G) Generator Principle - Electromagnetic Induction




1831 - Michael Faraday discovered that current and voltage can be induced when a conductor (closed loop) moves within a magnetic field.

Engraving by John Cochran (1821-1865) of a portrait of Michael Faraday
 in his late thirties, painted by Henry Pickersgill (1782 - 1875)
This image (or other media file) is in the public domain
because its copyright has expired.

Induced Current

© Copyright 1997, Sergey Kiselev
and Tanya Yanovsky-Kiselev


© Walter Fendt, May 8, 1998

(Note: 3 dimensional view)

Wire is perpendicular to page 

If this wire is moved up or down (perpendicular to the field), maximum current (and V) will be generated.



Moved left or right (parallel to the field), no current will be generated





Toward which point should the wire be moved to induce the maximum electric potential? (voltage)






Point 1, perpendicular to field





The wire movement determines
 the direction of the current

School Blocks Youtube? Use file below.


This movie is part of the collection: Prelinger Archives
Audio/Visual: silent, b&w

Creative Commons license: Public Domain



How to find the direction of current
 - Third Left Hand Rule



Step 1:  flux lines - Out of N into S

Step 2: 4 fingers follow flux lines

Step 3: Thumb follows movement of wire (Given)

Step 4: Palm shows Push on electrons - The current direction


Ex) If the wire in the picture below is moved upward, which way will the electrons flow?

Into the page OR Out of the page?




Out of Page





Wire moved right,
Direction of induced current?






List 3 factors that determine the amount of current generated when a magnet is moved is moved through closed coil of wire

St. Mary's H.S. YouTube Channel



(V) Induced voltage - also called EMF - Electromotive Force

V  =  Blv


B - Magnetic Field Strength

l - length of conductor (in meters)

v - velocity of conductor moving through the field






Ex) Describe the direction in which the wire could be moved to produce the maximum potential difference across its ends, R and S.




into the page



To the left or right

(perpendicular to field)





Lenz's Law

St. Mary's Physics Youtube Channel

School Blocks Youtube? Use file below.

Lenz's Law - St. Mary's Physics





Lenzís Law - The magnetic field around induced current opposes the wire motion that produced it.

Another way to demonstrate Lenz's Law

Use a magnetic marble (Amazon)
and an aluminum rail (Home Depot)




November 14, 2008

All the left hand rules only work when moving charges are negative.



What do you do when
moving charge is positive?





Right Hand Rule!





1st Left Hand Rule

2nd Left hand Rule

3rd Left Hand Rule

Left Hand Rule Game

Electron in Magnetic Field

Electron in Magnetic Field II












Physics of Credit Cards


Lenz's Law





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Use any material on this site (w/ attribution)