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Path of Charge in Magnetic Field
Name: Steven
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
a positive charged particle will spiral in one direction
when moving parallel with a uniform magnetic field, and a negative
charged particle will spiral in the opposite direction. But,does a
magnetic field affect the forward direction of charged particles.
e.g would a positive charged particle be "pulled" towards either the
north or south poles of the magnetic field and a negative charged
particle in the opposite direction?
Replies:
Hello Steven,
The influence of a uniform magnetic field on a charged particle
depends upon the initial velocity of the particle relative to the
field. The tendency is for a charge to travel "around" a magnetic field.
If the particle is initially traveling perpendicular to a uniform
magnetic field, then it will travel in an arc tracing out a circle
(over and over again). If the particle is not traveling completely
perpendicular then it will trace out a path that looks like a spring
or slinky (circular when viewed from the top, but steadily going
up). If the particle is traveling initially in a direction
perfectly aligned (or anti-aligned) with the magnetic field, then it
will continue perfectly along that line with no deviation and never
feel any influence from the field.
This is all due to the force a magnetic field exerts on a particle
to depend both upon the direction of the field and the direction of
motion of the particle. The force acts at a right angle to both the
magnetic field and to the velocity. If the field and the velocity
are both colinear, then there is no force!
There are devices called "cyclotrons" that manage to store beams of
charged particles (or ions) in such a fashion for use in scientific
applications and study.
cheers,
Michael S. Pierce
Steven,
A magnetic field can only push or pull an electric charge perpendicular
to itself. For a standard bar magnet, this direction is around the
magnet. A magnetic field is also limited to changing only the direction
of an electric charge. IT cannot cause a charge to speed up or slow
down. A changing magnetic field can produce an electric field to do
this, called induction, but the magnetic field itself cannot. Even in
the case of induction, the electric field forms around the magnetic
field. Even then, the electric charge would not be pulled toward the
magnet's pole.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
First of all: charges spiral when they are moving perpendicular to a
uniform magnetic field. In fact, if the magnetic fields were all
there was to it, the charges would not spiral, but instead move in
unending, unchanging circles. The spiraling is due to slowing by
friction. When a charge moves parallel to a magnetic field, the
field exerts no charge on it.
A static magnetic field does not do any work on a charge it
affects--that is, it can only change its direction. It cannot speed
it up or slow it down. Magnetic north and south poles neither
attract nor repel electric charges. The most they can do is deflect them.
Richard Barrans
Department of Physics and Astronomy
University of Wyoming
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Update: June 2012
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