The Student Room Group

slight mag fields confusion

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Hi. I have a couple questions about this. Firstly, using the left hand rule surely the answer would be that the force is 90' to the field (however the correct answer is D). i must be using the wrong rule...

Also another unrelated question, is it correct that the left hand rule is used when a current induces a magnetic field and the right hand rule is used when a magnetic field induces an emf? if so, how is the right hand rule used (which finger represents force, field current? is the the same but on the opposite hand?). I can't find any websites with this info.
(edited 8 months ago)
There is no magnetic field mentioned.
Reply 3
Original post by tarmac-the-cat
There is no magnetic field mentioned.

That explains why I was so confused lol. Thank you for the link :smile:
Reply 4
Do you mean the right-hand grip rule? This tells you the direction of magnetic field caused my a DC current. Thumb points in direction of conventional current, fingers curl in direction of field.
Reply 6
Original post by tarmac-the-cat
Do you mean the right-hand grip rule? This tells you the direction of magnetic field caused my a DC current. Thumb points in direction of conventional current, fingers curl in direction of field.

no that's not what i meant. pretty sure that you can use a similar rule to left hand when a magnetic field induces a current (same force, field, current but on the opposite hand). someone confirmed this to me earlier irl, that it is used when a magnetic field induces a current but maybe that's incorrect
Original post by bertielarter
no that's not what i meant. pretty sure that you can use a similar rule to left hand when a magnetic field induces a current (same force, field, current but on the opposite hand). someone confirmed this to me earlier irl, that it is used when a magnetic field induces a current but maybe that's incorrect


When a current flows through a wire, it creates a magnetic field around the wire. If the wire is also placed in a region of magnetic field, the two magnetic fields interact and cause the wire to move. This is called the motor effect.
The direction of the force relative to the directions of the current and the magnetic field may be predicted using Fleming’s left-hand rule.



Next, when a wire that is part of a circuit is moved across a magnetic field, a voltage is “induced” in the wire, causing a current to flow. This is called the generator effect. The direction of the induced voltage or current in a wire moving through a magnetic field at right angles to the field may be determined using Fleming’s right-hand rule.

Left hand is for motors, right hand for generators

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