Torque and Force... (1 Viewer)

[cutemouse]

Hello,

I am very confused... Textbook says that maximum torque is obtained when a loop (or loops..) of current carrying wire are parallel to the magnetic field, and that When the plane of loops is at right angles to the magnetic field, it would experience zero torque.

But when a current carrying wire is in line with magnetic field, it experiences no force. And of course it experiences maximum force when it's perpendicular to magnetic field.

I'm so confused. Could someone please explain this to me?

Thanks

 

[3unitz]

for those that care,

the torque on a rectangular coil consisting of N loops is given by:

T = NIABcos@

here we have a cos@ factor, not a sin@ like we do in the force formula (you should be able to derive this equation). the magnetic field exerts a force on the vertical sections of wire, not the horizontal sections. when the plane is parallel to the magnetic field, cos@ = 1, hence a maximum torque.

if you know a little bit of vector notation, the torque formula is given more precisely by T = NIA x B
the direction of A is perpendicular to the plane of the coil, hence a maximum when the plane of the coil is parallel to the B field (A and B will then be perpendicular).