(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Two particles are fixed to an x axis, particle 1 of charge q1 = 2.1x10^-7 C at x = 20cm and particle 2 of charge q2 = -4.00q1 at x = 70cm. At what coordinates on the axis is the net electric field produced equal to 0?

2. Relevant equations

3. The attempt at a solution

First, I noted that E1 + E2 = 0, so E1 = -E2.

Then, factoring out k = 8.99x10^9, I am left with:

[itex]\frac{q_{1}}{r^{2}_{1}} = -\frac{q_{2}}{r^{2}_{2}} [/itex]

[itex]\frac{q_{1}}{r^{2}_{1}} = \frac{4q_{1}}{r^{2}_{2}} [/itex]

[itex]\frac{r_{2}}{r_{1}} = 2 [/itex]

I interpreted this to mean that the charge must be twice as far from q2 as it is from q1.

So then,

x - 70 = 2(x-20)

x = -30cm

Which is what the book says, but in my method there are other solutions too, like

x - 70 = 2(20-x)

x = 36.6666

Are these other solutions valid? Can the coordinate be ANY such that it is twice as far from q2 as it is from q1?

I may have solved this in a weird way, its because I'm doing it on my own and didn't take the class yet.

Thanks again!

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# Homework Help: Find the coordinate where net electric field is 0

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