Direction of current in circuits

Case A: At this very moment a beam of electrons is traveling from the gun in the back or
neck of the CRT directly towards your face (pretend you are looking at Cathode Ray
Tube [CRT] if you have a flat screen monitor). Luckily for you the beam strikes the
phosphorous-coated surface of the CRT prior to striking you. Now make a fist with your
left hand directly in front of your face. Now point your thumb directly in the direction of
your face. Your thumb is now pointing in the same direction as the electron beam. This
electron beam produces a magnetic flux that curls about the beam in the direction of the
fingers on your left hand.



Case B: Next, I want you to imagine that your CRT was actually an ion propulsion
engine, and instead of electrons coming straight at you there were positive ions coming
straight at you. Now make a fist with your right hand directly in front of your face. Now
point your thumb directly in the direction of your face. Your thumb is now pointing in the
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same direction as the positive ion beam. This ion beam produces a magnetic flux that
curls about beam in the direction of the fingers on your right hand. Next, point your
thumbs towards each other. Note that your fingers curl in the same direction. When a
negative ion (or electron) and a positive ion move towards each other, the curl of the
magnetic flux around the negative or positive ion curl in the same direction. The positive
ion moves in the same direction as the electrostatic field vector, E. Conventional current
flow is in the same direction as the field vector E, and hence is in the same direction as
the positive ion or charge carrier. Electrons or negative ion flow is in the opposite
direction of the E vector.
The Right Hand Rule states that when you point your thumb in the direction of the
electrostatic field (E) that is driving the beam, the curl of your fingers indicates the
direction of the Magnetic H field.