Janet Seidel, age 15, o Vancouver, Wash., for her question:

WHAT IS A FARAD?

A farad is a unit of electrical capacity.

A coulomb is the meter kilogram second unit of electric charge that is equal to the quantity of charge transferred in one second by a constant current of one ampere. If one coulomb of electricty gives a condenser an electrical pressure or potential difference of one volt, the capacity of he condenser is one farad.

For practical purposes, one millionth of a farad, called a microfarad (mF), is used. In radio an electronic work, one millionth of a microfarad is often used. Physicists all this unit a picofarad (pF). The farad is named for the great English physicist and chemist Michael Faraday. In 1831, he discovered the principle of electromagnetic induction. Faraday found that moving a magnet through a coil of copper wire caused an electric current to flow in the wire. The electric generator and the electric motor of today are based on this principle.

Faraday's work in electrochemistry led him to discover a mathematical relationship between electricity and the valence or combining power of a chemical element. It gave the first clue to the existence of electrons.