Electricity and Magnetism : AC - DC Generators / A Series/Parallel Circuit Puzzle / Circle of Magnetism / Dynamo 1/ Dynamo 2 / Induced Currents - Eddy Currents / Lenz's Law / The Magnetic Field - Lines of Force / The Rotating Copper Disk / Pepsi Can / Helmholtz Coils / Electrons Beam
Induced Currents - Eddy Currents

This exhibits shows that an electrical current is induced in a conductor material when it is exposed to a changing magnetic field. 

DO

TURN THE MAGNET ON BY PRESSING THE RED BUTTON. CONNECT THE COIL TO THE METER  ON THE RIGHT, MOVE THE COIL BETWEEN THE  POLES OF THE MAGNET.

SEE

THE METER SHOWS A CURRENT IS INDUCED IN THE COIL; WHENEVER A CONDUCTING WIRE MOVES IN A MAGNETIC FIELD, SO AS TO CUT     ACROSS THE LINES OF FORCE, THE ELECTRONS IN THE CONDUCTOR    EXPERIENCE A FORCE , THIS CAUSES   A CURRENT TO FLOW IF THERE IS A CLOSED CIRCUIT.

DO

MOVE THE SOLID PIECE OF ALUMINUM BETWEEN THE POLES OF THE        MAGNET.

FEEL

THE RESISTANCE TO THE MOTION.

WHAT IS HAPPENING?

THE INDUCED CURRENT CIRCULATES INSIDE THE METAL FORMING AN EDDY CURRENT. THE INTERACTION OF THIS CURRENT WITH THE MAGNETIC FIELD GENERATES A FORCE WHICH WILL TEND TO IMPEDE THE MOTION (LENZ ‘S LAW).

DO

MOVE THE SLOTTED PIECE OF ALUMINUM BETWEEN THE POLES OF           THE MAGNET.

FEEL

THERE IS LESS RESISTANCE TO THE MOTION

WHAT IS HAPPENING?

WHEN THE ALUMINUM IS CUT INTO STRIPS THERE IS LESS OPPORTUNITY FOR THE EDDY CURRENTS TO FORM A LARGE LOOP IN THE MATERIAL. THE INDUCED CURRENTS ARE GREATLY REDUCED, AND SO IS THE IMPEDING FORCE

IN THE REAL WORLD

THE ARMATURE OF TRANSFORMERS ARE LAMINATED, I.E. MADE UP OF THIN INSULATED LAYERS PERPENDICULAR TO THE MAGNETIC FIELD IN ORDER TO PREVENT THE FORMATION OF EDDY CURRENTS THAT WOULD GENERATE HEAT AND WASTE ENERGY