"Annenberg Media" "¶" "IN 1820, HANS CHRISTIAN OERSTED MADE HIS GREAT DISCOVERY" "OF HOW TO TURN ELECTRICITY INTO MAGNETISM." "AT THAT POINT," "EVERY SCIENTIST IN EUROPE" "KNEW THERE WAS ANOTHER GREAT DISCOVERY" "WAITING TO BE MADE," "AND THAT WAS HOW TO USE MAGNETISM" "TO CREATE ELECTRICITY." "THEY ALSO KNEW THAT WHOEVER MADE THAT DISCOVERY" "WOULD BECOME IMMORTAL," "AND SO ALL OF THEM SCURRIED BACK TO THEIR LABORATORIES" "AND WENT TO WORK." "THEN 12 YEARS PASSED, AND NOTHING HAPPENED." "NOW, 12 YEARS IS A LONG TIME." "FOR MOST OF YOU, 12 YEARS IS 2/3 OF YOUR LIVES." "IT'S NEARLY 1/2 OF MY LIFE," "AND YET, IN ALL THAT TIME, THE DISCOVERY WAS NOT MADE." "NOW, IN SCIENCE, ONCE YOU UNDERSTAND SOMETHING," "IT'S VERY DIFFICULT TO REMEMBER WHAT IT'S LIKE" "NOT TO HAVE UNDERSTOOD IT." "THE FACT IS THAT DURING THAT PERIOD," "MANY EXPERIMENTS WERE DONE" "THAT HAD THE DISCOVERY IN THEM" "IN COMPLICATED WAYS THAT COULDN'T BE UNDERSTOOD," "BUT ONCE THE DISCOVERY WAS MADE AND REDUCED TO THE ESSENCE," "IT'S JUST AS SIMPLE AS IT CAN POSSIBLY BE." "HERE I HAVE A SIMPLE LOOP OF WIRE." "MY JOB IS TO MAKE AN ELECTRIC CURRENT" "RUN AROUND IN THIS LOOP." "THE LOOP'S CONNECTED TO A GALVANOMETER WHOSE OUTPUT" "IS THAT POINT OF LIGHT." "IF I MAKE THE CURRENT RUN THROUGH THE LOOP," "THAT LIGHT WILL MOVE." "HOW WILL I MAKE IT WORK?" "USING MAGNETISM." "HERE I HAVE A BAR MAGNET." "TO USE THIS MAGNET TO MAKE A CURRENT RUN AROUND THIS LOOP" "IS VERY EASY." "I JUST MOVE THE LOOP INTO THE MAGNET" "OR, FOR THAT MATTER, BACK OUT AGAIN." "THAT WAS IT, THE GREAT DISCOVERY." "ONE THING MORE" "IF I MOVE THE LOOP BACK AND FORTH," "THEN THE CURRENT RUNS BACK AND FORTH" "AND KEEPS ON GOING." "VIRTUALLY ALL ELECTRIC POWER, ONE WAY OR ANOTHER," "IS GENERATED BY THAT MECHANISM." "IN OTHER WORDS," "THAT DISCOVERY IS THE VERY BASIS" "OF OUR ELECTRICAL CIVILIZATION," "AND THAT'S OUR SUBJECT FOR TODAY." "WITHOUT ENERGY, CIVILIZATIONS GO NOWHERE," "NOT EVEN IN CIRCLES," "BUT WITH A STRONG AND STEADY WIND" "AND A COMPARATIVELY SIMPLE MACHINE," "AN ENDLESS SUPPLY OF POWER CAN FLOW JUST ABOUT ANYWHERE," "AND ONCE IT'S BEEN CONVERTED TO ELECTRICITY," "ACCOMPLISH WHAT THE ANCIENTS PROBABLY NEVER EVEN IMAGINED." "THESE DAYS, IT LOOKS EASY ENOUGH ON THE SURFACE," "BUT TO UNDERSTAND HOW WIND MAKES ELECTRICITY," "IT'S NECESSARY TO DIG A LITTLE DEEPER" "AND TO COME UP WITH A BIT OF HISTORICAL PERSPECTIVE." "THE DUTCH WERE MASTERS WHEN IT CAME TO WINDMILLS." "HOLLAND HAD MORE WATER" "AND LESS CULTIVATED LAND THAN SHE NEEDED," "SO NECESSITY BECAME THE MOTHER OF INVENTION," "AND THE DUTCH BECAME VERY GOOD" "AT USING THE WINDMILL TO TURN THE RHINE RIVER DELTA" "INTO GOOD, DRY FARMLAND." "BUT BY THE 1800s," "ANOTHER KIND OF REVOLUTION WAS IN THE AIR," "AND IT WAS THE CHURNING POWER AND GLORY OF STEAM." "FOR ALL THEIR MAJESTY," "THE FUTURE BELONGED NOT TO WINDMILLS," "BUT TO STEAM ENGINES" "FIRED BY THE MINERAL SOLID CALLED COAL." "COAL WAS INEXPENSIVE," "AS STEADY AS A ROCK," "AND AS CONVENIENT AS THE CLOSEST RAILROAD TRACK," "SO FOR A WHILE THERE, COAL WAS REALLY COOKING." "HOWEVER, IN COMMERCE AND CHEMISTRY ALIKE," "FEW THINGS HAVE EVER REMAINED THE SAME FOR LONG," "AND EVEN AS COAL WAS GATHERING STEAM" "IN THE INDUSTRIALIZED NATIONS," "A NEW AND DIFFERENT ELEMENT ENTERED THE PICTURE." "IT WAS CALLED ELECTRICITY." "NOWHERE WAS IT MORE HOTLY PURSUED" "THAN AT THE ROYAL INSTITUTION IN LONDON," "AND NO ONE HAD PURSUED IT MORE CLOSELY" "THAN THE 18th CENTURY'S MOST DILIGENT" "AND INTUITIVE SCIENTIST, MICHAEL FARADAY." "HE PROBED THE MYSTERIES OF SCIENCE" "BECAUSE, FOR HIM, THE BUILDING BLOCKS OF NATURE" "HAD BEEN CREATED WITH A FUNDAMENTAL UNITY." "AND MR. FARADAY BELIEVED" "THAT THE BLUEPRINT WAS TO BE FOUND" "WITHIN THE LAWS OF PHYSICS." "WITH THAT BELIEF," "FARADAY WAS MOTIVATED TO UNEARTH A NEW LINK" "BETWEEN TWO OF MOTHER NATURE'S FUNDAMENTAL FORCES" "MAGNETISM AND ELECTRICITY." "HIS QUEST BEGAN IN 1821" "WITH HANS CHRISTIAN OERSTED'S DISCOVERY" "THAT THE FLOW OF AN ELECTRIC CURRENT" "CREATES A MAGNETIC FIELD." "FIRST, FARADAY REPRODUCED THE EXPERIMENT," "AND THEN, IN A ROUNDABOUT WAY," "HE TOOK A MAJOR STEP FORWARD." "HE INVENTED A DEVICE THAT KEPT TWISTING" "AS IT FOLLOWED THE CIRCULAR MAGNETIC FIELD" "CREATED BY A CURRENT." "FROM THIS POINT ON," "WHEN PEOPLE THOUGHT OF THINGS TURNING TO CREATE POWER," "THEY NO LONGER THOUGHT" "OF WINDMILLS AND STEAM ENGINES ALONE." "WITH THIS AMAZING DEVICE," "AN ELECTRIC CURRENT COULD CREATE PHYSICAL WORK." "IN OTHER WORDS," "THIS WAS THE WORLD'S FIRST ELECTRIC MOTOR." "BUT FARADAY'S RESTLESS MIND" "SAW MORE THAN CIRCLES OF MAGNETIC FORCE" "IN OERSTED'S DISCOVERY." "HE SAW A CRUCIAL SCIENTIFIC QUESTION." "IF AN ELECTRIC CURRENT COULD CREATE A MAGNETIC FIELD," "COULD A MAGNETIC FIELD CREATE AN ELECTRIC CURRENT?" "THE ANSWER DIDN'T COME EASILY." "IT TOOK LAMP OIL AND PAPER," "BRILLIANCE AND TENACITY," "UNTOLD COMBINATIONS OF COILS, MAGNETS, AND WIRES." "IT TOOK MORE THAN A DECADE," "WHICH IS WHY BIOGRAPHERS NOTE HIS "LENGENDARY PATIENCE,"" "BUT IN 1831, MICHAEL FARADAY HAD THE ANSWER." "AS HE CONNECTED A BATTERY TO ONE COIL," "CURRENT FLOWED BRIEFLY IN ANOTHER COIL." "HE'D FOUND THE ANSWER," "AND IN THE PROCESS, HE'D DISCOVERED" "THE PRINCIPLE OF ELECTROMAGNETIC INDUCTION." "HOW DOES ELECTROMAGNETIC INDUCTION REALLY WORK?" "IN OTHER WORDS," "HOW CAN A MAGNETIC FIELD" "DRIVE AN ELECTRIC CURRENT AROUND A CIRCUIT?" "MAGNETIC FIELDS APPLY FORCES TO ELECTRIC CHARGES," "BUT ONLY IF THE CHARGES ARE IN MOTION." "THE DIRECTION OF THE FORCE IS PERPENDICULAR" "TO THE VELOCITY AND THE FIELD" "AND DEPENDS ON THE SIGN OF THE CHARGE," "IN THIS CASE, NEGATIVE." "FOR EXAMPLE," "THE CHARGES MIGHT BE ELECTRONS IN A PIECE OF WIRE." "JUST MOVING A WIRE THROUGH A MAGNETIC FIELD" "MAKES A CURRENT TRY TO FLOW." "BUT THE FIELD OF A BAR MAGNET" "CAN BE PERPENDICULAR AT EVERY POINT" "TO A CIRCULAR LOOP OF WIRE," "SO MOVING THE LOOP CREATES A FORCE" "THAT DRIVES A CURRENT ALL THE WAY AROUND THE LOOP." "THE CURRENT FLOWS ONE WAY" "IF THE LOOP MOVES UPWARD" "AND THE OTHER WAY" "IF THE LOOP MOVES DOWNWARD." "OF COURSE, A CURRENT ALSO FLOWS IF THE LOOP STANDS STILL" "AND THE MAGNET MOVES..." "ONE WAY IF THE MAGNET MOVES DOWNWARD..." "THE OTHER IF THE MAGNET MOVES UPWARD." "IN FACT, FARADAY FOUND THAT ANY METHOD" "OF CHANGING THE MAGNETIC FIELD THROUGH A CIRCUIT" "WOULD MAKE A CURRENT FLOW." "FOR EXAMPLE, HE COULD INDUCE A CURRENT" "BY MOVING A BAR MAGNET RELATIVE TO A COIL." "WHEN FARADAY CONNECTED A COIL TO A BATTERY," "THE SUDDEN INCREASE IN THE MAGNETIC FIELD" "INDUCED A SURGE OF CURRENT IN ANOTHER COIL." "BOTH THESE IDEAS CAN BE EXPRESSED" "IN TERMS OF MAGNETIC FLUX." "THETOTALMAGNETICFLUX THROUGHA SURFACE" "ISTHEINTEGRALOF THE COMPONENT OF MAGNETIC FIELD" "PERPENDICULAR TOEACHBITOFAREA" "THATMAKESUP  THESURFACE." "ASA LOOPOF WIRE" "MOVESTHROUGHTHEFIELD OFA BARMAGNET," "THE FLUX THROUGH THE LOOP KEEPS CHANGING." "THE CHANGING FLUX CAUSES A CURRENT TO FLOW" "AS IF IT WERE DRIVEN BY A VOLTAGE." "THAT VOLTAGE, CALLED THE ELECTROMOTIVE FORCE, E," "IS EQUAL TO MINUS THE RATE OF CHANGE" "OFMAGNETICFLUX THROUGH THE LOOP." "THAT'S CALLED FARADAY'S LAW OF ELECTROMAGNETIC INDUCTION." "A GENERATION LATER AND A CONTINENT AWAY," "OTHER PIONEERING GENIUSES" "WOULD MAKE THE MOST OF FARADAY'S DISCOVERY." "THEIR NAMES WERE THOMAS EDISON" "AND NIKOLA TESLA." "UNLIKE FARADAY, HOWEVER," "THEIR PRIMARY AMBITION WAS TO MAKE MACHINES WORK" "AND TO MAKE THEM PAY FOR THEMSELVES." "EDISON SAW A LOT OF PROFIT" "IN THE BUSINESS OF ELECTRICITY," "BUT IF HE WERE TO REALIZE IT," "HE'D NEED TO LIGHT UP THE CITY OF NEW YORK." "THAT WOULD REQUIRE A NETWORK OF VERY POWERFUL GENERATORS." "NO MATTER THE ENGINEERING SHAPE THEY'D TAKE," "THE PRINCIPLE OF EVERY DYNAMO" "WOULD COME FROM FARADAY'S LAW OF ELECTROMAGNETIC INDUCTION." "ROTATINGA LOOPOF WIRE" "IN A CONSTANT MAGNETIC FIELD" "CONTINUALLY CHANGES THE FLUX" "THROUGHTHELOOP." "THERESULTINGVOLTAGE" "ANDCURRENTARESINUSOIDAL," "GOINGFIRSTONEWAY ," "THENTHEOTHER." "USING ELABORATE SLIDING CONTACTS" "ATTACHED TO THE ROTATING COILS," "EDISON COULD COMPENSATE FOR THE OSCILLATING VOLTAGE," "DRAWING CURRENT THAT ALWAYS RAN" "IN THE SAME DIRECTION FROM HIS GENERATORS." "TESLA THOUGHT EDISON'S SYSTEM OF DIRECT CURRENT" "WAS COSTLY AND INEFFICIENT" "AND THAT ALTERNATING CURRENT WOULD DO THE JOB BETTER," "BUT AC OR DC, ONE QUESTION REMAINS" "WHICH WAY DOES THE INDUCED CURRENT FLOW?" "CURRENTFLOWS THROUGHA COILOF WIRE" "WHENEVERTHEMAGNETICFLUX THROUGHITIS CHANGING." "THECURRENTFLOWSONE WAY  IFTHEFLUXDECREASES" "ANDTHEOTHERWAY  WHENTHEFLUXINCREASES." "BUTTHECURRENT INDUCEDINTHEWIRE" "ALSOCREATES AFLUXOF ITSOWN ," "WHOSE DIRECTION DEPENDS ON THE DIRECTION OF THE CURRENT." "THEFLUXCREATED BYTHEINDUCEDCURRENT" "ALWAYSOPPOSESTHECHANGE INTHEEXTERNALFLUX." "THISRULEIS KNOWN ASLENZ'SLAW." "THE NET RESULT OF BOTH FIELDS ADDEDTOGETHER" "ISTOSLOWDOWNTHERATE" "AT WHICH THE MAGNETIC FLUX THROUGHANYCIRCUIT" "ISABLETO CHANGE." "AS ELECTRIC POWER GREW MORE IMPORTANT," "LENZ'S LAW DIDN'T SLOW DOWN THE RATE OF CHANGE" "OF TECHNOLOGICAL PROGRESS," "AND STEAM ENGINES WEREN'T OUT OF THE PICTURE," "NOT BY A LONG SHOT." "ENGINES FIRED BY BOTH COAL AND OIL" "CONTINUED TO TURN GENERATORS" "AND CREATE THE POWER OF ELECTRICITY." "HOWEVER, THE MORE THAT COAL AND OIL" "WERE TAKEN AWAY AND USED UP," "THE MORE OBVIOUS IT BECAME" "THAT THE EARTH BEGAN WITH A LIMITED AMOUNT," "AND FOR SOME," "WHEN IT CAME TO FOSSIL FUELS," "THE END WAS ALREADY IN SIGHT," "SO THE SEARCH FOR ALTERNATIVES CONTINUED." "FOR A TIME," "HYDROELECTRIC POWER FLOWED WITH PROMISE." "BUT IN THE SEARCH" "FOR A CLEAN, EFFICIENT, AND ABUNDANT SOURCE OF ENERGY," "ALL THE WORLD'S RIVERS TOGETHER" "WOULD NEVER PROVIDE ENOUGH," "AND BY ITSELF, NEITHER WOULD THE WIND." "BUT ALONG WITH GEOTHERMAL AND SOLAR POWER," "THE WIND PROVIDES CHEAP, DECENTRALIZED ENERGY" "THAT CAN SHARE THE LOAD" "WITH TRADITIONAL, CENTRALIZED GENERATING PLANTS." "TAKING ADVANTAGE OF CURRENT TECHNOLOGY," "THESE WINDMILLS ARE MUCH MORE EFFICIENT" "THAN THEIR DUTCH COUNTERPARTS OF A FEW CENTURIES AGO." "IN ANY CASE, WHETHER ELECTRIC POWER" "COMES FROM THE WIND OR THE WATER," "FROM NUCLEAR POWER OR FROM COAL," "IT'S GENERATED" "USING THE PRINCIPLE OF ELECTROMAGNETIC INDUCTION," "AND THE SAME PRINCIPLE PLAYS A ROLE" "IN ANY CIRCUIT WHERE ELECTRICITY IS USED." "AN ELECTRIC CURRENT IN ANY CIRCUIT" "CREATES A MAGNETIC FIELD WHICH, WHENEVER IT CHANGES," "INDUCES A CURRENT IN THE SAME CIRCUIT" "THAT OPPOSES THE CHANGE." "THIS PHENOMENON IS CALLED SELF-INDUCTION." "THE EFFECT OF SELF-INDUCTION" "IS LARGER IN A COIL OF MANY TURNS," "CALLED A SOLENOID," "PRECISELY BECAUSE IT LOOPS MANY TIMES" "AROUND THE CHANGING FLUX." "THAT'S WHY A SOLENOID IS USED" "AS A SYMBOL OF SELF-INDUCTANCE IN AN ELECTRIC CIRCUIT," "WHERE AN INDUCTOR MAY BE AN ELEMENT" "LIKE A RESISTOR OR CAPACITOR." "CURRENTINCREASING INANINDUCTOR" "CAUSESANOPPOSING ELECTROMOTIVEFORCE" "ACCORDING TOFARADAY'SLAW," "ANDSINCETHEFLUX ISPROPORTIONAL" "TOTHECURRENT THATCREATESIT ," "THATELECTROMOTIVEFORCE ISEQUALTO MINUSACONSTANTL" "TIMESTHERATE OFCHANGEOF CURRENT." "LISCALLEDTHE INDUCTANCE OFTHECIRCUITELEMENT." "ANINDUCTOROPPOSES ANDSLOWSDOWN" "THEBUILD-UPOF CURRENT INA CIRCUIT," "WHILEA RESISTORMAYCAUSE THECURRENTTO DECAY" "BYDISSIPATINGENERGY." "BUT BEYOND SUCH PRACTICAL CONCERNS," "WHAT'S THE VALUE OF MICHAEL FARADAY'S THEORY?" "FOR STARTERS, UNLIKE A MOTOR," "IT'S NOT SIMPLE AND OBVIOUS," "AND UNLIKE ANY MACHINE," "IT'S NOT SOMETHING ONE CAN PUT A PRICE ON." "IN FACT, THE VALUE OF ELECTROMAGNETIC INDUCTION" "IS BEYOND THE ECONOMICS OF TECHNOLOGY." "THAT'S BECAUSE FARADAY'S THEORY REVEALS SOMETHING NEW" "ABOUT THE NATURE OF ELECTRIC AND MAGNETIC FIELDS," "AND, IN THE PROCESS, CHANGES THE RULES" "BY WHICH NATURE'S GAME IS PLAYED." "MAGNETIC FIELDS CIRCULATE BUT NEVER CONVERGE TO A POINT." "ELECTRIC FIELDS CONVERGE TO A POINT" "BUT NEVER CIRCULATE." "IN MATHEMATICAL LANGUAGE," "THAT MEANS THE LINE INTEGRAL" "OF AN ELECTROSTATIC FIELD AROUND ANY CLOSED PATH" "IS ALWAYS EQUAL TO 0." "BUT WHEN THE MAGNETIC FLUX THROUGH A LOOP" "CHANGES WITH TIME," "IT CREATES AN ELECTROMOTIVE FORCE" "AROUND THE LOOP," "AND THAT ELECTROMOTIVE FORCE IS DUE TO AN ELECTRIC FIELD" "WHOSE LINE INTEGRAL IS NOT EQUAL TO 0." "IN OTHER WORDS, THERE IS A WAY" "TO MAKE ELECTRIC FIELDS CIRCULATE AFTER ALL," "AND IT'S ACCOMPLISHED BY CHANGING THE MAGNETIC FLUX." "WHEN FARADAY DISCOVERED THAT A CHANGING MAGNETIC FLUX" "COULD MAKE AN ELECTRIC FIELD CIRCULATE," "HE ADDED SOMETHING EXTRAORDINARY" "TO THE LAWS OF ELECTRICITY AND MAGNETISM." "SO WHILE IT'S OFTEN SAID" "THAT THERE'S NOTHING NEW UNDER THE SUN," "THE SAYING DOESN'T APPLY TO ELECTROMAGNETIC INDUCTION." "I'D LIKE TO SHOW YOU SOMETHING TRULY EXTRAORDINARY," "BUT FIRST, I'LL EXPLAIN WHAT YOU WILL SEE." "WHEN WE FIRST STARTED DISCUSSING ELECTROMAGNETIC INDUCTION," "THIS IS HOW I EXPLAINED HOW IT WOULD WORK." "I SAID THE WIRE MOVES THROUGH THE MAGNETIC FIELD" "AND BECAUSE OF THE MOTION OF THE WIRE," "THE CHARGES INSIDE HAVE A FORCE ON THEM." "THAT SETS THE CURRENT INTO MOTION," "BUT WHEN WE FINALLY FORMULATED FARADAY'S LAW," "WE WERE DESCRIBING IT IN QUITE A DIFFERENT WAY." "THEN WE SAID THE ELECTROMOTIVE FORCE" "IS PROPORTIONAL TO THE RATE OF CHANGE" "OF THE TOTAL MAGNETIC FLUX THROUGH THE CIRCUIT." "THAT SUGGESTS THE EXPERIMENT COULD BE DONE DIFFERENTLY." "WHAT WE COULD DO IS HAVE A SOLENOID." "THAT'S A HELICAL WINDING, LIKE THIS," "IN WHICH THE WIRE GOES AROUND AND AROUND." "IF WE PASS A CURRENT THROUGH THAT," "IT CREATES A MAGNETIC FIELD IN THIS DIRECTION." "IF I HAVE A LOOP OF WIRE AROUND THIS SOLENOID" "AND CONNECTED TO A GALVANOMETER," "WHEN I TURN THE SOLENOID ON," "THE FLUX THROUGH THAT LOOP WILL INCREASE" "EVEN THOUGH THERE'S NEVER ANY MAGNETIC FIELD" "AT THE POSITION OF THE WIRE." "ACCORDING TO FARADAY'S LAW, THE GALVANOMETER SHOULD JUMP." "YOU'LL SAY THE MAGNETIC FIELD AT THE POSITION OF THE WIRE" "IS NOT REALLY 0" "BECAUSE THE MAGNETIC FLUX THAT GOES THROUGH THE SOLENOID" "HAS TO RETURN OUTSIDE," "SO THERE'S SOME MAGNETIC FIELD OUTSIDE." "I CAN CURE THAT PROBLEM BY TAKING THE SOLENOID" "AND MAKING IT BEND AROUND ONTO ITSELF" "INTO A DOUGHNUT OR TOROID." "HERE'S WHAT THE TOROID LOOKS LIKE." "IT HAS SOME WINDINGS OF METAL WIRE AROUND IT," "AND WHEN A CURRENT IS PASSED THROUGH THOSE WINDINGS," "LINES OF MAGNETIC FLUX" "GO AROUND THROUGH THE TOROID" "AND CLOSE ON THEMSELVES WITHOUT EVER GOING OUTSIDE," "SO THE MAGNETIC FLUX OUTSIDE OF A TOROID" "IS REALLY EQUAL TO 0." "NOW, IF I TOOK A LOOP OF WIRE" "AND RAN IT THROUGH THE MIDDLE OF THE DOUGHNUT" "AND THEN BACK AROUND" "AND CLOSED IT ON THE GALVANOMETER," "WHEN I TURN ON THE TOROID," "THE GALVANOMETER SHOULD JUMP" "EVEN THOUGH THE MAGNETIC FIELD" "AT THE POSITION OF THE WIRE" "IS EXACTLY 0." "THAT'S WHAT I WILL SHOW YOU." "I HAVE HERE A TOROID." "WHEN I TURN THE TOROID ON BY MEANS OF THIS SWITCH," "THERE WILL BE MAGNETIC FLUX INSIDE," "BUT THERE WON'T BE ANY MAGNETIC FIELD AT ALL OUTSIDE." "I STILL HAVE MY LOOP OF WIRE CONNECTED TO THE GALVANOMETER." "YOU KNOW IF THERE'S A MAGNETIC FIELD" "TURNED ON AT THIS WIRE, THE GALVANOMETER WILL JUMP." "I CAN PUT THE WIRE ON TOP OF THE TOROID." "I TURN IT ON," "AND THE GALVANOMETER DOESN'T BUDGE." "WHEN I TURN THE SWITCH, ABSOLUTELY NOTHING HAPPENS." "IF I TAKE THIS WIRE AND PUT IT THROUGH THE DOUGHNUT," "THE RESULT IS COMPLETELY DIFFERENT." "I OPEN THE WIRE" "AND THREAD IT THROUGH THE MIDDLE" "AND CLOSE IT AGAIN." "EVEN THOUGH THERE'S NO MAGNETIC FIELD" "AT THE POSITION OF THE WIRE," "WHEN I TURN THE TOROID ON, THE GALVANOMETER WILL JUMP." "WATCH." "THERE IT IS." "WHEN I TURN IT OFF, THE SAME THING HAPPENS." "THAT IS THE ESSENCE OF ELECTROMAGNETIC INDUCTION." "THERE'S SOMETHING ELSE OVER HERE I WANTED TO SHOW YOU." "IT'S THIS PENDULUM." "THIS IS AN ORDINARY PENDULUM," "BUT IT HAS A PIECE OF COPPER AT THE END." "THE COPPER SWINGS BETWEEN THE POLES" "OF AN ELECTROMAGNET." "THE MAGNET'S NOT TURNED ON RIGHT NOW." "IF THE MAGNET WERE TURNED ON," "THE COPPER WOULD SWING INTO THE MAGNETIC FIELD." "THEN BY ELECTROMAGNETIC INDUCTION," "ELECTRIC CURRENTS WOULD BE INDUCED" "TO RUN AROUND IN THE COPPER." "WHENEVER CURRENTS RUN AROUND IN A PIECE OF METAL," "THAT CAUSES HEATING." "ENERGY WOULD BE LOST FROM SOMEWHERE." "WHERE DOES THE ENERGY COME FROM?" "THE ONLY PLACE POSSIBLE" "IS THE SWINGING OF THE PENDULUM." "THE PENDULUM SHOULD SLOW DOWN" "IF I TURN ON THE MAGNET," "WHICH I CAN DO WITH THIS SWITCH." "I'LL GET THE PENDULUM SWINGING AGAIN," "AND YOU GET THE RHYTHM OF THE SWINGING," "AND WHEN I CLOSE THE SWITCH," "YOU CAN DETECT THE PENDULUM SLOWING DOWN." "HERE WE GO." "I'LL GET IT SWINGING AGAIN." "I'M GOING TO CLOSE THE SWITCH RIGHT NOW." "WATCH THIS." "THERE." "DID YOU NOTICE THAT?" "ONE MORE THING I'D LIKE TO SHOW YOU." "NOT ONLY CAN ELECTROMAGNETIC INDUCTION" "STOP A PIECE OF METAL," "IT CAN GET ONE GOING AGAIN." "METAL DOESN'T LIKE A STRONG, CHANGING MAGNETIC FIELD," "WHICH I HAVE RIGHT HERE." "IF I PUT THIS RING OF ALUMINUM" "IN THE FIELD AND TURN IT ON," "THE ALUMINUM JUMPS" "WHEN IT'S TURNED ON." "THERE." "I CAN'T DO BETTER THAN THAT," "SO I'LL SEE YOU NEXT TIME." "CAPTIONING IS MADE POSSIBLE BY THE ANNENBERG/CPB PROJECT" "CAPTIONING PERFORMED BY THE NATIONAL CAPTIONING INSTITUTE, INC." "CAPTIONS COPYRIGHT 1986 CALIFORNIA INSTITUTE OF TECHNOLOGY," "THE CORPORATION FOR COMMUNITY COLLEGE TELEVISION, THE ANNENBERG/CPB PROJECT" "PUBLIC PERFORMANCE OF CAPTIONS PROHIBITED WITHOUT PERMISSION OF NATIONAL CAPTIONING INSTITUTE" "Annenberg Media" "¶" "For information about this and other Annenberg Media programs call 1-800-LEARNER and visit us at"