John Carney Jr., age 17, of Pocatello, Ida., for his question:

WHAT IS A FARAD?

A farad is a unit of electrical capacity. The farad is named for the great English physicist Michael Faraday.

Here's how you pronounce farad: FAIR ud.

The charge in any condenser is directly proportional to the applied

voltage. If one coulomb of electricity gives a condenser an electrical pressure or potential difference of one volt, the capacity of the condenser is one farad.

For practical purposes, one millionth of a farad, called a microfarad (mF), is used.

In radio and electronic work, one millionth of a mocrofarad is often used. Physicists call this unit a picofarad (pF).

Michael Faraday, who lived from 1791 until 1867, discovered the principle of electromagnetic induction. He found that moving a magnet through a coil of copper wire caused an electrical current to flow in the wire. The electric generator and the electric motor are based on this principle.