Homework Help: Physics please clarify

Posted by Mary on Tuesday, September 4, 2007 at 10:05pm.

A charge of +1q is fixed to one corner of a square, while a charge of -3q is fixed to the diagonally opposite corner. Expressed in terms of q, what charge should be fixed to the center of the square, so the potential is zero at each of the two empty corners?

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Physics please clarify - bobpursley, Tuesday, September 4, 2007 at 9:06pm
stop looking for formulas. Voltage is q/distance. It is a scalar, so you add all the contributing charges. In this case,

voltage at empty corner= voltage from each charge
0= q/s -3q/s + x/d
where s is the side distance, and d is the distance from the empty corner to the center. d=.707s.
solve for x.

I am sorry for being such a bother,I appreciate all of the help you've given to me but I am still not getting this one! I think I am over thinking this problem. This is what i did so far please tell me if I am on the right track:

q/s - 3q/s + X/d = 0

-2q/s + X/d = 0

X/d = 2q/s

X= (2q/s)(d)

from here I am stumped.

Physics please clarify - drwls, Wednesday, September 5, 2007 at 6:05am
I answered this once before. You have a geometrical relationship between a and s, d=.707s , so d/s can be converted to a constant. This gives you an equation that relates X to q.

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