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Flemings lefthandrule

ok i know the rule but sometimes i struggle to apply it. Im quite confused by the direction of the current part. The book says the direction of current is conventional current...how does this tell me what direction it is.

and if the direction is conventional current, does that mean it is always the same direction, and doesnt matter what the context is...or will the direction of conventional current depend on whats going on in the example?

I just have no idea how to decide the direction of the current!!

help please

Reply 1

uberteknik

Original post by newblood

In conventional current terms, current flows from the highest to lowest voltage potential. i.e. from the battery or supply +ve terminal towards the -ve terminal.

The physical definition of a current is the rate of flow of electrons and these physically move through a circuit from the -ve to +ve terminals.

With Flemings LHR, the direction the middle finger points, represents the direction of the current. The conventional current flows in the direction the index finger points which gives the +ve (higher) voltage potential at the knuckle end and the lower voltage potential at the finger tip.

Remember though that this is conventional current. electrons actually flow in the opposite direction which is critical if the question asks about charge build up.

Original post by newblood

.....and if the direction is conventional current, does that mean it is always the same direction, and doesnt matter what the context is...or will the direction of conventional current depend on whats going on in the example?

Yes, the directions of the fingers are critical. You have to orientate your hand so that at two fingers line up with the known information. The unknown variable is given by the third finger.

The LHR is for motors. I use the FBI acronym for Force, magnetic B field and current (I). [thumb (F), index (B), middle (I).]

For a motor, the thumb gives the direction of the force when a current (conventional current direction of the middle finger) is moved through a magnetic flux (direction of index finger points in the direction of the field from North (knuckle end) to South (tip end)).

Once again, line up the two known fingers and the third unknown will be answered.