# Solenoid question

1. Aug 4, 2011

### weatherlight

Hi, I'm new to the forums, and I'm studying to be an aerospace engineer. I'm still in the start of my program, and I'm not in school till next semester, so this isn't for school.

My question is, whats the effect of interlocking coils that are slightly offset carrying a current in the same direction? Do they interfere with eachother creating a back EMF?

I'm not sure how to attack this problem using the knowledge I have.

2. Aug 4, 2011

### Staff: Mentor

Welcome to the PF.

What is the context of the question? Do you have a picture or figure that you can show us to help us understand the question?

3. Aug 4, 2011

### weatherlight

It's just something I'm curious about.

I don't have any pics, but its like a ven diagram with 4 circles. The circles are the solenoids, they would pass through eachother.

I'm wondering what a DC pulse through such a set up would do.

When I get all done with school, i'm interested in getting into field propulsion. Since I've had a lot of time to sit and think, I wondered what a pulse through intertwined solenoids would do. So far my classes haven't dealt with solenoids that weren't connected linearly in a circuit.

I know solenoids are used to create magnetic fields by passing a changing current through them. Would it be possible to make a system with them where they create a "thrust" (for lack of better term)? Do fields interact with the world in this way?

4. Aug 4, 2011

### Staff: Mentor

There is the concept of "Mutual Inductance", which deals with how much flux from one coil couples through another coil:

http://en.wikipedia.org/wiki/Mutual_inductance#Mutual_inductance

To the extent that some of the flux from your driven solenoid is also coupling through the other solenoids, that will tend to induce a voltage in the other solenoids. If there is a load connected to one or more of them, then the current that flows in the other solenoids will create a back-EMF in the first solenoid.

5. Aug 4, 2011

### weatherlight

What if all of them are wired parallel on the same circuit?

6. Aug 4, 2011

### Staff: Mentor

You don't usually wire inductors in parallel. Why would you do that?

7. Aug 4, 2011

### weatherlight

I'm curious as to what it would do, and if there's any uses to such a set up.

8. Aug 4, 2011

### Staff: Mentor

When you connect the inductors in parallel, that constrains their terminal voltages to be equal. You cannot then drive one of them independently from the others....

9. Aug 4, 2011

### weatherlight

I know. I'm interested on what effect the entire apparatus would have in relation to the surrounding enviroment.

Like would a pulsing field oriented in one direction create a force capable of propelling... well, anything lol. Similar to creating thrust by expelling hot gases in a jet engine.

Last edited: Aug 5, 2011
10. Aug 5, 2011

### cragar

They have rail guns and ring guns that use electromagnetic induction to propel metal objects.

Last edited by a moderator: Sep 25, 2014