Fleming's left hand rule and current ?!?!

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sonic23
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Ok. So i understand which finger and thumb points where and what it is.

But the current: What is current? What is it the flow of? Which direction of current/electron flow does the rule refer to?

agggh this is really annoying me so i would treasure a clear , thorough epxlanation.

thanks anyone
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Cartesian_
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It is conventional current. Electrons flow oppostie the the direction that your second finger points.
Current is the rate of flow of charge I=Q/t

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SSshrinky
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Current is the flow of electrons

It's conventional current- i.e. movement of positrons (so actual current is the oposite direction to this...)


So.. if you have a current flowing through a wire, and it is placed in a magnetic field, it will move because of Flemming's left hand rule.

I don't think I've really explained that very well... Sorry.
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Cartesian_
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It's conventional current- i.e. movement of positrons (so actual current is the oposite direction to this...)
I don't think conventional is that somehow. Conventional current isn't the flow of positrons as positrons don't flow. It was an error made by physicists that is too embarressing to retract completly.
Just remember that whenever current is metioned they are talking about + to -, electron flow [true current] is from - to +
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sonic23
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(Original post by Cartesian_)
I don't think conventional is that somehow. Conventional current isn't the flow of positrons as positrons don't flow. It was an error made by physicists that is too embarressing to retract completly.
Just remember that whenever current is metioned they are talking about + to -, electron flow [true current] is from - to +

So flemings left hand rule refers to convential current flow( from positive to negative;because they though the charged particles were positive).

But the actuall flow of electrons, negative to positive, is opposite to this?
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teachercol
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Exactly
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sonic23
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(Original post by teachercol)
Exactly
******* physics
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Cartesian_
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******* physics
You don't need to worry about any of that really. Just remember current is + to - and that whenever current is mentioned, that is what it is referring to.
You should be able to fingure out elctron flow as electrons are -ev and they would be attracted ot the +ve side fo the battery
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sonic23
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(Original post by Cartesian_)
You don't need to worry about any of that really. Just remember current is + to - and that whenever current is mentioned, that is what it is referring to.
You should be able to fingure out elctron flow as electrons are -ev and they would be attracted ot the +ve side fo the battery
See this question:
Image

I apply flemings left hand rule, with the current as conventional, and i still get the force to be downwards but in the mark scheme it says its upwards.
i dont understand why
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teachercol
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The force on the magnet is opposite to the force on the aluminium rod.
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sonic23
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(Original post by milesofsea)
Prepare to look like a ****** in the exam when you do it :rofl:
lol the invigilators probably get really confused why there are a load of kids sticking their fingers into the paper
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sonic23
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(Original post by teachercol)
The force on the magnet is opposite to the force on the aluminium rod.

But the bodys arent in contact. I forgot, does newtons third law apply to bodys which arent in contact?

Is it because the magnetic field of the magnet exerts an upwards force on the rod, so by N3, the rod exerts an equal but downwards force on the magnet!!!??
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Zig
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(Original post by Cartesian_)
I don't think conventional is that somehow. Conventional current isn't the flow of positrons as positrons don't flow. It was an error made by physicists that is too embarressing to retract completly.
Just remember that whenever current is metioned they are talking about + to -, electron flow [true current] is from - to +
This always screws me over, because I always use true current. Ergh. I hate Physicists of the past making it so god damn annoying for us now lol.
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sonic23
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(Original post by Zig)
This always screws me over, because I always use true current. Ergh. I hate Physicists of the past making it so god damn annoying for us now lol.

so when you use the left hand rule and the conventional current, what direction force do you get on the rod?
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sonic23
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(Original post by teachercol)
The force on the magnet is opposite to the force on the aluminium rod.

I think im mainly confused with the direction of the current. If there is a cell such as that in the below circuit:
Image
does the conventional current go around from the positive plate to the negative plate, or straight through the cell?
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Cartesian_
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I think im mainly confused with the direction of the current. If there is a cell such as that in the below circuit:

does the conventional current go around from the positive plate to the negative plate, or straight through the cell?
It just flows around the circuit from +ve to -ve terminal
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teachercol
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er both

it flows clockwise in your diagram from + to - then through the cell.
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teachercol
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(Original post by Zig)
This always screws me over, because I always use true current. Ergh. I hate Physicists of the past making it so god damn annoying for us now lol.
Thats not really true of course. Its pretty reasonable to define a positive current as being in the direction that positives move.
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Cartesian_
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Thats not really true of course. Its pretty reasonable to define a positive current as being in the direction that positives move.
No it isn't =S
The definition of current is the rate of flow of charge. How in a circuit is any other charge flowing other than the flow of electrons?
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teachercol
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Because currents can flow in all kinds of materials. Some have positive charges, some have negative charges, some have both.

Plasmas, semiconductors, electrolytes ...

You can have currents through things other than metals!
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