left hand rule

[JdoubleU]

I understand the left hand rule. This will tell you the direction of the magnetic field around a conductor. So, if this is correct does the magnetic field change directions 60 cycles a second.

 

[peter]

I don't think the left hand rule nor even the right hand rule meansanything to 99% of electricians. It might be of avail to someone designing motors or such. But, for most of us, it's butterscotch.
~Peter

 

[zog]

I understand the left hand rule. This will tell you the direction of the magnetic field around a conductor. So, if this is correct does the magnetic field change directions 60 cycles a second.

Keep in mind the left hand rule is based on electron flow when most people follow the hole flow theory (Current flow from + to -) in which case the right hand rule applies (Neither theories are accurate FWIW). I don;t think the left hand rule has been taught in theory for at least 40 years (iwire?)

In the same sense as the current "flow" going in one direction the magnetic feild also goes in one direction, again neither are accurate. But for certian theory applications it helps with understanding some concepts.

 

[jim dungar]

I don;t think the left hand rule has been taught in theory for at least 40 years (iwire?)

I know it was taught at least 35 yrs ago.:grin:

The left hand rule is part of the theory that is taught for determining how a solenoid will operate. it definitley is more applicable to DC rather tnah AC circuits.

A 60Hz sine wave has 120 zero crossings (change in direction) per second.

 

[dbuckley]

Yes. yes yes yes (the forum gets miffed if you post really short answers!)

 

[Rick Christopherson]

(Neither theories are accurate FWIW).

I don't know why you would suggest the concept (it is not a theory) is not accurate. It is based on the mathematics of magnetism, and is a simple rule to assist in determining direction without delving into the core equations.

As to the original poster's question, yes, the magnetic field does constantly change, and that is why transformers work on AC but not DC.

 

[Rick Christopherson]

The left hand rule is part of the theory that is taught for determining how a solenoid will operate. it definitley is more applicable to DC rather tnah AC circuits.

No, a solenoid doesn't care about the RHR or LHR. The coil will magnetically attract the plunger regardless of the direction of the current, or even if the current is AC or DC. A permanent magnet plunger will be different, but this is not as common. Motors, on the other hand, are very much dependent on the direction of the magnetic field.

 

[hardworkingstiff]

Keep in mind the left hand rule is based on electron flow when most people follow the hole flow theory (Current flow from + to -) in which case the right hand rule applies (Neither theories are accurate FWIW). I don;t think the left hand rule has been taught in theory for at least 40 years (iwire?)

Why is it that "most people" follow the "hole flow theory" instead of electron flow? I've never understood that.

Isn't current flow a measurement of electron movement? If the electron is moving from left to right, the hole is moving from right to left. So most people will say the current is flowing from right to left? I'm hard headed. Just doesn't make sense to me.

 

[zog]

Why is it that "most people" follow the "hole flow theory" instead of electron flow? I've never understood that.

Isn't current flow a measurement of electron movement? If the electron is moving from left to right, the hole is moving from right to left. So most people will say the current is flowing from right to left? I'm hard headed. Just doesn't make sense to me.

Most people have learned that current flows from positive to negative, electrons "flow" from negative to positive. Not sure why theory is taught that way, it just is. + to -.

 

[zog]

I don't know why you would suggest the concept (it is not a theory) is not accurate. It is based on the mathematics of magnetism, and is a simple rule to assist in determining direction without delving into the core equations.

As to the original poster's question, yes, the magnetic field does constantly change, and that is why transformers work on AC but not DC.

I was refering to the theories of electrons (Or holes) "flowing".

 

[zog]

I know it was taught at least 35 yrs ago.:grin:

The left hand rule is part of the theory that is taught for determining how a solenoid will operate. it definitley is more applicable to DC rather tnah AC circuits.

A 60Hz sine wave has 120 zero crossings (change in direction) per second.

I know what the left hand rule is, however all the recent electrical theory books I have read use the right hand rule. All depends on if you are using conventional or electron flow theories.

Attached is a drawing of the RHR for conductors. There are also RHR and LHR for motors/generators, but thats another topic.

 

[nakulak]

http://www.rare-earth-magnets.com/magnet_university/conventional_vs_electron_flow.htm

 

[Pierre C Belarge]

Hey...when I was in apprentice school, we were taught the 'lefthand rule'.
That was more than 25 years ago...I have not used it or thought of it while in the field. I do teach it though, it is in all the theory books that I have.

 

[Nium]

Most people have learned that current flows from positive to negative, electrons "flow" from negative to positive. Not sure why theory is taught that way, it just is. + to -.

Because Ben Franklin had a 50% chance on getting electron flow direction right and he didn't. So it has always been taught "+" to "-" when as you stated electron flow is "-" to "+". Well for fundamental theory it's taught that way.

 

[zog]

Either way works just fine, as long as you don't mix theory.

 

[Rick Christopherson]

Because Ben Franklin had a 50% chance on getting electron flow direction right and he didn't. So it has always been taught "+" to "-" when as you stated electron flow is "-" to "+". Well for fundamental theory it's taught that way.

Actually, Franklin didn't get the flow wrong, he got the polarity of the charge carrier wrong. He assumed the charge carrier to be positive, but we later learned that it was negative (the electron).

 

[charlie b]

I don't think the left hand rule has been taught in theory for at least 40 years

I learned "hole flow," and the right hand rule, in college. Shortly thereafter, I learned "electron flow," and the left hand rule, in the Navy. I think the Navy still teaches electricity in terms of electron flow.

 

[zog]

I learned "hole flow," and the right hand rule, in college. Shortly thereafter, I learned "electron flow," and the left hand rule, in the Navy. I think the Navy still teaches electricity in terms of electron flow.

I learned hole flow in the Navy. They told us to sit on our left hands when taking exams.

 

[mivey]

We were taught positive charge and negative charge flow but generally used the positive charge flow convention.

Left Hand Rule (Motor Action): Direction of force on a wire in a magnetic field. Extend the thumb, forefinger, and 3rd finger of the left hand into mutually perpendicular positions. The Forefinger points in the direction of flux density (F for flux), the 3rd finger in the direction of current, and the thuMb in the direction of force/motion (M for motion).

Right Hand Rule (Generator Action): Direction of generated voltage corresponding to LHR. Extend the thumb, forefinger, and 3rd finger of the right hand into mutually perpendicular positions. The Forefinger points in the direction of flux (F for flux), the 3rd finger in the direction of voltage, and the thuMb in the direction of force/motion (M for motion).

Right Hand Rule (Current & Magnetic Field): If a current-carrying conductor is held in the right hand with the thumb extended, the fingers will point in the direction of the magnetic field if the thumb points in the direction of current flow. Equivalently, if the coil of a transformer is held in the right hand with the fingers pointing in the direction of current, the extended thumb will point in the direction of the magnetic fields.

 

[Smart $]

Either way works just fine, as long as you don't mix theory.

It amazes me that principles of electric are still referred to as theory.