# Fleming's Left Hand Rule --- URGENT! GCSE TOMORROW!!!!

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#1
Can someone please explain to me how to work out which way the current is flowing in a diagram! Like, if it's going anticlockwise do we point the current finger towards us or the other way?

And also, what is the right hand rule by the way?? Is the same as the left hand rule but to work out the current on our right hands??
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6 years ago
#2
(Original post by nerdygeek101)
Can someone please explain to me how to work out which way the current is flowing in a diagram! Like, if it's going anticlockwise do we point the current finger towards us or the other way?

And also, what is the right hand rule by the way?? Is the same as the left hand rule but to work out the current on our right hands??
The left hand motor rule is used for an induced force (for example, due to a charge carrier cutting through a magnetic field). The first finger points in the direction of the magnetic field (north to south pole) and the second finger points in the direction of conventional current flow (positive to negative.) The thumb should then give the direction of the force.

The right hand dynamo rule is used to work out the direction of an induced current due to the change in magnetic field strength near a conductor. It follows the same conventions as the left hand rule, the second finger represents conventional current flow. I doubt there will be a question about this in GCSE though.

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#3
(Original post by AlphaNick)
Ignore right hand rule for now, just concentrate on the left hand rule.

If you're given a question which asks "what direction will movement be" and you've been given the current and magnetic field direction, you use it to work out the direction of movement.

So you just work out by holding your hand out accordingly.
eg if the field direction is straight up and the current direction is left to right, the movement will be directly towards you.

Okay but in a diagram of a circuit, they tell us which way the current flows right? So how do we know which way to point the current? When you say left to right' do you mean anticlockwise??
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6 years ago
#4
(Original post by nerdygeek101)
Can someone please explain to me how to work out which way the current is flowing in a diagram! Like, if it's going anticlockwise do we point the current finger towards us or the other way?

And also, what is the right hand rule by the way?? Is the same as the left hand rule but to work out the current on our right hands??
To remember: First finger is for (magnetic) Field, SeCond finger is for Current and thuMb is for Motion
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6 years ago
#5
This never works for me. For example, there is a question on a simple electric motor and the current is flowing in an anti-clockwise direction and you are asked to find the direction the motor will spin (it's motion).

If I point the current finger forward on the right side of the motor as I look at it the motion finger points upwards. If I point the current finger back towards myself for the left side of the motor as I look at it the motion is still upwards, and both sides can't move upwards: one has to move downwards.

please can someone explain what I am doing wrong.
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6 years ago
#6
(Original post by Connorbwfc)
This never works for me. For example, there is a question on a simple electric motor and the current is flowing in an anti-clockwise direction and you are asked to find the direction the motor will spin (it's motion).

If I point the current finger forward on the right side of the motor as I look at it the motion finger points upwards. If I point the current finger back towards myself for the left side of the motor as I look at it the motion is still upwards, and both sides can't move upwards: one has to move downwards.

please can someone explain what I am doing wrong.
The direction of force will always be reversed on the opposite side, as the current is flowing in the opposite direction.

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6 years ago
#7
Pl
(Original post by Arithmeticae)
The direction of force will always be reversed on the opposite side, as the current is flowing in the opposite direction.

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Please see my image to see what I mean.
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6 years ago
#8
(Original post by Connorbwfc)
Pl

Please see my image to see what I mean.

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6 years ago
#9
(Original post by Arithmeticae)

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Doesn't matter. I think I understand what you were trying to say. Thanks
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#10
(Original post by AlphaNick)
Key points to remember:
- current flows from positive to negative (terminals on a cell)
- magnetic field flows from north to south

from here you will be able to work out the directions
Okay! Sorry one more question, in circuits, in the drawings of cells, which side is positive and which side negative terminal, like is the longer side the negative terminal or vice versa?
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