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# What is the left hand rule?

Wiki User

2013-09-22 10:14:18

*Note: When we talk about the left hand and right hand rules, we have some confusion built into the ideas. The confusion comes from the "old school" model that said electric current flowed from positive to negative. This is the so-called conventional current picture of electricity. Conventional current flows from positive to negative. It is electron current that flows from negative to positive. And that's what actually happens, and how we see things today. But both ideas as regards current flow are still kicked around. If we use Fleming's rule to work things out, then the current direction indications will have to be "reversed" to understand the mnemonic. Be sure to have an accurate picture of which rule and which method of current flow is being used to explain a given electrical situation!

For a wire, the left hand rule states that if the wire is grasped by wrapping the hand around it with the thumb pointing in the direction of electron flow, the fingers will be In a generator, if we apply the left hand rule (using electron flow instead of conventional current), we can find the direction of (electron) current flow that is induced in the conductor if we know the direction of the movement of the conductor and the direction of the magnetic field. Extend the left hand, and stick out the thumb. Then stick out the index finger in a direction that is an extension of the arm. The tumb will be "up" and the index finger will be "out" at 90 degrees from the thumb. Now stick out the middle finger to form a 90 degree angle with both the thumb and the index finger. Now you have a digit pointing in each of three directions that are mutually 90 degrees apart, each one from the others. Let's apply this mnemonic.

By pointing the thumb in the direction of the movement of the wire, and the index finger in the direction of the magnetic field, the middle finger will be pointing in the direction electrons will be moving as a result of the induced voltage in the conductor. It's just that simple and easy. Remember that both these mnemonics are "opposite" of Fleming's left hand rule, because we chose to speak to electron flow rather than use the idea of conventional current.

Left hand is for motor and right hand for generator.

Fore finger in both the direction of Field. Note "F"

Centre finger is for the current, of course, conventional current. Note down "C"

The Main finger is for the Movement of the conductor. Note "M"

Main is thumb. Middle finger, of course, is taken to be the centre.

Wiki User

2013-09-22 10:14:18
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