(adsbygoogle = window.adsbygoogle || []).push({}); 1. Problem1 statement, all variables and given/known data

In the figure particle 1 of charge q1 = -8.13q and particle 2 of charge q2 = +3.63q are fixed to an x axis. As a multiple of distance L, at what coordinate on the axis is the net electric field of the particles zero?

http://img201.imageshack.us/img201/4669/netfieldzeromy7.gif

2. Relevant equations

Electric Field = k|q| / r²

The attempt at a solution

Since it's a point between the two charged particles, let x = the distance between q1 and that point, so the distance between the point and q2 = L - x

http://img157.imageshack.us/img157/990/netfieldzero2xj8.gif

The net electric field = 0,

so -(Electric field due to q1) + (Electric field due to q2) = 0

E1 is negative because q1 is negative, E2 vice versa.

-( k|-8.13q| / x² ) + ( k|3.63q| / (L - x)² ) = 0

Cancelling, etc gives:

4.5x² - 16.26Lx + 8.13L² = 0

quadratic formula gives: x = 0.6L or 3.01L

I got it wrong, I'm also confused about the sign of the electric fields but the quadratic formula won't produce a real solution if both fields were negative or positive.

1. Problem2 statement, all variables and given/known data

Charge is uniformly distributed around a ring of radius R = 2.41 cm and the resulting electric field is measured along the ring's central axis (perpendicular to the plane of the ring). At what distance from the ring's center is E maximum?

2. Relevant equations

Electric Field of Ring = (kqx) / ( (x² + k²) ^ (3/2) )

The attempt at a solution

I attempted to differentiate the equation with respect to x and put E' = 0, but I have two unknowns, x and q, the solution is a real number with no variables.

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# 1.) Net electric field and 2.) Maximum electric field from centre of a ring

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