The Hall Effect

  • Thread starter gokugreene
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If I move a strip of copper mechanically with my hand through a uniform magnetic field will their be a drift velocity? And if so will the drift velocity be in the same direction as the moving copper strip? What would the magnitude of the drift velocity be if this happens? Can you have a drift velocity without a current in the copper strip?

This confusion comes about after reading a my physics book. It says that you can use the Hall Effect to measure the drift velocity of charge carriers.

Thanks!
 

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  • #2
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gokugreene said:
If I move a strip of copper mechanically with my hand through a uniform magnetic field will their be a drift velocity? And if so will the drift velocity be in the same direction as the moving copper strip? What would the magnitude of the drift velocity be if this happens? Can you have a drift velocity without a current in the copper strip?
This confusion comes about after reading a my physics book. It says that you can use the Hall Effect to measure the drift velocity of charge carriers.
Thanks!
A current exists ONLY when there is relative motion between the strip of copper and the magnetic field. The magnitude of the current depends on the relative speed. the faster you move the strip of copper through the B field, the higher the current.
 
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If I move a strip of copper mechanically with my hand through a uniform magnetic field will their be a drift velocity?
Not unless the strip of copper makes a complete circuit.
And if so will the drift velocity be in the same direction as the moving copper strip?
No. This velocity is at right angles with the direction of the field and the movement of your hand in the usual xyz coordinates.
What would the magnitude of the drift velocity be if this happens?
This would depend on the total resistance of the circuit. First you have to work out the generated emf. U=Blv Then the current. I=U/R Then the drift velocity from I=nAve. In the last formula v is the drift velocity and in the first formula v is the speed of your hand.
Can you have a drift velocity without a current in the copper strip?
No
This confusion comes about after reading a my physics book. It says that you can use the Hall Effect to measure the drift velocity of charge carriers.
I think your confusion comes from the fact that you think that in order to generate an emf in a magnetic field you have to move a conductor through the field. That is not the only way to generate an emf. It can also be done by charges of a current (in a stationary strip) set up by an external power supply. If these charges go through a magnetic field they will feel a magnetic force of F=Bev. Now v is the drift velocity.
This force is again under right angles with both direction of v (= opposite I) and direction of the magnetic field. If properly set up you will find that F is in the direction of the width w of the strip. F is a real force but difficult to measure. It is easier to measure the resulting emf U (= Hall voltage) across w with a very sensitive volt meter.
I hope this helps.
 

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