#### The magnitude of the force

Two equal charges Q are placed a certain distance apart. They exert equal-and-opposite forces F on one another. Now one of the charges is doubled in magnitude to 2Q. What happens to the magnitude of the force each charge experiences?

- Both charges experience forces of magnitude 2F.
- The Q charge experiences a force of 2F; the 2Q charge experiences a force F.
- The Q charge experiences a force of F; the 2Q charge experiences a force 2F.
- None of the above.

Both forces are now 2F. It doesn't matter which charge you consider, the force is given by:

Coulomb's law: F = kQ(2Q) / r^{2}

Another good way to explain this is to remember Newton's Third Law, which says that the forces objects exert on one another are equal-and-opposite.