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Flemings left hand rule HARD QUESTION

https://tavistockcollegescience.wikispaces.com/file/view/FP%26F%20-%20Magnetism%20%26%20Electromag.pdf/229948338/FP%26F%20-%20Magnetism%20%26%20Electromag.pdf
For question 1aii on the above link, how do work out the direction of the force? i tried using flemings left hand rule and it keeps giving me the opposite direction
Original post by haron1
https://tavistockcollegescience.wikispaces.com/file/view/FP%26F%20-%20Magnetism%20%26%20Electromag.pdf/229948338/FP%26F%20-%20Magnetism%20%26%20Electromag.pdf
For question 1aii on the above link, how do work out the direction of the force? i tried using flemings left hand rule and it keeps giving me the opposite direction


Lorentz force is given by
F=q(E+v×B)=qv×B\vec{F}=q(\vec{E}+\vec{v} \times \vec{B}) = q \vec{v} \times \vec{B}
Using the right hand rule the resultant vector from v x B points upwards: F=qvBy \vec{F} = q vB\vec{y} now remember the charge is -e
so F=evBy \vec {F}=-evB\vec{y} which points downwards
Original post by haron1
https://tavistockcollegescience.wikispaces.com/file/view/FP%26F%20-%20Magnetism%20%26%20Electromag.pdf/229948338/FP%26F%20-%20Magnetism%20%26%20Electromag.pdf
For question 1aii on the above link, how do work out the direction of the force? i tried using flemings left hand rule and it keeps giving me the opposite direction

Remember that the direction of conventional current is opposite of the electron flow
Reply 3
Original post by PhysicsMathsTut
Remember that the direction of conventional current is opposite of the electron flow


ok i know that but looking at the question as it is on the paper- the first finger of my left hand is pointing into the paper, my thumb is pointing right and second finger down. Since the 2nd finger points down the conventional current is downwards so the electron feel a force upwards?
Original post by haron1
ok i know that but looking at the question as it is on the paper- the first finger of my left hand is pointing into the paper, my thumb is pointing right and second finger down. Since the 2nd finger points down the conventional current is downwards so the electron feel a force upwards?


Thumb shows the direction of the force on the electrons. Second finger is current, it should point left

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Reply 5
It's Towards Q, use flemming's right hand rule.
(edited 8 years ago)
Reply 6
Original post by PhysicsMathsTut
Thumb shows the direction of the force on the electrons. Second finger is current, it should point left

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why should the second finger point left- the electrons don't flow that way(current)?
Original post by haron1
why should the second finger point left- the electrons don't flow that way(current)?


The electrons flow as a result of the force on them. You're asked about the force. Because of the movement of the plane, each electron is moving right. That's current to the left when you're using Fleming's LHR

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Reply 8
Original post by PhysicsMathsTut
The electrons flow as a result of the force on them. You're asked about the force. Because of the movement of the plane, each electron is moving right. That's current to the left when you're using Fleming's LHR

Posted from TSR Mobile


thanks
the first finger (magnetic field, as shown by the X's and the arrow pointing right) should point right. the thumb (force) is then pointing upwards, the correct answer

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