Motors and Generators Question (1 Viewer)

[Sp3ctre]

I thought the answer to this question was B but it's C, can anyone explain why?

https://gyazo.com/5462d3cf3ffe5cb9fc4c9e77473aa705


Sorry the bottom got cut out, D is just the reverse of B

 

[jazz519]

So since it is asking for force, we calculate force on a rod using F=BILsintheta

So the two motors both have the same magnetic field strength, length and current flowing through them.

The theta = 90 degrees in both as you can check by visualising the side PQ at different points of its rotation that is always perpendicular to the magnetic field, but the force direction sign just flips because of the use of the commutator changing current direction.

I think you have confused the radial magnetic field use over the normal bar magnet magnetic field in terms of torque, which it provides the constant torque in

So essentially the side PQ always experiences the same force in both motors, but the torque is different due to the angle between the plane of the coil and the magnetic field

 

[Sp3ctre]

So since it is asking for force, we calculate force on a rod using F=BILsintheta

So the two motors both have the same magnetic field strength, length and current flowing through them.

The theta = 90 degrees in both as you can check by visualising the side PQ at different points of its rotation that is always perpendicular to the magnetic field, but the force direction sign just flips because of the use of the commutator changing current direction.

I think you have confused the radial magnetic field use over the normal bar magnet magnetic field in terms of torque, which it provides the constant torque in

So essentially the side PQ always experiences the same force in both motors, but the torque is different due to the angle between the plane of the coil and the magnetic field

Oh yeah that clears it up, I was getting confused with force and torque, thanks!