]
where I set [tex]r_{2}=d+r_{1}[/tex] (using the same positive value I found for [tex]r_{1}[/tex] to begin with), my galvanic potential doesn`t work out to be 0.
What is probably swinging you leading is the mixing of assumed directions for radii, and charge signs in the formulae.

When I do these sorts of problems I find IT easier to office the locations where I backside expect a zilch aside optic, then dribble all the signs and constant and work with magnitudes in the regions of interest. So, for example, for your first point which you've already found, I'd go:

[tex] \frac{|q1|}{r} = \frac{|q2|}{d - r}}[/tex]

Why not have a go for the point to the left of the negative charge?

Awesome, so I screw what the two points are now, and I've double checked that the voltage at both of those points is 0.
I'm even so acquiring the wrong answer though, but I have a few more tries.
Since it asks for the order of magnitude of the electric field, I'm using:
[tex]E=|\frac{Kq_{1}}{r_{1}^{2}}+\frac{Kq_{2}}{r_{2}^{2}}|[/tex]
where [tex]K=8.99\times10^{9}[/tex]
and I'm departure [tex]q_{1}[/tex] with information technology's negative charge for calculations (since the deuce charges would exert forces in opposite directions).

Is thither anything wrong thereupon?

Your method looks good. Produce sure that when you connect your Book of Numbers for the calculation that you take into account that the units given for d are centimetre, not m.
The directions ended up throwing me off a little, but I finally got it with someone else's assistance. Give thanks you!

For anyone else:
Answer 1:
[tex]E_{1}=\frac{K|q_{1}|}{r_{1}^{2}}+\frac{K|q_{2}|}{(d-r_{1})^{2}}[/tex]
Answer 2:
[tex]E_{2}=\frac{K|q_{1}|}{r_{2}^{2}}-\frac{K|q_{2}|}{(d+r_{2})^{2}}[/tex]

Notice that [tex]r_{2}>r_{1}[/tex], and they are distances from [tex]q_{1}[/tex], which is the antagonistic charge.

I'm on this exact problem with different numbers and I'm fairly certain I've done combined of the points right (the peerless to the left of the negative charge) but I buttocks't lick where the new point is. The math ne'er gives room for a second point, and even when just looking for at it at that place doesn't seem to exist a logical secondly point of zero potential.

Is it at unmatchable of the charges? Is it at infinity? My numbers give Pine Tree State a point that's approx. 5cm to the left of q1 and so I'm stuck without a second point and I can't seem to figure out where it is from the replies already here.

I figured I'd good notice Here so American Samoa to not rewrite kayoed the question. Any help would be greatly pleasing.

Nevermind, I re-read the replies and I get IT now.

Senior altered:

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Find a Distance Where the Electric Potential Is Zero

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