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So I was studying my physics notes. They are on the magnetic field shown by a straight current carrying wire. To demonstrate that theres the oersted's experiment. The starting goes like this-

Insert a thick copper wire between 2 points, X and Y, in a circuit. The wire should be perpendicular to the plane of paper. Place a compass horizontally to the wire. Switch on the current. The compass needle shows deflection

My question is - what does placing the wire XY perpendicular to the plane of paper mean?

And why would you do that? Please help.

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  • $\begingroup$ Why do you think it should be otherwise? $\endgroup$
    – user36790
    Oct 2 '16 at 6:29
  • $\begingroup$ first of all, I don't even understand what paper we are talking about. If you have studied this experiment then can you please explain me which paper we are talking about? $\endgroup$ Oct 2 '16 at 6:44
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“The paper” is probably just meaning the table. So let's put the wire vertically going in the up-down direction. Using the right-hand-rule we obtain that the magnetic field will be circles in the plane of the table/paper.

The compass will align itself to the magnetic field lines. Therefore the rotating compass should be positioned such that it points towards the wire or parallel to it. When you turn on the magnetic field, it can align itself with the magnetic field lines.

Take a look at some video of the experiment. There you can see that the magnet will align itself perpendicular to the wire and parallel to the plane that the wire is perpendicular to (that sentence is probably unnecessarily complex).

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  • $\begingroup$ and my teacher also told me something like, the force is more when you align the magnetic field perpendicular to the direction of electric current flow $\endgroup$ Oct 4 '16 at 6:33
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My question is - what does placing the wire XY perpendicular to the plane of paper mean?

It means you poke the wire through the paper. If you were to shake some iron filings on to the paper they'd line up along the magnetic field lines like little compass needles. The magnetic field lines can be drawn like this:

enter image description here

By the way, despite what you might be told by people who can't answer your questions, there are people who understand magnetism and how it works. Don't listen to people who tell you physics can't supply the answers. It can. That's why we do physics. We do physics to understand the world, not to make predictions. Don't forget that Maxwell wrote On Physical Lines of Force. The force is real, and so are those iron filings and the pretty patterns:

enter image description here

Whilst there are no "lines of force" per se in the space around the wire, they do map out something real - a magnetic field. Electromagnetic field interactions result in linear and rotational forces. A uniform magnetic field is a place where the linear forces cancel, but the rotational forces do not. Hence when you throw an electron through the middle of a solenoid, it follows a helical path. Note though that a typical magnetic field is not uniform, and so we see linear forces too. Hence two wires like the above attract one another. But if you reverse the current in one of the wires, they repel.

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  • $\begingroup$ so, if we don't place the wire perpendicular...will the force be less? $\endgroup$ Oct 10 '16 at 6:30
  • $\begingroup$ Not really, because it's only perpendicular to your piece of paper. The force on a charged particle depends on how you throw it. Check out hyperphysics. I think it's a great website. $\endgroup$ Oct 10 '16 at 7:18
  • $\begingroup$ oh ok thanks for the answer!! Also, about the physics answers "why" thing...there are somethings taught in school that when I learn I have a LOT of doubts about..but all these doubts are out-of-course and I understand the basic concept of what is being taught. Will these doubts clear as I go to collage and stuff? $\endgroup$ Oct 10 '16 at 8:17
  • $\begingroup$ I'm sure a lot will. But not all of them. And to be honest, that's a good thing. That's what drives scientists into searching for better understanding. $\endgroup$ Oct 10 '16 at 18:11

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