A charge q is placed at the centre of the line joining two equal charges Q.The sysytem of the three charges will be in equilibrium if q is equal to......

Question

kainui · Answer

Consider that two equal charges also have the same sign and magnitude, so they will repel each other away. In order to cancel this out, you're going to need a charge that is of opposite sign and of a certain ratio of the magnitude of the charges to resist their pull on each other.

Draw a picture and see what is needed to equal them out.

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You can see that you have two forces acting on the particle to the right, one by the particle on the other end of the same sign and then the one in the middle. Since you know force is based on charge and distance, but that the distance is already set, you can start to work out how to solve this problem so to set the particles in equilibrium.