§-Module

Module 6: Electromagnetism

9 dot points across 5 inquiry questions, in syllabus order. Each dot point has a focused answer, with exam-style questions and worked answers where available.

Inquiry Question 1: What happens to stationary and moving charged particles when they interact with an electric field?

Model qualitatively and quantitatively the electric field, including direction and shape, produced between parallel charged plates and the potential difference, using E = V/d

Parallel plate electric field. Field shape, the meaning of uniform field, the relationship E = V/d, why E is independent of position between the plates, and the fringing effect at the edges.

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Investigate and quantitatively derive and analyse the interaction between charged particles and uniform electric fields, including: electric field between parallel charged plates E = V/d, acceleration of charged particles by the electric field F_net = ma, F = qE, work done on the charge W = qV, W = qEd, K = (1/2)mv^2

Charged particles in uniform electric fields. The parallel-plate formula E = V/d, the force F = qE, work-energy theorem W = qV, and a worked electron-gun example with traps to avoid.

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Inquiry Question 2: How does the motion of a charged particle in a magnetic field differ from its motion in an electric field?

Investigate quantitatively and analyse the interaction between current-carrying conductors and uniform magnetic fields F/l = I B sin theta, including parallel current-carrying wires F/l = mu_0 I_1 I_2 / (2 pi r)

Magnetic force on a current-carrying conductor. The single-wire result F = BIL sin theta, the parallel-wire result F/l = mu_0 I_1 I_2 / (2 pi r), the definition of the ampere, and direction by the right-hand rule.

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Analyse the interaction between charged particles and uniform magnetic fields, including: acceleration, perpendicular to velocity F = qv x B, circular motion of a charged particle moving perpendicular to a uniform magnetic field

Charges moving in magnetic fields. The Lorentz force qv x B, why it does no work, circular motion with radius r = mv/(qB), period T = 2 pi m / (qB), and the right-hand rule for direction.

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Inquiry Question 3: Under what circumstances is an electrical voltage generated by a magnetic field?

Describe how magnetic flux can be sensed by the changing alignment of a magnet on a compass needle and quantitatively analyse the concept of magnetic flux density B and flux Phi = B A cos theta in a magnetic field

Magnetic flux. The definitions of flux density B (tesla) and magnetic flux Phi (weber), the cosine factor for tilted loops, and a worked rotating-coil example with the right traps highlighted.

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Describe and quantitatively analyse electromagnetic induction using Faraday's law (induced EMF = - N dPhi/dt) and Lenz's law, including motional EMF, eddy currents and the induction coil

Electromagnetic induction. Faraday's law as EMF = -N dPhi/dt, Lenz's law and conservation of energy, motional EMF in a moving rod, eddy currents and damping, and the induction coil as a stepped-up pulse source.

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Inquiry Question 4: How are electric and magnetic fields applied in electrical generation, transmission and use?

Analyse the operation of DC and AC motors, including the torque on a current loop tau = n B I A cos theta, the role of the commutator, back EMF, and the AC induction motor principle

Motors. Torque on a current loop tau = nBIA cos theta, the split-ring commutator in DC motors, back EMF and its role in steady-state current, the rotating-field principle of the AC induction motor, and where each is used.

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Analyse the operation of ideal and real transformers, including the turns ratios V_s/V_p = N_s/N_p and I_p/I_s = N_s/N_p, energy losses, and the role of step-up and step-down transformers in AC power transmission

Transformers. Ideal voltage and current ratios, power conservation V_p I_p = V_s I_s, the four energy losses in real transformers, and why high-voltage AC transmission minimises line losses.

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Inquiry Question 4: How has knowledge about the Motor Effect been applied to technological advances?

Analyse the operation of AC and DC generators, including the role of slip rings and the split-ring commutator, the sinusoidal emf epsilon = NBA omega sin(omega t), peak and RMS voltage and current, and the advantages of AC over DC for electricity generation and transmission

Generators. AC generators (slip rings) give sinusoidal emf epsilon = NBA omega sin(omega t); DC generators (split-ring commutators) give rectified emf; peak vs RMS values; why AC and transformers won electricity transmission by cutting I^2 R line loss.

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