Simple Motor Question (1 Viewer)

[gfcardinio]

Hello all,

I need help with this Physics question that showed up in the Trial.

As shown, since the angle of the coil with the magnetic lines is 40° I thought the force on the wire AB would be less than maximum. The marking criteria also says to include the sin 40° but according to my teacher it should be sin 90°. I know why it is so - the wire is still perpencicular to the lines of magnetic flux when drawing a diagram as I had attempted in the far right of the image.

So what is the right answer and why?

(To the best of my knowledge, the security period on this paper has finished)

 

[SpiralFlex]

90 degrees. The best way to visualise this is to consider the top view. You will see as it rotates, it will be always perpendicular to the magnetic field even though the plane of the coil is inclined 40 degrees.

 

[Sindivyn]

You could claim that your 9's look like 4's, and you typed it into the calculator wrong, but yeah, it's 90 degrees as spiral said.

 

[someth1ng]

It is 90 degrees, the torque not be 90 degrees. There is a difference.

 

[SpiralFlex]

You could claim that your 9's look like 4's, and you typed it into the calculator wrong, but yeah, it's 90 degrees as spiral said.

Haha

 

[gfcardinio]

So if they said to calculate torque on the coil, I would enter cos 40°? Could somebody explain this, compared to finding force on the wire?

 

[Sindivyn]

So if they said to calculate torque on the coil, I would enter cos 40°? Could somebody explain this, compared to finding force on the wire?

Yeah, to calculate the torque on the coil you use the angle between the magnetic field and the PLANE of the coil (in this case; 40 degrees). As a result, torque is constantly changing.

To calculate force, however, you use the angle between the CURRENT and the magnetic field (in motors/generators this is always 90 degrees). As a result, force is constantly constant.