Question

Torque on a charge carrying loop in a magnetic field?

Answer 1

http://prntscr.com/13zygv

Answer 2

@.Sam.

Answer 3

@nincompoop

Answer 4

start with a drawing...

Answer 5

the current goes counter-clockwise as seen from aboveimagine a uniform B-field...

Answer 6

Circular loop.. would it change anything?

Answer 7

no, the result you get can be most easily derived from a square loop, but holds for all shapes

Answer 8

in our case it's a rectangular loop with sides a and b
assume the current through the wire is I
what is the force on each segment of wire due to the B-field?

Answer 9

alright so.. force on side a is.. in the -k direction.. right?

Answer 10

Idl(cross)B.. -j(cross)-i =-k ?

Answer 11

on b is zero.. and on the right vertical side is in the +k direction..

Answer 12

you can pick a coordinate system as you choose
yes, force on the b sides is zero, and the force on the a segments is what in terms of a ?

Answer 13

let i be out of the board, j be right, and k be up

Answer 14

... at least that's my suggestion, I would avoid the unit vectors if we can

Answer 15

can we do it like i is right in the plane.. j is up in the plane.. and k is up outside the plane?
i'm more comfortable with it..

Answer 16

umm. right hand/left hand rules confuse me.. so i prefer it like this..
And Torque=M(cross)B ?

Answer 17

yes your coordinate system is fne
you will wind up with \[\vec\tau=\vec\mu\times\vec B\]but I thought we wanted to prove that...

Answer 18

umm no.. what would be the answer out of the 4 options?

Answer 19

and how? lol.
i dont wanna get suspended for asking the answer. :P

Answer 20

what is the exact question? it asks you for the formula for torque on a circular current loop in a B-field is all?

Answer 21

I'm sorry. This link got lost..
http://prntscr.com/13zygv

Answer 22

This is the question..

Answer 23

oh, not a current-carrying loop, a charge carrying loop
more interesting

Answer 24

um yeah.

Answer 25

well you should be able to figure out the minimum easily enough, so do that first

Answer 26

um. i am not sure about about it.

Answer 27

If it is actually a charge-carrying loop, then torque is zero, since magnetic fields do not act on fixed charges.

Answer 28

but if the loop is spinning with frequency f then the charges are moving...

Answer 29

Where is the full question, please?

Answer 30

http://prntscr.com/13zygv

Answer 31

This Vincent.

Answer 32

But i guess as its a circular loop so I is always perpendicular to B ( I will act tangentially) so.. 0 all.. am i right?

Answer 33

no.. ignore what i just said.

Answer 34

I don't think soat this moment there will be torque