Point Charge Question!

[smunger81]

I would really appreciate some help on this one...I'm pretty sure I'm making it harder than it is...

The question is this - "Three point charges are fixed to the corners of a square, one to a corner, in such a way that the net electric field at the empty corner is zero. Do these charges all have the same sign or the same magnitude but perhaps different signs?"

My answer is the charges would have the same sign and different magnitudes because when calculating net electric fields the sign of the charge is not taken into account...is this right?

Any advice would be fabulous! Thank you!

[mukundpa]

Sorry,
Let the empty corner is the origin and the three other points are (0, -a) (-a, 0) and (-a,-a). If all charges are having same sign (say +) then the forces are along y, x and bisector of x and y respectively. hence the charges must have different sign.

Actually the diagonally opposite corner must have one type of charge and the others have opposite type of charges.

Negative sign of the charge changes the direction of electric field which is a vector quantity.

[smunger81]

Thank you for your help. I was making it waay to hard.