‰  NOW 35 WPM  ‰  TEXT IS FROM NOVEMBER 2012 QST  PAGE 70‰

HANDS ON RADIO H. WARD SILVER, NXAX, N0AX ARRL. ORG  EXPERIMENT 118 THE
LAWS AT WORK LAST  MONTHS COLUMN ENDED IN THE YEAR 1831 AS MICHAEL FARADAY
DISCOVERED ELECTROMAGNETIC INDUCTION.  IN FACT, THE DAY ON WHICH I FINISHED
THIS COLUMN WAS THE 181ST ANNIVERSARY OF THAT DISCOVERY AUGUST 29TH.  AS A
REVIEW, FARADAY SHOWED HOW CHANGING CURRENTS IN ONE CIRCUIT COULD INDUCE
SIMILARLY CHANGING CURRENTS IN ANOTHER CIRCUIT WITHOUT ANY DIRECT
CONNECTION BETWEEN THEM.  THIS OCCURS BY FIRST CONVERTING THE FIRST
CIRCUITS ELECTRICAL ENERGY INTO MAGNETIC ENERGY IN THE SURROUNDING FIELD
AND THEN BACK INTO ELECTRICAL ENERGY IN THE SECOND CIRCUIT.
ELECTROMAGNETIC INDUCTION IS DESCRIBED BY FARADAYS LAW AS EXPLAINED IN LAST
MONTHS COLUMNR.  THE FASTER THE MAGNETIC FLUX CHANGES BECAUSE OF MOTION OR
CHANGES IN CURRENT, THE LARGER THE VOLTAGE THAT IS INDUCED IN THE OTHER
CIRCUIT.  THE MINUS SIGN IN FARADAYS LAW GIVES RISE TO LENZS LAW THE
ELECTROMOTIVE FORCE EMF INDUCED BY THE CHANGING MAGNETIC FIELD CAUSES
CURRENT TO FLOW IN THE DIRECTION THAT CREATES A MAGNETIC FIELD OPPOSING THE
ORIGINAL CHANGE IN MAGNETIC FLUX.  LENZS LAW DESCRIBES THE BACK EMF WE
OBSERVE IN MOTORS AND THE KICKBACK VOLTAGE IN A RELAY COIL WHEN IT IS
DEENERGIZED.  LAST MONTHS FIGURE 3 SHOWS THE RELATIVE DIRECTION OF THE
CURRENTS IN BOTH CIRCUITS.  THERE ARE SEVERAL WAYS TO CAUSE THE MAGNETIC
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ