Here are the key principles of how an electric motor works:
- Electromagnetism – Electric motors operate based on the principles of electromagnetism. When a current flows through a wire wrapped around an iron core, it creates a magnetic field. This is the basis for how electric motors are able to generate motion from electrical energy.
- Coils and magnets – Electric motors have coils of wire that are energized by an electrical current. These coils are arranged in a fixed position relative to one or more permanent magnets. When current flows through the coils, it creates an electromagnetic field that interacts with the magnetic field from the permanent magnets.
- Lorentz force – According to the Lorentz force law, a moving electric charge in a magnetic field experiences a force perpendicular to both the magnetic field and the charge’s motion. Electric motors utilize this phenomenon by having current-carrying coils placed in a magnetic field. The Lorentz forces cause the coil to rotate or turn.
- Back EMF – As the coil begins to rotate in the magnetic field, it induces its own voltage that opposes the voltage applied to drive the motor. This is called back electromotive force (EMF). Conservation of energy principles require that this back EMF matches the input voltage for continuous steady rotation.
- Torque – The interaction between the coil’s magnetic field and the field from the permanent magnets produces a rotational force or torque that causes the shaft or output of the motor to spin. This provides a mechanical output from the electrical input.
How is the back electromotive force (EMF) generated in an electric motor?
Back EMF is generated in an electric motor through electromagnetic induction. Here’s a more detailed explanation:
- In an electric motor, coils of wire are placed in a stationary magnetic field, usually produced by permanent magnets.
- When electrical current flows through the coils, it creates its own magnetic field based on the right-hand rule. This magnetic field then interacts with the stationary field from the magnets.
- Due to the Lorentz force law, the opposing magnetic fields cause a force on the coils, making them rotate. As the coils spin, they move through the magnetic flux lines.
- This relative motion between the magnetic fields and coils is what generates back EMF through electromagnetic induction. Specifically:
- As defined by Faraday’s law of induction, a changing magnetic flux through a coil will induce an electromotive force (EMF) in the coil.
- As the coils rotate in the motor, they cut across the magnetic flux from the stationary magnets. This changing flux induces an EMF in the coils.
- The direction of this induced back EMF opposes the original incoming power supply, as described by Lenz’s law. It essentially generates its own self-slowing voltage.
- At steady-state operation, the back EMF exactly equals the supply voltage, allowing the motor to run at a constant rotational speed.