View Full Version : Help with solenoid and electromagnetics


Executor
03-20-03, 06:20 PM
ok im doing a little outside of class work trying to figure out how a theoretical accelorator could be made using a large enough solenoid, but I can't seem to figure out the Force in Newtons created by the solenoid. What i mean is im using the equation for a solenoid to find the strength of the electro magnetic field in the solenoid so how would i find the force in newtons exerted on an object inside the tube of the solenoid.

Fluidity
03-20-03, 06:44 PM
The force can be characterized, but not calculated exactly. Even in a perfecty uniform magnetic field, there will be one exact point where the force is highest, diminishing everywhere else. Tables are used to predict the force of a solenoid, but each design is somewhat unique. The number of windings, space of separation, materials used, diameter of the plunger, length of the bore...all these things effect the actual force of a solenoid, even the power applied...etc.

James R
03-20-03, 09:20 PM
Executor:

<i>ok im doing a little outside of class work trying to figure out how a theoretical accelorator could be made using a large enough solenoid, but I can't seem to figure out the Force in Newtons created by the solenoid.</i>

The force on what?

<i>What i mean is im using the equation for a solenoid to find the strength of the electro magnetic field in the solenoid so how would i find the force in newtons exerted on an object inside the tube of the solenoid.</i>

What kind of object?

Executor
03-20-03, 10:11 PM
an equation that could be used to find the force in Newtons if you know the force of the field in Teslas

James R
03-20-03, 11:02 PM
The magnetic field inside a solenoid is approximately uniform, so it will exert no force on a magnet placed inside unless you ramp the amount of current going through it so as to get a magnetic induction effect. Even then, you'd need the magnet to be launched to stick out of one end of the solenoid.

There is no simple equation for working out the force in this arrangement. You'd need to calculate the rate of change of magnetic flux as the current was ramped, and know the details of the magnetic field of the magnet to be launched.

Hmmm....

Executor
03-21-03, 07:25 PM
The field inside the magnet goes in a direction so as it would push a magnet out one end of the solonoid if it was placed in the opposite end.

Running a magnet through the middle of the solonoid without a current running through the solonoid created a current. therefore if you run a current in the opposite directions of the current created by running the magnet through you will get the reverse effect..... the solonoid puts force on the magnet running through the middle of it opposite of the direction it is being pushed. ie.. stopping perpetual motion.

James R
03-22-03, 06:58 AM
Executor:

<i>uhh... the field is not uniform..</i>

uhh... yes it is. It has constant magnitude inside the solenoid, and points in the same direction everywhere. That's what uniform means.

<i>The field inside the magnet goes in a direction so as it would push a magnet out one end of the solonoid if it was placed in the opposite end.</i>

A magnet half in and half out of one end of the solenoid will experience a force, but one in the middle of the solenoid will have no force on it, provided the solenoid current is constant.