HomePhysicsP6: Magnetism and ElectromagnetismP6.3 The Motor Effect and Electric Motors

P6: Magnetism and Electromagnetism

P6.1 Magnetism – Magnets and Magnetic FieldsP6.2 Electromagnets – Coils and CurrentP6.3 The Motor Effect and Electric MotorsP6.4 Generators and Transformers
P6: Magnetism and Electromagnetism

The Motor Effect and Electric Motors

Understand how current in a magnetic field creates force and how motors work

Electric motor

Electric Motors

Converting electricity to motion

The Motor Effect
Force on a current-carrying conductor

When a current-carrying conductor is placed in a magnetic field, it experiences a force. This is the motor effect, described by:

F = BIL

Force = Magnetic field × Current × Length in field

The force direction is perpendicular to both the current and the magnetic field. Use Fleming's Left-Hand Rule: First finger = Field, seCond finger = Current, thuMb = Motion.

How an Electric Motor Works
Converting electrical energy to kinetic energy

A simple DC motor consists of a coil of wire that can rotate between the poles of a magnet. When current flows through the coil:

  1. Current flows through the coil in the magnetic field
  2. The motor effect creates forces on opposite sides of the coil
  3. These forces act in opposite directions, causing the coil to rotate
  4. The split-ring commutator reverses current every half turn
  5. This maintains rotation in the same direction continuously
Increasing Motor Speed
Factors affecting motor performance

Motor speed can be increased by:

Stronger Field (B)

Use stronger magnets

Larger Current (I)

Increase voltage or reduce resistance

More Turns

More wire loops in the coil

Electric Motor Simulator
See how the motor effect creates rotation and adjust parameters to change speed
NS×Split-ring commutatorCarbon brushes

Motor Speed

13%

Motor Effect Formula

F = BIL

Force = Field × Current × Length

How It Works

Current flows through the coil in a magnetic field. The motor effect (F=BIL) creates forces on opposite sides of the coil in opposite directions, causing rotation. The split-ring commutator reverses current direction every half turn to maintain continuous rotation.

Key Terms Flashcards
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Motor Effect

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Worked Example
Calculating motor effect force

Question:

A wire of length 0.2 m carries a current of 3 A perpendicular to a magnetic field of 0.5 T. Calculate the force on the wire.

Answer:

Using F = BIL:

F = 0.5 × 3 × 0.2

F = 0.3 N

Test Your Knowledge
Question 1 of 6

What is the formula for the motor effect force?