# Electric field on a Hall ProbeWatch

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#1
http://i57.tinypic.com/2ev7voh.png

There is an electric field due to the Hall Effect, but the mark scheme says it is going upwards?

However, i deduced that i was going downwards due to:
Current flows right, B-field is into Plane, thus due to Fleming's LHR, the magnetic force acts UPWARDS on the electrons.
Therefore the electric force must act downwards to act against the magnetic force because of the build up of electrons?

0
5 years ago
#2
(Original post by minnigayuen)
http://i57.tinypic.com/2ev7voh.png

There is an electric field due to the Hall Effect, but the mark scheme says it is going upwards?

However, i deduced that i was going downwards due to:
Current flows right, B-field is into Plane, thus due to Fleming's LHR, the magnetic force acts UPWARDS on the electrons.
Therefore the electric force must act downwards to act against the magnetic force because of the build up of electrons?

Here are the steps in the reasoning

- conventional current flows to the right
- field into page
- force on positive charges is upwards
- positive charge moves to the top of the slice
- and so the top of the slice becomes positively charged (if the charge carriers are positive)

What does the question actually ask you to find?
You are using terms like electric force/magnetic force/going upwards etc which are not clear.
You haven't posted the actual question.
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#3
(Original post by Stonebridge)
Here are the steps in the reasoning

- conventional current flows to the right
- field into page
- force on positive charges is upwards
- positive charge moves to the top of the slice
- and so the top of the slice becomes positively charged

What does the question actually ask you to find?
You are using terms like electric force/magnetic force/going upwards etc which are not clear.
You haven't posted the actual question.
But won't the force which is upwards be on the electrons? That's how i learned it, so that the top face will be negatively charged.

Here's the full question - it's the very last part:

http://i57.tinypic.com/sxg5jb.png
0
5 years ago
#4
(Original post by minnigayuen)
But won't the force which is upwards be on the electrons? That's how i learned it, so that the top face will be negatively charged.

Here's the full question - it's the very last part:

http://i57.tinypic.com/sxg5jb.png
Well it certainly helps to have the actual question.
Yes there are two electric fields.
There is one that pushes electrons to the left and conventional positive charge to the right. So this one is left to right. This creates the current flow through the slice.
For positive charge carriers.
Then we have the positive charge on the top of the slice resulting from the magnetic force. This results in a concentration of positive charge at the top and an electric field pointing from top to bottom of the slice. The top is positive and the bottom is negative. This is the internal field inside the slice. It's this field that creates the equilibrium in the slice that stops more upwards or downwards movement of charge and resists the magnetic force pushing upwards.
For negative charge carriers, the opposite is true.
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#5
(Original post by Stonebridge)
Well it certainly helps to have the actual question.
Yes there are two electric fields.
There is one that pushes electrons to the left and conventional positive charge to the right. So this one is left to right. This creates the current flow through the slice.
Then we have the positive charge on the top of the slice resulting from the magnetic force. This results in a concentration of positive charge at the top and an electric field pointing from top to bottom of the slice. The top is positive and the bottom is negative. This is the internal field inside the slice. It's this field that creates the equilibrium in the slice that stops more upwards or downwards movement of charge and resists the magnetic force pushing upwards.
You haven't posted the actual mark scheme so I can't comment on what, exactly, it says. But in my experience, mark schemes can be very confusing for students. They are written for the examiner. Not the student.
Why is it that the positive charges are pushed upwards? I thought that in Flemings LHR, the components are the direction of the conventional current, and the magnetic force on the electrons.

And the mark scheme is literally just the arrow EH pointing up, and the arrow EC pointing right.

Plus can you also help me out on my "Binding Energies" thread please? Thanks
0
5 years ago
#6
Right, I think I have the source of confusion. It's partly my fault for not checking this, but part of the question is missing and I didn't look at this closely enough. My fault.
Here we go again.

In a Hall slice it depends on whether the charge carriers are positive or negative. (They are often positive/semiconductor)
If the field is into the page, and conventional current is to the right, as in the diagram, the force on the charge carriers is upwards.
If the charge carriers are electrons, the top becomes negative. If the charge carriers are positive, the top become positive.
In the question the carriers are, I presume, electrons.
Sorry for the confusion.
I've modified my earlier reply so as not to confuse others reading this from the start.
0
#7
(Original post by Stonebridge)
Right, I think I have the source of confusion. It's partly my fault for not checking this, but part of the question is missing and I didn't look at this closely enough. My fault.
Here we go again.

In a Hall slice it depends on whether the charge carriers are positive or negative. (They are often positive/semiconductor)
If the field is into the page, and conventional current is to the right, as in the diagram, the force on the charge carriers is upwards.
If the charge carriers are electrons, the top becomes negative. If the charge carriers are positive, the top become positive.
In the question the carriers are, I presume, electrons.
Sorry for the confusion.
I've modified my earlier reply so as not to confuse others reading this from the start.
Okay thanks a lot! So why does the Electric Field direction due to the Hall Effect act upwards? I thought that if the top face is negative, due to the negative charge carriers, then the Electric Field would act downwards (because of the build up of negative charge repelling any more electrons) in order to oppose the Magnetic field.
0
5 years ago
#8
(Original post by minnigayuen)
Okay thanks a lot! So why does the Electric Field direction due to the Hall Effect act upwards? I thought that if the top face is negative, due to the negative charge carriers, then the Electric Field would act downwards (because of the build up of negative charge repelling any more electrons) in order to oppose the Magnetic field.
The Hall effect produces a negative charge at the top of the slice if the negative charge carriers are pushed upwards. There is a corresponding lack of negative (positive) charge at the bottom. This creates a field that pushes positive charge upwards. They are repelled by the excess positive charge at the bottom. Electric field is defined as the direction of the force on positive charge. This field they are talking about is the one created by the movement and distribution of the electrons. Not the field causing the movement upwards of electrons. That is the magnetic field.
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