QCE Physics · Unit 3
QCE Physics Unit 3 Topic 2: Electromagnetism — Flashcards & Quiz
QCE Physics Unit 3 Topic 2 examines the interplay between electric and magnetic fields and how they underpin modern technology. These free flashcards and true/false questions cover Coulomb's law, electric field strength, magnetic fields around conductors, the motor effect, electromagnetic induction, Faraday's law, Lenz's law, AC generators, transformers, and power transmission. Every card is aligned to the QCAA Senior Physics syllabus so you study exactly what examiners test. Strengthen your understanding of field interactions, induced EMF and energy transfer through spaced repetition.
Key Terms
- Motor effect
- The force experienced by a current-carrying conductor placed in an external magnetic field, calculated as F = BIL sin(theta). QCAA Physics Unit 3 Topic 2 EA questions require students to apply the right-hand rule to determine force direction and explain how this principle operates in DC motors.
- Faraday's law of electromagnetic induction
- The law stating that the magnitude of the induced EMF equals the rate of change of magnetic flux through a coil multiplied by the number of turns: EMF = negative N times delta(flux)/delta(t). QCAA external assessments require students to calculate induced EMF from given flux change data and explain each variable.
- Lenz's law
- The principle that the direction of an induced current is always such that it opposes the change in magnetic flux that produced it, consistent with conservation of energy. QCAA Physics Unit 3 Topic 2 EA questions require students to determine current direction in induction scenarios and justify the answer using energy conservation reasoning.
- Magnetic flux
- The total magnetic field passing through a given area, calculated as flux = BA cos(theta) where B is field strength, A is area and theta is the angle between the field and the normal to the surface. QCAA assessments test students' ability to calculate flux changes and connect them to Faraday's law for EMF determination.
- Transformer
- A device that uses electromagnetic induction to step voltage up or down between primary and secondary coils, governed by Vp/Vs = Np/Ns. QCAA Physics Unit 3 Topic 2 EA questions require students to apply transformer equations, calculate efficiency and explain why high-voltage transmission reduces power loss using P = I squared R.
- Right-hand rule
- A convention for determining the direction of the magnetic force on a current-carrying conductor, the direction of the magnetic field around a current, or the direction of induced current. QCAA Physics assessments require consistent and correct application of this spatial reasoning tool across motor effect and induction problems.
Sample Flashcards
Q1: State Coulomb's law and define each variable.
F = kq₁q₂/r², where k = 8.99 × 10⁹ N m² C⁻², q₁ and q₂ are charges (C), r is separation (m). Attractive for unlike charges, repulsive for like charges.
Q2: Define electric field strength and give both formulas.
E = F/q (N C⁻¹): force per unit positive charge. Point charge: E = kQ/r². Parallel plates (uniform): E = V/d.
Q3: Describe electric field line patterns for point charges and parallel plates.
Point charge: radial lines outward (+) or inward (−), density ∝ 1/r². Parallel plates: uniform, straight, equally spaced from + to − plate. Edge fringing occurs at plate boundaries.
Q4: What is the work done on a charge moving through a potential difference?
W = qV, where W is work (J), q is charge (C), V is potential difference (V). Equals the change in kinetic energy if no other forces act.
Q5: Describe the magnetic field around a straight current-carrying conductor.
Concentric circles centred on the wire, strength decreasing with distance. Right-hand grip rule: thumb = conventional current direction, fingers curl = field direction.
Q6: What is the force on a current-carrying conductor in a magnetic field?
F = BIl sin θ. B = field strength (T), I = current (A), l = length in field (m), θ = angle between conductor and field. Max at 90°, zero at 0°.
Q7: What force acts on a charged particle in a magnetic field?
F = qvB sin θ. Always perpendicular to both v and B, causing circular motion. Does no work — changes direction, not speed.
Q8: Explain how a DC motor works using electromagnetic principles.
Current in a coil within a magnetic field experiences forces (F = BIl) in opposite directions on each side, creating a torque. A commutator reverses current every half-turn to maintain rotation in one direction.
Sample Quiz Questions
Q1: Coulomb's law follows an inverse-square relationship with distance.
Answer: TRUE
F = kq₁q₂/r² — F ∝ 1/r².
Q2: Like charges attract each other.
Answer: FALSE
Like charges repel; opposite charges attract.
Q3: Electric field lines point from negative to positive charges.
Answer: FALSE
Field lines point from positive to negative — the direction a positive test charge would move.
Q4: The field between parallel plates is uniform.
Answer: TRUE
Between the plates (ignoring edges), E = V/d is constant everywhere.
Q5: A stationary charge in a magnetic field experiences a magnetic force.
Answer: FALSE
F = qvB sin θ — if v = 0, F = 0. Magnetic force requires motion.
Why It Matters
Electromagnetism connects electric and magnetic fields and is one of the most application-rich topics in QCE Physics. The external exam tests your ability to apply the motor effect, explain electromagnetic induction using Faraday's and Lenz's laws, and analyse the operation of motors, generators and transformers. This topic demands strong spatial reasoning — you must visualise three-dimensional force, field and current relationships using the right-hand rule — alongside quantitative problem-solving with flux, EMF and transformer equations. Electromagnetism builds on the gravitational and electric field concepts from Topic 1 and has direct real-world relevance to electric motors, power generation and transmission systems. QCAA exam questions commonly present a generator or transformer scenario and ask you to apply Faraday's law to calculate the induced EMF, use Lenz's law to determine current direction, and explain the energy transformations involved.
Key Concepts
Magnetic Fields and the Motor Effect
Understand magnetic field patterns around bar magnets, straight conductors and solenoids. Apply F = BIL sin(theta) to calculate the force on a current-carrying conductor in a magnetic field. Use the right-hand rule to determine force direction, and explain how this principle operates in DC motors.
Electromagnetic Induction and Faraday's Law
Explain how a changing magnetic flux through a coil induces an EMF (Faraday's law: EMF = -N x delta(flux)/delta(t)). Understand that the magnitude of induced EMF depends on the rate of flux change and the number of turns. Apply this to generators and explain how AC is produced by a rotating coil in a magnetic field.
Lenz's Law and Energy Conservation
Apply Lenz's law to predict the direction of induced current — it always opposes the change that caused it. Understand this as a consequence of energy conservation and practise determining current direction in various induction scenarios including moving conductors and changing fields.
Transformers and Power Transmission
Explain how transformers use electromagnetic induction to step voltage up or down. Apply Vp/Vs = Np/Ns and the ideal transformer equation (VpIp = VsIs). Understand why high-voltage transmission reduces power loss (P = I^2R) and calculate efficiency in real transformer problems.
Common Mistakes to Avoid
- Confusing Faraday's law (magnitude of induced EMF) with Lenz's law (direction of induced current) — QCAA Physics Unit 3 Topic 2 EA marking guides expect students to apply both laws separately: Faraday's for calculating how much EMF is induced and Lenz's for determining which way the current flows.
- Mixing up the function of a commutator (DC motors/generators, reverses current direction) with slip rings (AC generators, maintain continuous contact) — QCAA assessments test this distinction in diagram-based questions about rotating coil devices.
- Forgetting the sin(theta) term in F = BIL sin(theta) when the conductor is not perpendicular to the field — QCAA EA calculation questions may present conductors at various angles, and omitting the angle correction leads to incorrect force values.
- Stating that transformers work with DC current — transformers require a changing magnetic flux, which only AC provides. QCAA Physics extended-response questions may ask students to explain why DC cannot be used with standard transformer designs.
Study Tips
- Practise the right-hand rule with a physical hand gesture for every problem — build muscle memory for determining force, field and current directions.
- Draw the operating cycle of a DC motor and an AC generator side by side, labelling the role of the commutator versus slip rings.
- Solve Faraday's law problems by first calculating the change in magnetic flux, then dividing by time — always include units in each step.
- Create a transformer problem set with step-up and step-down scenarios, including efficiency calculations.
- Use flashcards with spaced repetition to memorise electromagnetic equations and right-hand rule applications — confusing Faraday's law with Lenz's law or mixing up motor and generator operation is a common exam pitfall.
- Before your exam, work through the practice questions in this set at least twice using spaced repetition. Testing yourself repeatedly is the most effective revision strategy for long-term retention.
Related Topics
Frequently Asked Questions
What does QCE Physics Unit 3 Topic 2 cover?
Unit 3 Topic 2 covers Coulomb's law, electric fields, magnetic fields, the motor effect, electromagnetic induction, Faraday's law, Lenz's law, AC generators, transformers, and electrical power transmission.
How many flashcards are in this set?
This free set contains 20 flashcards and 20 true/false quiz questions covering all key electromagnetism concepts, aligned to the QCAA Senior Physics syllabus.
Are these aligned to the QCE syllabus?
Yes — every card maps to QCAA syllabus objectives for QCE Physics Unit 3 Topic 2: Electromagnetism.
Last updated: March 2026 · 20 flashcards · 20 quiz questions · Content aligned to the QCAA Syllabus