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# Physics electric fields watch

1. (Original post by crana)
so do you reckon itis sort of the same as:

"The coil is linked to the flux"

"The coil has the potential to be cut by the flux (like when the magnet moves in and out of the coil/magnetic field grows and shrinks, is what i mean by potential)"
Yeah, only then can you induce emf with a coil and a magnet. Cripes, ouch, my brain's hurting now
2. (Original post by crana)
ok
thanks
np
3. (Original post by jonas123)
but how do you know they are repelling?

do you not have to use one of the 'hand' rules to work out the direction of current?
sure you can work it out that way but I just know that repelling = opp. directions and attracting = same direction. We did it as an example in class (and I just did the same exam question andI was right on the markscheme)
4. (Original post by jonas123)
i'm not THAT lazy :P

thx for the notes crana and everyone else...

another question, it was on a past paper. There are 2 long wires xcm apart. The current in wire 1 is moving up and the force on wire 2 is to the right (so two long wires, wire 1 on the left, wire 2 on the right). The current in wire 1 is I and the current in wire 2 is 2I.

Which way is the current in wire 2 going? (ie up or down)

Which way is the force on wire 1acting? (ie left or right)

What is the ratio of the force on wire 1 and wire 2? (wire1:wire2)
is this june 2002 for edexcel?
if so current in wire 2 is down
force of wire 1 is tho the left
ratio is 1:1
5. i don't get how you work out the direction of the current, the first question was work out the direction of it. i could guess it but i'm not sure how.

don't you need to use the left hand rule or something?
6. oh ok thx. yup spec i think it was that paper, the direction is down though. how is the ratio 1:1?
7. (Original post by jonas123)
i don't get how you work out the direction of the current, the first question was work out the direction of it. i could guess it but i'm not sure how.

don't you need to use the left hand rule or something?
first you need to know the field direction for each wire, if you roll the fingers of your right hand and point your thumb in the direction of the current, so in this case for wire 1 thumb upwards, fingeres in an anticlockwise direction this give you the field.
Then use left hand rule to find the current, field is going into the page, force is given in the question if you are on the same question as me and thus the current must be downwards
8. (Original post by jonas123)
oh ok thx. yup spec i think it was that paper, the direction is down though. how is the ratio 1:1?
the ratio is 1:1 because of the old for every force X exerted on object B by object A, object B exerts a force equal in magnitude but opposite in direction to X on A.
9. (Original post by jonas123)
oh ok thx. yup spec i think it was that paper, the direction is down though. how is the ratio 1:1?
newton's 3rd law i think
10. oh yeh that crazy rule lol...

the problem with the corkscrew rule spec is, that on one side of the wire, the field goes into the page, and the other side, the field comes out of the page...

is it right to say that the field is in opposite directions either side of the wire?
11. (Original post by jonas123)
oh yeh that crazy rule lol...

the problem with the corkscrew rule spec is, that on one side of the wire, the field goes into the page, and the other side, the field comes out of the page...

is it right to say that the field is in opposite directions either side of the wire?
yes but you only consider the field next to wire 2
12. oooooooooooooooooooooohhhhhhhhhh hhhhhhhhhhhhhhhhh!!!

it all makes sense now lol!
13. (Original post by jonas123)
oooooooooooooooooooooohhhhhhhhhh hhhhhhhhhhhhhhhhh!!!

it all makes sense now lol!
good
14. (Original post by Speciez99)
first you need to know the field direction for each wire, if you roll the fingers of your right hand and point your thumb in the direction of the current, so in this case for wire 1 thumb upwards, fingeres in an anticlockwise direction this give you the field.
How is that anticlockwise? Only if you look down on your thumb, that's against the current isn't it? If you look up on it in the direction of the current it's actually clockwise...
15. (Original post by mik1a)
How is that anticlockwise? Only if you look down on your thumb, that's against the current isn't it? If you look up on it in the direction of the current it's actually clockwise...
On right hand its anti clockwise, going from your knuckles to your finger tips on your right hand is anticlockwise for me if the thumb is pointing up.
16. (Original post by Speciez99)
On right hand its anti clockwise, going from your knuckles to your finger tips on your right hand is anticlockwise for me if the thumb is pointing up.
maybe it is true for his right hand

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