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The diagram shows a solenoid connected to a battery. (the solenoid is an electromagnet).
1) Indicate the direction of the current in the wire by an arrow.
2) Label the S pole of the electromagnet.
3) Briefly explain why a solenoid carrying a.c (alternating current) can be used to demagnetise a magnet.
1) Conventional current goes from positive to negative. It traces the movement of positive charge. Which was what Ben Franklin thought moved! Really, electrons move. Who knew? But negative charge moving right is just like positive charge moving left, I guess. So the current is from higher to lower potential: positive to negative.
2) In a solenoid... Well... I know you had a problem with wire and the mag. field before. So a cross section of a solenoid is like|dw:1397277879201:dw|You can probably see how I applied what we did before with the right hand rule.
So, what's north and what's south? Well, that might be new, I don't know. Just like current goes from high to low, the magnetic field lines go from north to south. So, the field arrows point away from the north.|dw:1397278985195:dw|Why would we say there's a north and a south? Well, the field outside of a solenoid seems like a magnet, so we treat it as such.
3) Demagnetization is fun. Especially for destructive people. You can make it really hot (Curie temperature for the metal), or you can smash it in a different magnetic field or no field at all! Or, you can put it in a stronger or just different magnetic field. And that's what the solenoid can do.
If the current in a solenoid changes, so does the magnetic field. If the magnet to be demagnetized is in a changing field, it might shift back and forth until, on average, all the little magnetic bits of the metal are scattered around.
The magnet was magnetized in the first place because of the little bits being aligned.
Hopefully this helps. Good luck!