help needed with direction of torque, Thanks (1 Viewer)

shmitler

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This question is from a HSC test, and I understand the working out for the magnitude of the torque, I dont know why the direction of the torque is into the page. help would be appreciated
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jazz519

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Use the right hand palm rule. On side BC the current is going from B to C or downwards you could say (shown in red)

Remember magnetic field lines begin at north and go to south. So the magnetic field direction goes from right to left (shown in blue)

Now in right hand palm rule, your fingers point in direction of magnetic field so align ur fingers so they follow the blue lines

Your thumb points in direction of current so align it with which way the current is pointing in red

Now you just have to see which way is ur palm facing and you will see it is into the page so that is the torque direction on side BC

Screen Shot 2019-10-06 at 11.24.01 pm.png
 

shmitler

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Thats what i was thinking, but isnt that the direction of the force on the wire, not the torque?. or is it the same thing and im missing something
 

jazz519

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In this case it is the same. That type of scenario it is different, if we are talking about the whole coil. Where BC would be into the page and AD out of the page so the net effect of that is a clockwise torque (but that is only if we talk about the whole coil, which is not asked here)
 

Hscbuzman

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Use the right hand palm rule. On side BC the current is going from B to C or downwards you could say (shown in red)

Remember magnetic field lines begin at north and go to south. So the magnetic field direction goes from right to left (shown in blue)

Now in right hand palm rule, your fingers point in direction of magnetic field so align ur fingers so they follow the blue lines

Your thumb points in direction of current so align it with which way the current is pointing in red

Now you just have to see which way is ur palm facing and you will see it is into the page so that is the torque direction on side BC

View attachment 27261
Correct answer but confusing explanation
 

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