A DC (Direct Current) motor is a fundamental application of the motor effect that converts electrical energy into continuous mechanical rotational energy.

Operating Principles & Physics Theory

When a rectangular current-carrying coil (the armature) is placed in a uniform magnetic field, the opposite sides of the coil experience equal and opposite magnetic forces according to F = BIl sin(θ). Because these forces act along different lines of action on either side of the pivot axis, they produce a net torque (τ), causing the loop to rotate:

Where:

• τ is the torque in Newton-meters (N·m)
• n is the number of turns in the wire coil
• B is the magnetic field strength in Teslas (T)
• I is the electric current in Amperes (A)
• A is the area of the coil in square meters (m²)
• θ is the angle between the plane of the coil and the magnetic field lines

The Role of the Split-Ring Commutator

As the coil rotates past the perpendicular position (θ = 90°), the direction of torque would naturally reverse, causing the loop to oscillate back and forth rather than spinning continuously. To overcome this, a split-ring commutator reverses the direction of current flowing through the coil every half-rotation (180°). This ensures that the torque remains unidirectional, keeping the motor spinning continuously in one direction.

The following video breaks down these key structural components, force vectors, and mathematical relationships in detail.