MadSci Network: Physics

Re: Why the magnetic field is directly proportional to velocity in an electron?

Date: Thu Jul 5 15:31:52 2001
Posted By: Lawrence Skarin, Faculty, Electrical Engineering, Monroe Community College
Area of science: Physics
ID: 991170363.Ph

Juan, I am disappointed to tell you that this is a fundamental truth 
discovered by experiment.  Danish physicist Hans Christian Oerstad is 
credited with discovering the field direction.  (See Isaac Asimov:  The 
New Intelligent Man's Guide to Science.)  Oerstad observed the field makes 
circles around the charge -- the circle plane being perpendicular to the 
velocity vector.

The easiest way to make moving charges is to pass an electric current 
through a wire.  In 1819, French physicists Biot and Savart experimentally 
derived the law bearing their name relating the magnetic field strength 
outside a thin current-carrying wire to the current in the wire and the 
distance from the wire.  No current -- no magnetic field.  (See almost any 
physics text covering magnetodynamics with the Biot-Savart law in the 

At that time, recognize we hadn't yet discovered the electron!  That 
discovery did not come until the 1890's.  We now know electric current in 
a wire is moving electrons.  (How does it feel knowing something Benjamin 
Franklin didn't know?)

So summing up, it's because experimenters found both to be so.  

Larry Skarin

Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2001. All rights reserved.