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.

 

[mukundpa]

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

 

[thepatientmental]

Fleming's left hand rule is a useful tool for understanding the relationship between a current-carrying conductor, a magnetic field, and the resulting force. To answer your first question, the direction of the magnetic field acting on a current-carrying conductor can be determined by placing your left hand with the thumb, index finger, and middle finger at right angles to each other. The index finger represents the direction of the magnetic field, the middle finger represents the direction of the current, and the thumb represents the direction of the resulting force. This rule is often used in conjunction with the right-hand rule, which helps determine the direction of the current in a wire.

In regards to your second question, the left-hand rule can be used practically by aligning your hand with the direction of the current and the magnetic field. In your example, with the current in the north direction and the magnetic field in the south-west direction, you would align your hand accordingly. The index finger would point in the south-west direction, the middle finger would point in the north direction, and the thumb would point in the direction of the resulting force. The key is to align your hand with the current and magnetic field, and the direction of the resulting force will be represented by your thumb.

As for why we use the thumb to represent force alone, it is simply a convention that has been established for ease and consistency. The thumb is used because it is the only finger that can move independently from the other two fingers, making it easier to represent the direction of the force.

I hope this helps clarify any confusion you may have about the motor rule. Remember, practice makes perfect, so keep practicing using the left-hand rule and it will become second nature to you. Best of luck!