2024 - L2 - Motor principle - Presentation

The Motor Principle

  • Electromagnetism discovered by Oersted led to development of electromagnetic motors.

  • Michael Faraday created an electromagnetic motor in 1821.

  • Motor Principle: A current-carrying conductor cutting an external magnetic field experiences a force.

    • This force is perpendicular to the magnetic field and direction of electron flow.

    • Magnitude of force depends on:

      • Strength of the magnetic field.

      • Current magnitude in the conductor.

      • Angle between the conductor and magnetic field.

Important Observations

  • The force (F) on the conductor is perpendicular to both magnetic field (B) and current (I).

  • Reversing current direction or magnetic field reverses the force direction.

Left-Hand Rule for Motor Principle

  • Use left hand to determine direction:

    • Fingers: direction of external magnetic field (B).

    • Thumb: direction of electron flow (I).

    • Palm: direction of force on conductor.

Factors Affecting Force Magnitude

  • Force (F) is proportional to:

    • B: strength of magnetic field.

    • L: length of the conductor in the field.

    • I: current through conductor.

    • sin(θ): angle between magnetic field and current direction.

  • Formula: F = B x I x L x sin(θ).

Magnetic Actions in a Simplified Electric Motor

  • Diagrams show:

    • Magnetic field of the magnet.

    • Magnetic field of the wire.

    • Direction of force on the wire.

    • Electron flow direction through the wire.

Construction of an Electric Motor

  • Coils attached to a split copper ring (commutator) that rotates.

  • Two stationary carbon pieces (brushes) maintain contact:

    • Brushes connected to a battery providing electrons to the coil.

  • Electron flow through motor:

    • From top brush into commutator segment A and coils, exiting through segment B and the bottom brush.

  • Left-Hand Rule applies:

    • End A becomes N-pole, repelled by N-pole of field magnet, rotating clockwise.

Operation Dynamics of the Electric Motor

  • In subsequent diagrams:

    • Top brush contacts commutator B; electrons still flow down.

    • End A of armature becomes S-pole, repelled by S-pole of field magnet, continuing clockwise motion.

    • Electron tracing confirms end A becomes S-pole, attracting toward N-pole, facilitating full rotation.

  • Components of the motor:

    • Rotor: moving part.

    • Stator: stationary part.

  • Factors affecting speed of rotation:

    1. Magnitude of current flowing through motor.

    2. Strength of field magnet (stator).

    3. Number of coils on armature winding (rotor).

    4. Permeability of armature.

    5. Mechanical load on shaft.

Design and Operation of Analog Ammeter and Loudspeaker

  • Analog Ammeter:

    • Components include:

      • Flexible leads to coil.

      • Control suspension spring.

      • Permanent magnet.

      • Moving-coil mechanism.

  • Moving-Coil Loudspeaker:

    • Components include:

      • Soft iron core.

      • Voice coil and sound cone.

      • Permanent counter magnet.

  • Functionality:

    • Converts electrical signals into sound waves or measures current using movement of coil within a magnetic field.