# Questions about Fleming's left hand rule

#### phyphysics

I am quite confused about the motor rule.
I have a few questions concerning the topic:

1. How can I determine the direction of magnetic field acting on a current-carrying conductor?

2. How can I use the left-hand rule practically? Suppose that the current is in the north direction, and the magnetic field points south-west, how can I suppose to use the motor rule to predict the direction of the magnetic force? I can control my fingers to bend that way! What are the secrets behind this rule? Is it a MUST that we use the thumb to represent force alone, but not the other two fingers?

Thanks a lot.

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#### mukundpa

Homework Helper
1. I think you want the direction of magnetic field "due" to creeent.....

for this you can use right hend rule, hold the conductor such that the thumb is in direction of current, then the fingers will give the direction of circular magnetic lines of force.

2. You may take component of mag. field in that direction

Actually the thumb rule is given to know the direction of a vecter which is cross product of two vector quantities. As the cross product is normal the plane containing the two vectors and the normal can be taken on either side of the plane right of left hand rules are giving the correct direction. The rule is daveloped by the experemental observations to give whether vector
C = Vector A x Vector B
or vector C = Vector B x Vector A

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