Charlie McEvoy, age 13, of Fredericton, New Brunswick, Canada, for his question:

WHAT IS AN AMPERE?

An ampere is the unit used to measure the rate of flow of an electric current. Electric current flows at the rate of one ampere when one coulomb (the unit of electric charge) flows past a section of an electric circuit in one second. Because of this, one ampere equals one coulomb per second.

Physicists define amperes in terms of the magnetic force, measured in newtons.

A 100 watt light bulb takes about one ampere of current. Sensitive scientific instruments use current measured in microamperes, which are millionths of amperes. Large industrial equipment uses current measured in kilo amperes, which are thousands of amperes.

The name ampere honors the French scientist Andre Marie Ampere who studied current.