Electricity & Magnetism · GCSE Physics Topic 7 (Electric Motors)
DC Electric Motor & Commutator Simulator
Key exam takeaway: The split-ring commutator reverses the coil current direction each time it passes the neutral equilibrium plane, ensuring continuous unidirectional torque.
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3D Simulation Stage● 60 FPS
Parameter Controls
A
T
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Live Derivations & Metrics
Instantaneous Torque τ
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Estimated Speed
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Left Arm Force Direction
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Right Arm Force Direction
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Real-Time Formula Derivation
Governing Formula:
--Substitution:
--Regime: --
Worked Examples & Exam Question Deep Dive
Worked Problem
Problem: What energy conversion occurs in a DC motor? What happens if you forcefully stall the rotor shaft?
Step-by-Step Derivation:
- Converts electricity to mechanical work. Stalling eliminates back-EMF; low coil resistance causes massive current inrush, burning windings in seconds.
Worked Problem
Problem: What components constitute a commutator? How does it reverse current timing precisely?
Step-by-Step Derivation:
- Consists of two insulated semi-cylindrical copper split-rings and two stationary carbon brushes. As rotor passes neutral plane, contacts swap brushes, reversing current.
Student Inquiry Worksheet & Practice Problems
Q1. Variant 1: What two separate actions reverse DC motor rotation? What if you reverse both current and magnets?
Answer Key: Reverse either current direction OR magnetic polarity. Reversing both simultaneously leaves rotation direction unchanged (double reversal).
Q2. Variant 2: What two common adjustments increase DC motor rotational speed?
Answer Key: 1) Increase armature current (boost voltage); 2) strengthen stator magnetic field (stronger magnets or excitation current).
Q3. Variant 3: What is the motor's "neutral equilibrium plane"? Can it self-start if stopped exactly on dead center?
Answer Key: Plane perpendicular to field lines where opposing forces are collinear (zero torque) and brushes bridge the gap. It cannot self-start without a push.
Frequently Asked Questions & Misconceptions
DC motors and generators have identical structures. What is their core physical distinction?
Causality is inverted: Motors take electricity to produce mechanical motion (Lorentz force). Generators take motion to produce electricity (Faraday induction).
Why do modern Brushless DC (BLDC) motors dominate over brushed motors?
Brushed motors spark and wear carbon contacts. BLDC motors invert structure: permanent magnets on rotor, electronic transistor switching (ESC) eliminates friction.
How do electric vehicles recover braking kinetic energy into battery recharge?
Regenerative braking! Inverter switches traction motor into generator mode. Wheel rotation generates electricity back into battery pack while damping the car.
Why does a jammed toy motor emit a burning smell after a couple of minutes?
Spinning rotors generate opposing Back-EMF. Stalling drops Back-EMF to zero, forcing massive current through tiny coil resistance, vaporizing enamel.