The Student Room Group

Direction of current

ned help.png

Is this correct?
Thanks!
Original post by Zenarthra
ned help.png

Is this correct?
Thanks!


The LHR and RHR both use conventional (positive) current.
This is always in the opposite direction to the flow of electrons in a wire.

Left Hand Rule.
To work out the direction of the force on a wire when you pass a current through it in a magnetic field. (The so called "motor" rule.)
For the Left Hand Rule the thumb is the direction of the Force.
The pointer (first finger) in the direction of the field. (Into the page/screen in your diagram)
The centre finger is in the direction of the conventional current. Electrons move in the opposite direction.

In your diagram if the electrons are moving down the page as shown, the conventional current is up.
In that case the force will be to the left.
If the conventional current is upwards the force will be to the right as shown.


The Right hand (dynamo) rule is for working out the direction of the induced current when you move a wire in a field.
First decide which situation you are attempting to describe.
(edited 10 years ago)
Reply 2
Original post by Stonebridge
The LHR and RHR both use conventional (positive) current.
This is always in the opposite direction to the flow of electrons in a wire.

Left Hand Rule.
To work out the direction of the force on a wire when you pass a current through it in a magnetic field. (The so called "motor" rule.)
For the Left Hand Rule the thumb is the direction of the Force.
The pointer (first finger) in the direction of the field. (Into the page/screen in your diagram)
The centre finger is in the direction of the conventional current. Electrons move in the opposite direction.

In your diagram if the electrons are moving down the page as shown, the conventional current is up.
In that case the force will be to the left.
If the conventional current is upwards the force will be to the right as shown.


The Right hand (dynamo) rule is for working out the direction of the induced current when you move a wire in a field.
First decide which situation you are attempting to describe.


Oh so, flemings left hand is used for magnetic force experienced by a current carrying wire in a magnetic field? F=BIL

And flemings right hand rule is used for the applied force in order to generate a current around the wire.

Both cases are used for conventional current and the flow of electrons is opposite to the direction of conventional current?
Original post by Zenarthra
Oh so, flemings left hand is used for magnetic force experienced by a current carrying wire in a magnetic field? F=BIL

And flemings right hand rule is used for the applied force in order to generate a current around the wire.

Both cases are used for conventional current and the flow of electrons is opposite to the direction of conventional current?


Yes.
When I was taught this (a long time ago!) we always said Left Hand (Motor) Rule and Right Hand (Dynamo) Rule.
The direction of the current is always conventional (positive) flow. This is always opposite to the flow of electrons.
LH Rule for the force on a wire carrying a current and placed in a magnetic field. Yes. F=BIL
RH Rule for when you induce a current or emf in a wire by moving it in a magnetic field. E=BLv
(edited 10 years ago)
Reply 4
Original post by Stonebridge
Yes.
When I was taught this (a long time ago!) we always said Left Hand (Motor) Rule and Right Hand (Dynamo) Rule.
The direction of the current is always conventional (positive) flow. This is always opposite to the flow of electrons.
LH Rule for the force on a wire carrying a current and placed in a magnetic field. Yes. F=BIL
RH Rule for when you induce a current or emf in a wire by moving it in a magnetic field. E=Bqv


You're getting old xD!
But Thanks!

And i think you meant E=Blv :tongue:
(edited 10 years ago)
Original post by Zenarthra
You're getting old xD!
But Thanks!

And i think you meant E=Blv :tongue:


I certainly did. :wink:
Edited in original post.
Reply 6
you could use Fleming's right hand rule for motors but with electron flow... probably better not to as that's rather confusing.

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