Module 6: Electromagnetism
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HSC Physics 2026: recall practice based on the 2017 syllabus.
72 Terms
What direction defines an electric field?
The force direction on a positive test charge.
What direction is the electric force on an electron relative to the field?
Opposite to the electric field.
Which supplied equation relates electric force to charge and field?
F⃗ = qE⃗.
For ideal parallel plates what is the electric field magnitude?
E = V/d, away from edge effects.
What direction does the electric field point between oppositely charged plates?
From the positive plate to the negative plate.
How does a uniform electric field affect a stationary charge?
It produces constant acceleration along or opposite the field.
Why can a charged particle between uniform electric plates follow a parabola?
Constant transverse acceleration combines with constant longitudinal velocity.
What is one electronvolt?
The energy gained by one elementary charge across one volt.
What is the magnetic force direction on a moving positive charge?
Perpendicular to both velocity and magnetic field.
How does the magnetic force direction change for a negative charge?
It reverses relative to a positive charge.
Which supplied equation gives magnetic force magnitude on a moving charge?
F = |q|vB sin θ.
When is magnetic force on a moving charge greatest?
When velocity is perpendicular to the magnetic field.
When is magnetic force on a moving charge zero?
When velocity is parallel or antiparallel to the field.
What work does a static magnetic field do on a charged particle?
Zero; magnetic force is perpendicular to velocity.
What path does a charged particle follow when velocity is perpendicular to a uniform magnetic field?
A circle at constant speed.
What path does a charged particle follow with velocity components parallel and perpendicular to a uniform field?
A helix.
How can the radius of a charged particle's circular magnetic path be found?
Set |q|vB = mv²/r.
How does an electric field differ from a magnetic field in work on a charge?
An electric field can change kinetic energy; a magnetic field cannot.
What direction does conventional current flow relative to electron flow?
Opposite to electron flow.
Which supplied equation gives force on a straight current-carrying wire in a uniform field?
F = BIL sin θ.
What angle is used in F = BIL sin θ?
The angle between current direction and magnetic field.
When is the motor-effect force on a straight wire maximum?
When current is perpendicular to the magnetic field.
What is the magnetic force on a wire parallel to a uniform magnetic field?
Zero.
How do two parallel wires carrying currents in the same direction interact?
They attract.
How do two parallel wires carrying currents in opposite directions interact?
They repel.
How do the forces between two current-carrying wires compare?
Equal magnitude and opposite direction.
What does the current SI definition of the ampere fix?
The numerical value of the elementary charge.
What did the former ampere definition use?
Force per length between ideal parallel wires in vacuum.
What is magnetic flux through a flat surface in a uniform field?
Φ = BA cos θ, where θ is to the surface normal.
What is the SI unit of magnetic flux?
The weber (Wb).
How can magnetic flux through a loop change?
Change field strength, loop area, or orientation.
What causes an induced electromotive force in a loop?
A change in magnetic flux linkage.
What does Faraday's law relate induced EMF to?
The rate of change of magnetic flux linkage.
What does Lenz's law determine?
The induced current's direction opposes the change in flux.
Why is Lenz's law consistent with energy conservation?
Opposing the change requires external work to supply energy.
What is required for an induced EMF to produce a sustained current?
A closed conducting path.
How can a stationary primary coil induce EMF in a nearby secondary coil?
A changing primary current changes linked magnetic flux.
How does increasing the rate of change of flux affect induced EMF magnitude?
It increases the magnitude.
How does doubling the number of turns affect induced EMF for the same flux change per turn?
It doubles the magnitude.
What input does a conventional transformer need for continuous operation?
A changing current, normally alternating current.
Which supplied equation gives an ideal transformer's voltage ratio?
Vₚ/Vₛ = Nₚ/Nₛ.
What condition identifies a step-up transformer?
The secondary has more turns than the primary.
What condition identifies a step-down transformer?
The secondary has fewer turns than the primary.
What is conserved between input and output in an ideal transformer?
Power: VₚIₚ = VₛIₛ.
Why does high-voltage transmission reduce resistive losses for fixed power?
Lower current reduces I²R heating.
How do laminated transformer cores reduce eddy-current losses?
Insulating layers restrict circulating currents.
Why use a soft iron transformer core?
It improves magnetic flux linkage between coils.
What does incomplete flux linkage cause in a transformer?
Some primary flux does not link the secondary.
What energy transformation occurs in resistive transformer windings?
Electrical energy becomes thermal energy.
What is the function of a split-ring commutator in a DC motor?
It reverses coil current each half-turn.
What provides torque on a current-carrying motor coil?
Opposite magnetic forces on opposite sides of the coil.
Which supplied equation gives torque on a planar N-turn coil?
τ = NIAB sin θ, with θ between coil normal and field.
What is back EMF in a motor?
Induced EMF opposing the applied voltage.
How does motor back EMF usually change as motor speed rises?
It increases in magnitude.
Why is starting current large in a simple DC motor?
At rest, back EMF is initially zero.
What energy conversion occurs in a generator?
Mechanical energy to electrical energy.
What electrical connection produces alternating output in a simple AC generator?
Slip rings.
What electrical connection produces pulsating unidirectional output in a simple DC generator?
A split-ring commutator.
What creates the rotating magnetic field in an AC induction motor?
Alternating currents in the stator windings.
Why does an induction motor rotor turn?
The rotating field induces currents that experience magnetic torque.
Why must an induction motor rotor run below synchronous speed under load?
Relative motion is needed to induce rotor currents.
How does magnetic braking slow a moving conductor?
Eddy currents produce a force opposing the motion.
Where does energy go during magnetic braking?
Mechanical energy is mainly transformed into thermal energy.
What sign convention gives work done by the electric field between two potentials?
Wfield = q(Vinitial − Vfinal).
How does the electric potential energy of a charge change when the electric field does positive work?
It decreases by the work done by the field.
How is magnetic field direction around a straight current-carrying wire found?
Right-hand grip: thumb along conventional current, fingers along field.
How does field strength change with distance from a long straight wire?
It varies inversely with radial distance.
How can the force between parallel wires be investigated quantitatively?
Vary current or separation and measure force per length.
What changes the direction of the induced current when a magnet moves through a coil?
Reversing the change in magnetic flux reverses the current.
What limits an ideal transformer's perfect power transfer in a real transformer?
Resistance, eddy currents, hysteresis and incomplete flux linkage.
What is the role of brushes in a simple DC motor?
They maintain electrical contact with the rotating commutator.
Why does an externally driven generator require mechanical work when supplying current?
Induced current produces torque opposing rotation.