Question

A positively charged disk is spinning in a clockwise direction as seen from above. What is the direction of the magnetic field? PLEASE HELP

Answer 1

isnt there a right hand rule? or rule of thumb? i forget what these things were called

Answer 2

if you think about grabbing it with your hand such that the fingers bend in the spinning direction, your thumb points in the moving direction

Answer 3

Right Hand Rule. Fingers in the direction of Conventional current ("positive charge flow", left hand for electrons). Thumb is in the direction of North pole.

Answer 4

so a spinning disk is your second hand rule right? even though its not a coil of wire or solenoid? @mstoldegon

Answer 5

@amistre64

Answer 6

Sorry. To clarify, you use the "Right Hand Rule" to determine the direction of "North" when a Negative charge (typically electrons) are moving in a circular path. (the rule of thumb is for measuring a distance - not related)
If looking down on the circular movement of a negative charge (electrons in a wire, an excess of electrons on a disk, negative ions spinning around a black hole, etc.) was Counter Clock Wise, the direction of the North pole of the resulting magnetic filed would be up towards you.
Take your Right hand and make a fist but with the thumb pointing up. The direction of the fingers represents the direction of the negative charge or flow. The thumb (pointing up) represents the direction of the North pole of the resulting magnetic field.
The Rule of Thumb allows one to view a rotating electric charge, negative or positive, and determine the the direction of the North pole of the magnetic field. If rotating charge is negative, use the Right Hand for the direction of rotation. If the rotating charge is positive, use the Left Hand for the direction of the rotation. The thumb always points in the direction of the North Pole.
Hope this helps clarify that it is not just electrons, moving through wires in a rotating manner. that produces magnetic fields.

Answer 7

Sorry again - up too late.
Right Hand for the direction of the rotation of Positive charges, Left hand for for the direction of Negative charges.
Thumb still points in the direction of North.
Time for some Zzzzzz's.

Answer 8

Did you figure out that the spinning disk would produce a magnetic field with North pointing away (down) and South pointing towards you ("...as seen from above.")?
You would use the right hand but turn your fist so that the thumb was pointing down. The direction of the positive charges are now in a Clockwise direction and the thumb is pointing down.