Particle Behaviour

**gonegahgah** · Nov3-09, 05:53 PM

When an electron is sent passed a magnetic pole, why is the electron attracted to a place 90 degrees to its motion of travel and 90 degrees to the direction of the magnetic force causing it to deflect towards the 90 degrees to both (ie the 3rd axis)?
Why is it not attracted to the direction of the magnet?

I know the electron effects a magnetic field while it moves relative but wouldn't the attraction logically still be in the direct direction? Why isn't it?

Also, if an electron is just placed above a magnetic pole so that it has no horizontal movement what will it do then?

**Bob S** · Nov3-09, 06:31 PM

The force on a moving electron with a velocity v in a magnetic field B is given by the Lorentz force law:

F = q(E + V x B)

where v x B is a vector cross product. The force is perpendicular to the plane of v and B.

Bob S

**gonegahgah** · Nov3-09, 07:16 PM

That sounds like it would be right. Thx Bob.
Why is it so though?
What happens to the stationary electron which doesn't combine to form a plane?

**Bob S** · Nov3-09, 07:18 PM

Originally Posted by gonegahgah

That sounds like it would be right. Thx Bob.
Why is it so though?
What happens to the stationary electron which doesn't combine to form a plane?

There is no force on a stationary electron by a magnetic field.
Bob S

**jtbell** · Nov3-09, 09:23 PM

Originally Posted by gonegahgah

What happens to the stationary electron which doesn't combine to form a plane?

Huh?

**gonegahgah** · Nov3-09, 09:45 PM

lol, sounds like I'm talking aeroplane electrons...

kool. The electron remains suspended except for gravity and other particle interaction I would guess. That gets me wondering how they accelerate an electron if when stationary it is non-responsive to magnetic fields; I just suddenly realise? I'm not contradicting; just realising that there must be something else you could hopefully clarify for me.

Still curious also how the electron deviates towards the third axis that is perpendicular to both its path and the source of the force rather then towards or away from the source of the force?

**Bob S** · Nov3-09, 11:48 PM

Originally Posted by gonegahgah

That gets me wondering how they accelerate an electron if when stationary it is non-responsive to magnetic fields; I just suddenly realise? I'm not contradicting; just realising that there must be something else you could hopefully clarify for me.?

The Faraday Law of induction produces an E field around a loop through which the magnetic field is changing. Betatrons use this to get over 300 miilion electron volts. See
http://en.wikipedia.org/wiki/Betatron

Still curious also how the electron deviates towards the third axis that is perpendicular to both its path and the source of the force rather then towards or away from the source of the force?

The derivation of the Lorentz force is not straight forward. See
http://galileo.phys.virginia.edu/cla...neticField.htm
Another way is to do a Lorentz transform from a reference frame where the electron is at rest.

Bob S

**gonegahgah** · Nov4-09, 12:11 AM

So for the first one they keep cycling a magnetic field?
Does this generate a secondary electric field of its own in the chamber or does it just effect the injected electrons making them the electric field?

Cool. The math says what is measured to happen doesn't it? Is there theory on the mechanics (the why)?

**Bob S** · Nov4-09, 11:16 AM

Originally Posted by gonegahgah

So for the first one they keep cycling a magnetic field?
Does this generate a secondary electric field of its own in the chamber or does it just effect the injected electrons making them the electric field?

Review theory of betatron. The electrons are constantly being accelerated by the Faraday induction field as long as dB/dt > 0. Electrons radiate (synchrotoron radiation), so they are constantly radiating (losing) energy.

Cool. The math says what is measured to happen doesn't it? Is there theory on the mechanics (the why)?

The math behind the Lorentz force is firm, but not easy. In fact, Faraday first demonstrated the Lorentz force over 150 years ago. See
http://www.sparkmuseum.com/MOTORS.HTM
Bob S

**Bob_for_short** · Nov4-09, 11:22 AM

Originally Posted by gonegahgah

...Why is it so though?...

The form of magnetic field action is an experimental fact. It is a nature feature. Our equations, if we are clever enough, take this fact into account.

**gonegahgah** · Nov4-09, 06:13 PM

For the electron to be induced doesn't it have to be attracted to a magnetic force in the first place whether it is stationary or not?

**Bob S** · Nov4-09, 08:04 PM

Originally Posted by gonegahgah

For the electron to be induced doesn't it have to be attracted to a magnetic force in the first place whether it is stationary or not?

A static magnetic field will not attract an electron. A static magnetic field cannot accelerate an electron.

Bob S

**gonegahgah** · Nov4-09, 08:40 PM

Bob, I agree that a static magnetic field will not accelerate an electron.
But doesn't there have to be some static attraction so for that the movement of the magnetic field to cause the immediate electrons to follow it?
Isn't it just in a state of balanced attraction while stationary?

**Phrak** · Nov4-09, 08:44 PM

You asked in a physics folder called "Classical Physics", but this very odd behavior, where things happening in perpendicular directions, disappears with the Dirac equation.

The electron is treated as a wave whos phase is subject to what is called the electromagnetic potential.

**gonegahgah** · Nov6-09, 04:50 AM

If you have an apple on a table then the table prevents the apple from reaching the ground but the apple has weight so it is still trying to get to the ground.
So an attraction is still there.

**Bob S** · Nov6-09, 02:36 PM

Originally Posted by gonegahgah

Bob, I agree that a static magnetic field will not accelerate an electron.
But doesn't there have to be some static attraction so for that the movement of the magnetic field to cause the immediate electrons to follow it?
Isn't it just in a state of balanced attraction while stationary?

A stationary electron is not attracted by a magnetic field. A moving electron will be deflected (but not attracted) by a magnetic field, in a direction perpendicular to its velocity. This is the way the horizontal deflection circuit (flyback coil) works in many cathode ray tube (CRT) television tubes.