# Left-hand Rule: Unreliable or Misinterpretation?

• anil
In summary, the left-hand rule, also known as Fleming's left hand rule, is a method for determining the force effect of a current and field. Using your left hand, the first finger represents the direction of the magnetic field, the second finger represents the conventional current, and the thumb represents the direction of force. This rule is commonly used in motors and other devices. There is also a right-hand rule, which is an alternative method for representing vector products and is used in the context of magnetic fields generated by moving charges. However, both rules have the same underlying principle and are based on the definition of magnetic field as a vector product of velocity and electric field.

#### anil

Is there some thing really called left-hand rule? I have heard my teacher say it but she is not reliable. I have heard of right hand rule(RHR)? Or is it imporsonation of RHR to go with flow of electron instead of protons

Fleming's left hand rule, for working out the force effect of a current and field. Using your left hand, first finger points at the direction of the field, second finger the conventional current, and thumb gives direction of force. Kinda useful for motors and stuff.

I have books that teach the Left-Hand Rule, and others that teach the Right-Hand Rule.

Isn't this all Ben Franklins fault?

It is a matter of convention, which hand or what kind of screw to use to represent result of vector products. Various texts refer to various hands and screws, but they all agree with each other.

Say, in my high school left hand rule was the one which gives you the direction of Lorents force on moving in magnetic field charge. If the field is enetering your open left palm, and the positive charge is moving in the direction of 4 fingers, then the Lorents magnetic force on the charge is directed along the thumb. Reversing anyone quantity (field direction, or velocity direction, or charge sign) reverses force direction. Right screw rule usually refers to direction of magnetic field generated by moving charge. If a positive charge is moving say from you into this display screen, then the magnetic field it generates is circular field going closckwise around the charge.

Both rules (or their various versions) come from definition of magnetic field being just a vector product of velocity of observer moving by stationary electric field times electric field: B' = [vxE]gamma/c^2 (prime refers to moving system, where observer is. In non-moving system vxE=0xE=0 as you can see, thus no "magnetic term" is generated, B=0 when you are not moving versus electric field or electric charge).

FBI

Orginally posted by FZ+
Fleming's left hand rule, for working out the force effect of a
current and field. Using your left hand, first finger points at the direction of the field, second finger the conventional current, and thumb gives direction of force.

Here is an easy way to remember which finger represents what.
Thumb : F (force)
First finger : B (direction of the magnetic field)
Second finger : I (Current)

## 1. Is the Left-hand Rule unreliable?

No, the Left-hand Rule is not inherently unreliable. It is a commonly used tool in science, particularly in physics, and has been found to be accurate in many situations.

## 2. What is the Left-hand Rule used for?

The Left-hand Rule is used to determine the direction of a magnetic field when a current is flowing through a wire. It can also be used to determine the direction of the force on a current-carrying wire in a magnetic field.

## 3. Are there any limitations to the Left-hand Rule?

Yes, the Left-hand Rule may not be applicable in all situations, particularly when dealing with non-uniform magnetic fields or complex wire configurations. It is also based on the assumption of a uniform magnetic field, which may not always be the case.

## 4. What is the difference between the Left-hand Rule and the Right-hand Rule?

The Left-hand Rule is used for determining the direction of a magnetic field or the force on a current-carrying wire, while the Right-hand Rule is used for determining the direction of a magnetic force on a moving charged particle.

## 5. Why is there confusion surrounding the Left-hand Rule?

There may be confusion surrounding the Left-hand Rule due to its multiple variations and different applications. Additionally, it is possible that some may misinterpret or misuse the rule, leading to incorrect results.