‰  NOW 30 WPM  ‰  TEXT IS FROM NOVEMBER 2012 QST  PAGE 70‰

FIELD LINKING THE TWO COILS TO CHANGE.  THE MOST OBVIOUS WAY IS TO SIMPLY
TURN THE CURRENT GENERATING THE FIELD ON AND OFF WITH A SWITCH.  ANOTHER
WAY IS TO MOVE ONE OF THE COILS SO IT ENCOUNTERS MORE OR LESS OF THE
MAGNETIC FIELD.  THIS IS THE PRINCIPAL BEHIND AN ELECTRICAL AC GENERATOR.
AN ARMATURE COIL IS ROTATED INSIDE A CURRENT CARRYING STATIONARY COIL OR
STATOR CAUSING THE ARMATURE VOLTAGE TO VARY AS A SINE WAVE.  SIMILARLY,
CHANGING THE CURRENT IN THE STATOR CAUSES THE ARMATURE TO TURN, CREATING A
MOTOR.  IN THIS MONTHS COLUMN WE WILL FOLLOW IN THE STEPS OF PIONEERS ANDRI
MARIE AMPHRE, HANS CHRISTIAN ORSTED AND FARADAY BY PERFORMING SOME SIMPLE
EXPERIMENTS DEMONSTRATING THE VARIOUS EFFECTS THEY DESCRIBED.  IS THIS
PURELY A HISTORICAL EXERCISE?  NOT AT ALL.  THESE PHENOMENA ARE AT THE
HEART OF RADIO WITHOUT THEM WE WOULD BE WIRELESS LESS.  EXPERIMENT 1
ORSTEDS OBSERVATION DURING A LECTURE, WITH EXPERIMENTAL APPARATUS SCATTERED
ACROSS A TABLE, ORSTED NOTICED THAT A COMPASS NEEDLE DEFLECTED AWAY FROM
NORTH WHEN HE SWITCHED CURRENT ON AND OFF IN A NEARBY CIRCUIT.  THIS WAS
THE FIRST OBSERVATION LINKING ELECTRICITY AND MAGNETISM AND IT WAS THE
‰  END OF 30 WPM TEXT  ‰  QST DE W1AW  ƒ