Linear Accelerator
Most recent answer: 10/22/2007
Q:
I am a student and I am constructing a linear magnetic accelerator (gauss rifle). I need to know the electrostatic charge of steel to be able to complete part of it. I was wondering if you had any books, or ideas as to its charge. Steel is an alloy, and there are a lot of different types that could be made, but I was wondering if there was a certain type of general steel (not stainless steel) that is mass produced (because I am sure that I have that type). Help would be much appreciated.
Thanks,
- John B (age 17)
Urban School of SF
- John B (age 17)
Urban School of SF
A:
John -
Were puzzled about why youre asking about electrostatic charge.
Like other materials, steel is electrically neutral. Isnt it driven
forward by magnetic forces in this gun? We dont know the design
used, but if some of the magnetic force is on currents flowing
through the steel, then the electrical property youre interested in
is the conductivity- how easy it is for that current to flow. A
couple of magnetic properties are also probably relevant, depending
on the design: the magnetic susceptibility (how much a small field
magnetizes the steel) and the saturation magnetization (how magnetic
it gets in a large field). All these properties vary quite a bit
between different steels, as you guessed- stainless, for example, has
particularly weak magnetism and low conductivity. We dont know if some
type of steel is so much more common than others that you could bet
on it being what you have.
We forwarded this to Kevin, a member of our campus
href="http://www.physics.uiuc.edu/groups/physics_society/">Physics
Society who has experience with the project that youre referring
to. Heres what he had to say:
---------------------
What does he mean by the electrostatic charge of steel? By nature,
steels neutral, of course. If hes looking for the maximum charge
that steel can hold before it breaks down or something, theres no
need to worry about that... itll spark before then, Id be more
concerned about him getting shocked. If hes thinking about electron
holes in the material, thats for semi-conductors. Steels got a
conduction band instead, and just holds charge. If hes having
problems with steel melting or something (on the off chance that
thats what hes asking) then he should try working with greater
surface area contacts or smaller currents. On the other hand, if
hes having problems with steel melting, then he shouldnt be doing
it in the first place....
If he isnt working with currents (like a rail gun) but a series of
magnets and using steel projectiles, then hes probably thinking the
dipole moment of the projectile in general when placed in a magnetic
field. That depends mostly on the magnetic field, but if he wants a
textbook, then the book by Purcell has a couple of charts, but I
cant remember exactly if it has steel.... Otherwise, if there are
some material sciences books around, they could probably be found in
those. Hope this helps.
PS, I think he has the wrong terminology... I really dont think he
wants the electrostatic charge for steel... that doesnt make any
sense... you can give it some charge, and then itll be different...
and in the presence of a B-field, the overall charge doesnt change,
it just polarizes domains....
Ask him what hes doing. If hes working with high currents (like
the rail gun) tell him to take precautions and tell him to stay away
from it... If its just a series of magnets and steel balls, tell
him that any potential calculations he would do with the information
hes looking for is probably a very bad guideline to base the actual
project on. Encourage testing and adding only one set of magnets at
a time, etc. Its not quite as deadly as current, but depending on
the magnets hes using and how many he uses, he can potentially hurt
someone.
---------------------
All of us here at the Physics Van agree with Kevin that this project
is a very bad idea. There are a lot of things that can go wrong and
it could be very dangerous, even potentially lethal to try this
without a lot of experience and resources.
-Tamara
Were puzzled about why youre asking about electrostatic charge.
Like other materials, steel is electrically neutral. Isnt it driven
forward by magnetic forces in this gun? We dont know the design
used, but if some of the magnetic force is on currents flowing
through the steel, then the electrical property youre interested in
is the conductivity- how easy it is for that current to flow. A
couple of magnetic properties are also probably relevant, depending
on the design: the magnetic susceptibility (how much a small field
magnetizes the steel) and the saturation magnetization (how magnetic
it gets in a large field). All these properties vary quite a bit
between different steels, as you guessed- stainless, for example, has
particularly weak magnetism and low conductivity. We dont know if some
type of steel is so much more common than others that you could bet
on it being what you have.
We forwarded this to Kevin, a member of our campus
href="http://www.physics.uiuc.edu/groups/physics_society/">Physics
Society who has experience with the project that youre referring
to. Heres what he had to say:
---------------------
What does he mean by the electrostatic charge of steel? By nature,
steels neutral, of course. If hes looking for the maximum charge
that steel can hold before it breaks down or something, theres no
need to worry about that... itll spark before then, Id be more
concerned about him getting shocked. If hes thinking about electron
holes in the material, thats for semi-conductors. Steels got a
conduction band instead, and just holds charge. If hes having
problems with steel melting or something (on the off chance that
thats what hes asking) then he should try working with greater
surface area contacts or smaller currents. On the other hand, if
hes having problems with steel melting, then he shouldnt be doing
it in the first place....
If he isnt working with currents (like a rail gun) but a series of
magnets and using steel projectiles, then hes probably thinking the
dipole moment of the projectile in general when placed in a magnetic
field. That depends mostly on the magnetic field, but if he wants a
textbook, then the book by Purcell has a couple of charts, but I
cant remember exactly if it has steel.... Otherwise, if there are
some material sciences books around, they could probably be found in
those. Hope this helps.
PS, I think he has the wrong terminology... I really dont think he
wants the electrostatic charge for steel... that doesnt make any
sense... you can give it some charge, and then itll be different...
and in the presence of a B-field, the overall charge doesnt change,
it just polarizes domains....
Ask him what hes doing. If hes working with high currents (like
the rail gun) tell him to take precautions and tell him to stay away
from it... If its just a series of magnets and steel balls, tell
him that any potential calculations he would do with the information
hes looking for is probably a very bad guideline to base the actual
project on. Encourage testing and adding only one set of magnets at
a time, etc. Its not quite as deadly as current, but depending on
the magnets hes using and how many he uses, he can potentially hurt
someone.
---------------------
All of us here at the Physics Van agree with Kevin that this project
is a very bad idea. There are a lot of things that can go wrong and
it could be very dangerous, even potentially lethal to try this
without a lot of experience and resources.
-Tamara
(published on 10/22/2007)