Electricity and electromagnetism

Practice

Recall it first, then use it — testing yourself builds the memory, where rereading the notes above only feels easier.

Recall and application shuffled together — you have to work out what each item wants before you can answer it, which is the part the exam actually tests. Both kinds feed the same spacing schedule, so anything you miss comes back sooner.

Say the answer out loud before flipping — that attempt is where the learning happens, even when you get it wrong.

Exam-style only. Instant feedback, shuffled each attempt, best score saved on this device.

What actually comes up

Three questions every year, in the same order: electric fields (a parallel-plate setup, always with a calculation and a "use physics principles to explain" part), circuits (series/parallel with a fault or change introduced partway through), and electromagnetism (a motor, generator, or moving-conductor setup). The Excellence part is nearly always "use physics principles to explain" or "discuss" — a full, linked chain of reasoning, not just a number.

Across 3 years

The pattern — what to prepare

The 2025 paper ↗ Marking schedule ↗

Question One — Electric fields

Inkjet printers use a voltage across parallel plates, 1.00 mm apart, to aim charged ink droplets.

• Plate separation: 1.00 mm
• Droplet charge: 4.80 × 10⁻¹⁰ C, force: 9.60 × 10⁻⁴ N

• a Draw the field lines between the electric plates and the charge of the top plate. Achieved
• b Calculate the voltage across the plates when an ink droplet with a charge of 4.80 × 10⁻¹⁰ C is subjected to a force of 9.60 × 10⁻⁴ N. Merit
• c The voltage is changed to 4000 V. An ink droplet of mass 1.02 × 10⁻¹¹ kg, carrying 4.00 × 10⁹ excess electrons, is released from the negative plate. Calculate its velocity as it reaches the positive plate. Excellence
• d Discuss how it is possible for a charged ink droplet to be stationary between the plates — the forces on it, their directions, how they combine, and what type of charge it must have. Excellence

Question Two — Circuits

An air fryer has a heating element (a rheostat), two identical fan resistors, and a lamp, on a 240 V supply. Initially switch A is closed and B is open, so the element and lamp are on and the fans are off.

• Supply: 240 V
• Rheostat (element): 1000 Ω initially
• Fan resistors: 480 Ω each

• a Calculate the current in the lamp. Achieved
• b Use physics principles to explain what adjustment would need to be made to the rheostat's resistance to increase the power output of the element. Merit
• c Both switches are now closed and the heating element is set so it produces 1800 W. Show the resistance of the element is 32 Ω, and calculate how many coulombs of charge are produced by the supply in 5 minutes. Excellence
• d The lamp stops working. Use physics principles to explain the effect on the current in the circuit and on the power output of the element. Excellence

Question Three — Magnets

A current-carrying wire sits between the poles of a horseshoe magnet, crossing the field at right angles; a force acts on the wire in a shown direction. A 40-turn coil motor is also given, with a 15 N force on side AB.

• Coil turns: 40
• Force on side AB: 15 N
• Magnetic field strength: 1.7 T
• Length of AB: 50 cm

• a Which of the labelled poles is the north pole? Achieved
• b State the direction of current flow in the coil, and the size and direction of the force on side CD and on side BC, explaining the difference using physics principles. Excellence
• c The magnetic field strength is 1.7 T and the length of AB is 50 cm. Calculate the current in one strand of wire on side AB. Merit
• d By removing the voltage source, the motor becomes a generator. Calculate the speed side AB must move to generate a maximum of 12 volts in the coil, and explain what position side AB needs to be in to produce the maximum voltage. Merit

The 2024 paper ↗ Marking schedule ↗

Question One — Parallel plates

Parallel plates 0.06 m apart; an electron is released from the negative plate. A simplified Millikan oil-drop apparatus holds a charged oil drop stationary between plates.

• Plate separation: 0.06 m
• Oil drop mass: 1.95 × 10⁻¹⁵ kg
• Voltage across plates: 6.54 × 10² V
• Plate separation (oil drop): 2.19 cm

• a Select one of two labelled 12 V cells and correctly connect it to the plates to produce the field shown. Achieved
• b Ignoring gravity, calculate the speed of the electron when it reaches the positive plate. Excellence
• c Draw the path of an electron moving into the field from left to right, ignoring gravity, and use physics principles to explain the path, referring to the relevant force(s) and their directions. Merit
• d An oil drop of mass 1.95 × 10⁻¹⁵ kg with charge q is held stationary. Add labelled arrows for the two forces keeping it stationary, then calculate the number of excess electrons on the droplet to the nearest whole number. Excellence

Question Two — Circuits

A harvester circuit has three identical warning lamps B, C and D, with a variable resistor (dimmer switch) initially set to 3.5 Ω; the current in lamp D is 1.4 A.

• Variable resistor: 3.5 Ω
• Supply: 12 V
• Current in lamp D: 1.4 A

• a Explain why the current in lamp B is 0.70 A. Merit
• b Show the resistance of a single lamp is 3.3 Ω. Achieved
• c Explain what would happen to the brightness of lamp D if lamp B were to stop working. Excellence
• d With all three lamps working, the resistor is adjusted so lamp D converts 530 J of energy into light every minute. Calculate the total current in the circuit. Excellence

Question Three — Electromagnetism

A tractor with a 9.8 m metal sprayer boom moves at 4.1 m s⁻¹ across a paddock, in the vertical component of the Earth's magnetic field. A wire along the boom connects two warning lamps (6 V, 3 W each) to a 12 V battery.

• Boom length: 9.8 m
• Speed: 4.1 m s⁻¹
• Vertical field component: 31 × 10⁻⁶ T
• Battery: 12 V
• Each lamp: 6 V, 3 W

• a Clearly label the negative end of the sprayer boom. Achieved
• b Calculate the voltage induced between the ends of the sprayer boom. Achieved
• c Use physics principles to explain how the voltage is induced between the ends of the boom. Excellence
• d While stationary, the warning lights are activated by the 12 V battery. Indicate the direction of the electromagnetic force on the wire along the boom, and calculate the force acting on it. Excellence

The 2023 paper ↗ Marking schedule ↗

Question One — Parallel plates

Parallel plates 0.05 m apart, connected to 12 V. An electron moves between two different pairs of points on the diagram.

• Plate separation: 0.05 m
• Supply: 12 V

• a Show that the electric field strength between the plates is 240, and state its unit. Achieved
• b Draw the electric field lines representing the field between the plates. Merit
• c Use physics principles to explain how the electric force on an electron would vary as it moves from the negative plate to the positive plate. Merit
• d Calculate the change in electric potential energy as an electron moves between two named points along the field, then between two points across the field, and use physics principles to explain the difference between the two. Excellence

Question Two — Circuits

A simplified camping-oven circuit has a top section (a 6.2 Ω element and a 4.2 Ω lamp) and a bottom section (an 8.2 Ω resistor and a 4.2 Ω lamp), on a 12 V supply.

• Top section: 6.2 Ω element, 4.2 Ω lamp
• Bottom section: 8.2 Ω resistor, 4.2 Ω lamp
• Supply: 12 V

• a Show that the total resistance of the top section is 2.5 Ω. Achieved
• b Calculate the current flowing from the power supply to the oven when both sections are working. Merit
• c While both sections work correctly, the lamp in the bottom section develops a fault and its resistance decreases. Use physics principles to explain what happens to the brightness of the other lamp. Excellence
• d The lamp in the bottom section now stops working. Calculate the energy converted to heat in two minutes by the 8.2 Ω resistor. Excellence

Question Three — Electromagnetism

A metal axle rolls freely on two parallel metal rails in a magnetic field; the rails connect to a 120 V power supply.

• Magnetic field: 8.10 × 10⁻³ T
• Axle length: 0.950 m
• Rail separation: 0.840 m
• Total effective resistance: 42.1 Ω
• Supply: 120 V
• Axle speed (parts c–d): 3.10 m s⁻¹

• a Draw an arrow to show the direction of the electromagnetic force on the axle when the power supply is switched on (or state clearly if there is none). Achieved
• b Calculate the strength of the magnetic force on the axle when the power supply is turned on. Merit
• c The power supply is removed and the axle is pushed to the right at 3.10 m s⁻¹. Mark the negative end of the axle, and calculate the voltage induced immediately after it is set moving. Merit
• d With the power supply still disconnected, a wire is connected between the rails and the axle is pushed at 3.10 m s⁻¹. Describe the motion of the axle after it is set moving, and justify your answer using electromagnetism physics principles. Excellence

Grades above are read from each year's own Achievement/Merit/Excellence evidence statement, condensed to the actual task — the schedules also grade holistically per question on a 0–8 scale, not a fixed mark per bullet.

Past exams & resources

⏱ Timed opens the paper and starts a countdown matching the exam length. Official NZQA PDFs. If a link 404s, that year’s paper may sit under a slightly different code: browse the NZQA subject page.