Torque and flux question (1 Viewer)

[peeasoup]

Can someone please gimme a good response to a question like this - Explain why the torque on a current loop in a magnetic field is zero when the magnetic flux through the coil is at a max.
I pretty much know it, but cant give a good response and get full marks. So could someone just post a goodish, bout 4 line response ?
thanks.

 

[TripleJ]

Can someone please gimme a good response to a question like this - Explain why the torque on a current loop in a magnetic field is zero when the magnetic flux through the coil is at a max.
I pretty much know it, but cant give a good response and get full marks. So could someone just post a goodish, bout 4 line response ?
thanks.

This question is based on the idea of motor.

Use your right hand rules mate. When the magnetic flux through the coil is at maximum the forces (according to your right hand rule) are cancelling out - the sum of the forces is 0.

 

[Xayma]

The perpendicular distance from the point to the line is 0.

Or due to transmissibilty of forces, the upwards and downwards force cancels out having no net force.

 

[peeasoup]

So i would just talk about that when the flux across the coil is max, the coil is 90 degrees to B. And when the angle is 90, cos90 = 0 (torque = 0). Bu I dont see how you can get 4 marks out of it. And also, is it correct to say that the when the perpendicular distance between the coil and magnetic field is max, the torque is 0. That sounds right doesnt it ?

 

[TripleJ]

So i would just talk about that when the flux across the coil is max, the coil is 90 degrees to B. And when the angle is 90, cos90 = 0 (torque = 0). Bu I dont see how you can get 4 marks out of it. And also, is it correct to say that the when the perpendicular distance between the coil and magnetic field is max, the torque is 0. That sounds right doesnt it ?

Kind of. Remember that the field isn't just a single line (its just represented that way for ease). I wouldn't use the words 'when the perpendicular distance'. I would say that when the maximum flux is passing through the coil that the torque is 0 as the forces [according to my right hand rules] sum to 0 resulting in no torque (m=rf, and f=0).

You can then draw a diagram showing the coil cutting the flux as described and the forces cancelling.

 

[TripleJ]

Normally for 4 marks they expect a diagram.

 

[peeasoup]

yeh. thanks.

 

[TripleJ]

Your welcome.