The Right Hand Rule, Magnetic Fields & Magnetic Force on Charged Particles
Magnetic Fields from magnets and electromagnets:
Magnetic (B) field lines are lines of magnetic force. Any magnetic material put in proximity to another magnet will magnetically polarize to align along the field lines. Outside a magnet the magnetic field lines go from the north pole to the south pole of a magnet. Inside the magnet, the lines run from south to north.
Finding the direction of B-Fields:
Using the RHR for defining the direction of a B-field around a current carrying wire:
Put your thumb in the direction of the current in the wire. Imagine your thumb as the wire. Wrap your fingers naturally around your thumb. Your fingers point in the direction of the field. Remember, the field revolves around the wire forming a cylinder in space. The farther you go radially from the wire, the weaker the field.
For an electromagnet (solenoid):
You must visualize the B-field inside the coil. If you can find the direction of the B-field inside the magnet, apply the rules above to identify the poles of the magnet.
Finding the direction of a magnetic FORCE:
Using the RHR to define the direction of force on a single charged particle or on a current carrying wire in an external B-field:
When calculating the force on a wire, you may ignore the B-field created by the current in the wire itself. This B-field does not effect the wire that creates it.
Make an L between your index finger and thumb. Keep your hand flat. Put your thumb in the direction of current (or the velocity of the moving charge). Place your fingers straight in the direction of the B-field. The direction of force is straight out of the palm of your hand. (In first year physics you may assume the particles or current is positive charge by nature, i.e., conventional current. A negative charge will deflect in the opposite direction—i.e., the back of your hand). If your hand deviates from an L shape between your thumb and index finger, you may assume at this level that there is no force.
Calculating the magnitude of the magnetic force on a charged particle or current carrying wire:
F = qvB Technically F=qvBsinq, but we will only be working problems at this level with a right angle between the v and B vectors.
(force) = (charge) x (velocity) x (magnetic field intensity)
F = iLB Technically F=iLBsinq, same comment as above
(force) = (current) x (length of wire) x (magnetic field intensity)