The diagram shows two charged particles. Red indicates a positive charge. Blue indicates a negative charge. Will the two particles in the diagram attract or repel each other?
Okay, we’re told that the charged particle which is coloured in red is a positive charge and the one in blue is a negative charge. The question is when these two particles interact, will they attract or repel one another; that is, will they draw one another together or push one another apart. Before we answer that question, notice something interesting about this setup.
Because we have two charged particles, that means we have two electric fields. After all, each particle creates its own electric field. That means the field created by the negative charge impacts the positive charge and the field created by the positive charge affects the negative charge. To figure out what this overall effect will be, we can recall a rule for electric charge interaction.
This rule tells us how electric charges in their most basic form interact with one another. In general, there are three varieties or possibilities for pairing electric charge. The first possibility is that the charges have an opposite sign: one positive, one negative. The next possibility is that they have the same sign: both positive. And lastly, both of the charges could have a negative sign.
In the case of the first pair, experiments have shown us that these charges attract one another. They’re drawn in towards their common centre. The other two pairs, it turns out repel one another. But really, it’s this first pair which is of interest to us. That matches our setup. This tells us that the negative charge in our scenario will be drawn towards the positive charge and the positive charge will be drawn towards the negative.
And that’s our answer: we can see that the two particles will attract each other. That’s how a positive and a negative charge will interact.