AS Physics - electromagnetism

This one hefty piece of homework. These are the last ones i'm stuck on.

46) The armature coil of an electric motor has 100 turns and is of length 0.12m/ The coil spins between the poles of a u-shaped magnet, where the magnetic flux density is 0.18T. The magnetic field is uniform.

- Discuss how the force on each side of the coil changes during one complete rotation of the coil.
- Explain why the force acting on each side of the coil has its maximum turning effect when the plane of the coil is parallel to the lines of force of the magnetic field.

These questions are so wordy! Can someone help?

Reply 1

habosh

for A,the force in a magnetic field=BIlsin theta
where I is the current and l is the length and b is the magnetic field strength theta is the angle between the side of the coil and the magnetic field lines,as theta increases the force increases
when the the plane is parallel the current in perpindicular to the magnetic lines,so sin theta=1 so force is maximum

Reply 2

Christophicus

Here is the diagram.
Can someone tell me if this is right?

electro.JPG6.5KB

Reply 3

idiopathic

Widowmaker

Here is the diagram.
Can someone tell me if this is right?

What are the 2 curly arrows showing?

Reply 4

Christophicus

endeavour

What are the 2 arrows showing?

I'm not sure. Probably the direction the coil is supposed to rotate.

Reply 5

habosh

imagine it like this
now anow the coil of n turns carrying a current I when placed in a the Mf shown the two sides will experience a force of NBIL in opposite directions but the coil will experience a couple of BIL a sin gamma .,now when it's plane gamma =90 sin 90=1 which is maximum