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September 18, 2019

Generator Effect and Motor Effect – underlying Physics principle

Generator Effect and Motor Effect – introduction

Generator Effect and Motor Effect – Fleming’s left hand rule and right hand rule are the 2 key guidelines to discuss generator and motor effects.

The Left hand rule tells us about the direction of force on the current carrying conductor due to the influence of a magnetic field at right angle. This is related to the motor effect.

And on the other hand, the right hand rule tells us about the direction of induced current through a conductor which is moving in a magnetic field at right angle. This rule relates to the Generator effect.

In this post we will discuss the underlying principle of these two effects, their differences and the Physics behind these effects.

read Fleming’s rules

Motor Effect and Generator Effect: underlying principle

If we compare the physics behind the motor and generator operation, then we will see that the underlying principle for both is the same.

This principle can be stated like this: moving electrons experience a force that is mutually perpendicular to both their velocity and the magnetic field they are travelling through.

Motor Effect – Motor Principle

For motor, current flow in the magnetic field causes a deflecting force on the electrons, which in turn causes the deflection of the wire.

Now, how does this deflection of the current carrying conductor happen? I have explained that at the last section of this tutorial.

Motion as a result of current in a magnetic field is called the motor effect.

Here electrical energy is converted to mechanical energy.

Generator Effect – Generator Principle

And in case of generators, the law of induction works.
Here current is produced because of the motion of a conductor in the magnetic field. This is called the generator effect.

Here mechanical energy is transformed to electrical energy.

 Motor effect and Generator effect using Fleming’s rules and their differences

Motor effect: Follows Fleming’s Left Hand Rule

motor effect and generator effect
Figure A

When charge moves along the wire (fig A above, configuration 1), there is a perpendicular upward force on the charge. Since there is no conducting path the force on the charge tugs the wire upward.

In the same figure see the bottom one, (fig A, configuration 2), where the direction of the current flow is reversed. This time the perpendicular force tugs the wire downward.

All the directions here follow the left hand rule of Fleming.

Generator effect: Follows Fleming’s Right Hand Rule

motor effect and generator effect
Figure B

In the figure above, a wire with no initial current is moved downward (obviously along with the charges entrapped in the conductor) in a magnetic field.

As a result the charge in the wire experiences a deflecting force perpendicular to its motion.

There is a conducting path in this direction, so the charge moves along the wire itself, constituting a current through the wire itself.

Now if the movement of the wire (with no current) is made in the opposite direction, i.e. upward here, then the direction of the deflecting force on the charges will also reverse.

This results in a current in the opposite direction through the wire.

All the directions here follow the right hand rule of Fleming.

Effect of Magnetic force on Current carrying wires (explaining deflection of Motor effect)

motor effect and generator effect
Figure C
motor effect and generator effect
Figure D

Logically we can say that if a single charged particle moving through a magnetic field experiences a deflecting force, then a current of charged particles moving through a magnetic field also experiences a deflecting force.

If the particles are a part of a wire when they respond to the deflecting force, the wire also get pushed and deflected (Figure C).

If we reverse the direction of the current, the deflecting force acts in the opposite direction,(Figure D) perpendicular to both field lines and current.

It is a sideways force. This deflecting force is strongest when the current is perpendicular to the magnetic field lines.

Book: Conceptual physics by Paul G. Hewitt
Suggested Post: Electric Charge   

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