Motor effect physics alevel
I am not sure why the mark scheme for this question says that the force is 0N.
I thought that F = BILSinθ
However, with a coil there are two lengths of wire. Is the force double BILsinθ or do the forces oppose each other an cancel to 0N. If so how does a motor even work as surely a motor has a coil inside it like this. I would greatly appreciate some explanation thanks!
https://ibb.co/cCkxay
I thought that F = BILSinθ
However, with a coil there are two lengths of wire. Is the force double BILsinθ or do the forces oppose each other an cancel to 0N. If so how does a motor even work as surely a motor has a coil inside it like this. I would greatly appreciate some explanation thanks!
https://ibb.co/cCkxay
Original post by splitter2017
I am not sure why the mark scheme for this question says that the force is 0N.
I thought that F = BILSinθ
However, with a coil there are two lengths of wire. Is the force double BILsinθ or do the forces oppose each other an cancel to 0N. If so how does a motor even work as surely a motor has a coil inside it like this. I would greatly appreciate some explanation thanks!
https://ibb.co/cCkxay
I thought that F = BILSinθ
However, with a coil there are two lengths of wire. Is the force double BILsinθ or do the forces oppose each other an cancel to 0N. If so how does a motor even work as surely a motor has a coil inside it like this. I would greatly appreciate some explanation thanks!
https://ibb.co/cCkxay
The force for the current going in one direction and for the other direction oppose each other and balance to 0.
Original post by Cerdic
The force for the current going in one direction and for the other direction oppose each other and balance to 0.
Ok, but when there is a motor the same is true so why does the force not cancel out to 0N ?
Original post by splitter2017
I am not sure why the mark scheme for this question says that the force is 0N.
I thought that F = BILSinθ
However, with a coil there are two lengths of wire. Is the force double BILsinθ or do the forces oppose each other an cancel to 0N. If so how does a motor even work as surely a motor has a coil inside it like this. I would greatly appreciate some explanation thanks!
https://ibb.co/cCkxay
I thought that F = BILSinθ
However, with a coil there are two lengths of wire. Is the force double BILsinθ or do the forces oppose each other an cancel to 0N. If so how does a motor even work as surely a motor has a coil inside it like this. I would greatly appreciate some explanation thanks!
https://ibb.co/cCkxay
Isn’t it a loop and not a coil?
And for a loop, the equation depends on the area F = BAN
I’m not really sure tho
Original post by G.Y
Isn’t it a loop and not a coil?
And for a loop, the equation depends on the area F = BAN
I’m not really sure tho
And for a loop, the equation depends on the area F = BAN
I’m not really sure tho
No because Flux lux linkage = number of turns of wire ´ magnetic field strength ´ area
NΦ = BAN(costheta) NOT F=BAN
I don't see what the difference between a loop and a coil is. Why can a motor have a couple like the one shown int he diagram without the forces cancelling but the loop has forces which cancel??
Original post by splitter2017
Ok, but when there is a motor the same is true so why does the force not cancel out to 0N ?
Because that rotation is on a different plane, and would have the loop rotating about its length, but not rotating in the x-y plane the question is asking for.
Original post by splitter2017
No because Flux lux linkage = number of turns of wire ´ magnetic field strength ´ area
NΦ = BAN(costheta) NOT F=BAN
I don't see what the difference between a loop and a coil is. Why can a motor have a couple like the one shown int he diagram without the forces cancelling but the loop has forces which cancel??
NΦ = BAN(costheta) NOT F=BAN
I don't see what the difference between a loop and a coil is. Why can a motor have a couple like the one shown int he diagram without the forces cancelling but the loop has forces which cancel??
A loop and the couple in a motor are not the same thing, a loop is literally in the shape of a circle
Original post by Cerdic
Because that rotation is on a different plane, and would have the loop rotating about its length, but not rotating in the x-y plane the question is asking for.
Ok I think I get that
Original post by G.Y
A loop and the couple in a motor are not the same thing, a loop is literally in the shape of a circle
A coil is made of more than one loop. Plane of loop refers a particular plane in that one particular loop of the coil. Plane of coil refers to any plane belonging to any one loop in the coil. A coil can be rectangular or take any shape of the structure that is coiled around
And I have made a motor in class with one "loop" and it did work. My loop would have started horizontal to the field so the equal and opposite forces on each wire create a couple. I think the issue was due to the plane at which the loop was relative to the field, not the difference between a loop and a coil. Thanks Cerdic.
(edited 5 years ago)
Original post by splitter2017
Ok, but when there is a motor the same is true so why does the force not cancel out to 0N ?
Something to note is that the net force is zero but the net torque is NON-ZERO.
The loop can rotate because the net torque is not zero.
Original post by Eimmanuel
Something to note is that the net force is zero but the net torque is NON-ZERO.
The loop can rotate because the net torque is not zero.
The loop can rotate because the net torque is not zero.
Torque must be zero when the force is zero because torque is force x distance.
The torque wouldn't be zero in a different plane, but the question is assuming the distance between the wires is negligible.
Original post by Cerdic
Torque must be zero when the force is zero because torque is force x distance.
The torque wouldn't be zero in a different plane, but the question is assuming the distance between the wires is negligible.
The torque wouldn't be zero in a different plane, but the question is assuming the distance between the wires is negligible.
I am not answering the original question. Please see what am I quoting.
Net force is zero does not always imply net torque is zero. You can check up on what is a couple.
http://web.mit.edu/4.441/1_lectures/1_lecture12/1_lecture12.html
I'm guessing the question is why doesn't up and down force cancel out, hence motor stops moving?
We recently did a practical on this and theoretically, it should stop rotating when the coil is at the half way line, however motors are designed with a gap in between them (the split ring commutator in this case). what it means is that as it goes to half way mark, the momentum of the coil allows it to continue rotation through the gap, and as the opposite sides are now attached to the split ring commutator the current continues flowing the same way as in the diagram, hence the motor keeps spinning. The commutator effectively acts like source of Alternating Current.
It's alot easier to explain with a whiteboard or something but I hope it helps!
We recently did a practical on this and theoretically, it should stop rotating when the coil is at the half way line, however motors are designed with a gap in between them (the split ring commutator in this case). what it means is that as it goes to half way mark, the momentum of the coil allows it to continue rotation through the gap, and as the opposite sides are now attached to the split ring commutator the current continues flowing the same way as in the diagram, hence the motor keeps spinning. The commutator effectively acts like source of Alternating Current.
It's alot easier to explain with a whiteboard or something but I hope it helps!
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