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Name: Steven
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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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