Homework Help: physics

Posted by ashley --- HELP PLEASEE!!! on Wednesday, May 11, 2011 at 8:22pm.

Two point charges +4q and +q are placed 30 cm apart. At what point on the line joining them is the electric field zero?
(a) 15 cm from charge 4q
(b) 20 cm from charge 4q
(c) 7.5 cm from charge q
(d) 5 cm from charge q

physics - drwls, Wednesday, May 11, 2011 at 8:48pm
The distance to the +q charge must be half the distance to the +4q charge, so that the electric fields cancel. Remember the inverse square dependence upon distance!

That puts you 10 cm from q and 20 cm from 4q.

That happens to be one of your choices.

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