currents and stuff q (1 Viewer)

[lilkatie]

okies
q: if a bar magnet is dropped north pole first through a conducting loop of wire a current will be induced in the wire
What is the direction of the current when the magnet approaches and when it falls below the loop

I don't get it =( I don't know how to work it out Lenz's law is giving me a headache....I can't use lenz's law to find teh direction of a current that would be induced either
sure is great that my exam is tomorrow lol
thanks

 

[BlackJack]

Oaky, this is what you need:
Right hand screw rule ready. Current = fingers, B = thumb today.

First look at the bar magnet as it falls towards the coil. (draw a diagram if needed)
B field lines proceed from the magnet downward, through the coil. The strength of this increases, because the tip of the magnet is approaching the coil, and the tip of the magnet is strongest.
-> Lenz's laws says the coil wants to counter that. To decrease the strength of the field going down, it projects a field up, towards the magnet. Screw rule -> field is counterclockwise (we're looking downwards onto the coil)

---
The magnet now passes the coil and is out the other side. You still have B fields going down, into the south pole this time. The south pole is receding from the manget, so the field is getting weaker at the coil.
Again -> Lenz's law says to counter that. It wants to increase the downward current. So screw rule -> clockwise current (we're still looking downwards on the coil).

Is that, in any way comprehensible? Always stop and draw diagram; ask yourself what is happening and proceed step by step.

 

[lilkatie]

hmm i think that helps well i mean it does
but now i just have to apply it to other stuff
thanx hey

 

[zenger69]

u do a distinction course in physics?

Don't you have to be like a super know it all to do Cosmology.

 

[velox]

what are you implying ?