Flemings left hand rule question Watch

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TheUnderCOVER
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When I done this I got upwards however the mark scheme says downwards and I just can't figure out how to get this
Can anyone explain please

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SDA
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First finger points in direction of field (North to South)
Second finger points in direction of current
Thumb points in direction of force

Follow this and you can't go wrong.
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TheUnderCOVER
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(Original post by SDA)
First finger points in direction of field (North to South)
Second finger points in direction of current
Thumb points in direction of force

Follow this and you can't go wrong.
I've done this but I keep getting upwards :s
Very confused...


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SDA
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The only way I can think you are getting the wrong answer then is either you are using your right hand or you are pointing your second finger in the wrong direction, point it the opposite way to which the arrow is pointing since when it is going through the magnetic field it is travelling 'away from us'.
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TheUnderCOVER
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(Original post by SDA)
The only way I can think you are getting the wrong answer then is either you are using your right hand or you are pointing your second finger in the wrong direction, point it the opposite way to which the arrow is pointing since when it is going through the magnetic field it is travelling 'away from us'.
Aha nope using my left and yes I get downwards when I point my second finger to the opposite direction of the arrow however I don't understand how your supposed to know to point it in the opposite direction of the arrow shown... Could you explain what you mean by the current travelling away from us, wasn't taught anything about that in school


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SDA
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Sometimes we use 'away from us' or 'towards us' when talking about directions since obviously a drawing is only two dimensional so, in this case by saying the current is moving away from us it is just a way of trying to explain the extra dimension (since left and right is used for the magnetic field and up and down is used for the force).

We know the current moves away from us through the magnet since it moves around the loop like a car going round a track (it always points in the direction it is travelling) so the arrow shows it coming towards us on the right side of the picture, as it turns the corner it is now going right to left, as it then turns the next corner it is travelling away from us, after the next corner it is going left to right and then back onto the point we started where it as again pointing towards us.

It may help in the future to draw the arrows on all the way around the loop to get a picture of what is happening.
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TheUnderCOVER
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(Original post by SDA)
Sometimes we use 'away from us' or 'towards us' when talking about directions since obviously a drawing is only two dimensional so, in this case by saying the current is moving away from us it is just a way of trying to explain the extra dimension (since left and right is used for the magnetic field and up and down is used for the force).

We know the current moves away from us through the magnet since it moves around the loop like a car going round a track (it always points in the direction it is travelling) so the arrow shows it coming towards us on the right side of the picture, as it turns the corner it is now going right to left, as it then turns the next corner it is travelling away from us, after the next corner it is going left to right and then back onto the point we started where it as again pointing towards us.

It may help in the future to draw the arrows on all the way around the loop to get a picture of what is happening.
Oh right I think I understand although now all these questions are popping up in my head, don't wanna annoy you too much by making you explain all this :P but I still need to ask if the arrow is pointing towards us in this picture..how are you suppose to know the direction of current if you get me.. It could be going in any direction as it travels around the wire, how are you suppose to know which direction to use when using Flemings left hand rule?

If any of that made sense to you lol sorry for asking you all this


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SDA
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(Original post by TheUnderCOVER)
if the arrow is pointing towards us in this picture..how are you suppose to know the direction of current if you get me.. It could be going in any direction as it travels around the wire, how are you suppose to know which direction to use when using Flemings left hand rule?
In the picture you would say the arrow is pointing towards you, so the current is flowing towards you since the arrow points in the direction of the current at that point.

If no arrow were to be given, you would know the direction by looking at the battery. Current always flows from the positive side (the longer line of the battery) to the negative side (the shorter side).

Don't worry about asking questions, I want to be able to help you understand
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TheUnderCOVER
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(Original post by SDA)
In the picture you would say the arrow is pointing towards you, so the current is flowing towards you since the arrow points in the direction of the current at that point.

If no arrow were to be given, you would know the direction by looking at the battery. Current always flows from the positive side (the longer line of the battery) to the negative side (the shorter side).

Don't worry about asking questions, I want to be able to help you understand
Much appreciated in the picture as the arrow is pointing towards us, when using Flemings left hand rule in this question, the answer would be upwards right? I understand that current is also kind of flowing away as it goes around the circuit so in that way it would be downwards but I just don't understand how you are meant to know if it's flowing towards or away especially when the arrow is given in this question




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SDA
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Referring to the current as flowing towards or away is just a way of labelling directions on the diagram for our own convenience. Just as you would give directions with reference to North, South, East and West, in this diagram we make reference to upwards, downwards, left, right, towards and away. So we see the arrow is pointing in the direction we define to be towards us and if we draw arrows all the way around the loop, the current in the part of the circuit that passes through the magnetic field will be pointing in the 'away from us' direction.

There is no hidden physics behind why the current is flowing towards or away, it is purely just a way of defining a direction based upon the orientation of the diagram.
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TheUnderCOVER
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(Original post by SDA)
Referring to the current as flowing towards or away is just a way of labelling directions on the diagram for our own convenience. Just as you would give directions with reference to North, South, East and West, in this diagram we make reference to upwards, downwards, left, right, towards and away. So we see the arrow is pointing in the direction we define to be towards us and if we draw arrows all the way around the loop, the current in the part of the circuit that passes through the magnetic field will be pointing in the 'away from us' direction.

There is no hidden physics behind why the current is flowing towards or away, it is purely just a way of defining a direction based upon the orientation of the diagram.
Thanks! You've been a lot of help


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hamsa16
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hi
I'm wondering if it's conventional current or the actual current that we are look at
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Stonebridge
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This is an old thread from 2012 and is now closed.
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