Back emf
Definition
Back electromotive force (back emf) is the voltage generated by an electric motor or generator that opposes the applied voltage. It is a consequence of electromagnetic induction and acts to limit the current in the circuit.
5 Must Know Facts For Your Next Test
- Back emf is proportional to the speed of the rotating machinery.
- The presence of back emf reduces the net voltage across the motor or generator's windings.
- In a DC motor, back emf increases with rotor speed until it nearly balances the applied voltage at maximum speed.
- Back emf plays a critical role in protecting electrical components from excessive currents by providing natural feedback control.
- The mathematical expression for back emf in a motor is $E_{back} = k \cdot \phi \cdot \omega$, where $k$ is a constant, $\phi$ is magnetic flux, and $\omega$ is angular velocity.
Review Questions
- How does back emf affect the current in an electric motor?
- What factors determine the magnitude of back emf in a generator?
- Why is back emf important for protecting electrical components?
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Related terms
Faraday's Law of Induction: States that a change in magnetic flux through a coil induces an electromotive force (emf) in the coil.
Lenz's Law: Indicates that induced current flows in such a direction as to oppose the change in magnetic flux that produced it.
Electric Generator: A device that converts mechanical energy into electrical energy by electromagnetic induction.
