MYP Physics: Voltage & Resistance (Ohm's Law) FAQ

You need three things: the definitions of voltage, current and resistance; Ohm's law (V = IR) and how to rearrange it; and how to read a circuit diagram to find these values practically. MYP assessment focuses on applying the formula correctly and explaining what a graph of V against I actually shows.

Ohm's law states that voltage equals current multiplied by resistance: V = IR, where V is in volts, I in amps and R in ohms. Rearrange it as I = V/R to find current, or R = V/I to find resistance. It only holds for components with constant resistance, called ohmic conductors.

Voltage is the energy given to each unit of charge as it moves through a circuit — think of it as the 'push'. Current is the rate at which charge actually flows, measured in amps. A battery sets the voltage; the circuit's resistance determines how much current that voltage produces.

Non-ohmic components — like filament lamps and diodes — don't have constant resistance because it changes with temperature or current direction. As a filament bulb heats up, its resistance increases, so its V-I graph curves instead of forming a straight line through the origin.

In series, total resistance is simply the sum of each resistor: R_total = R1 + R2 + R3. In parallel, it's more complex — the reciprocal of total resistance equals the sum of the reciprocals: 1/R_total = 1/R1 + 1/R2. Parallel resistance is always lower than the smallest individual resistor.

Use standard IB/MYP circuit symbols — a circle with an A for ammeter, a circle with a V for voltmeter. Ammeters always connect in series (in the main current path); voltmeters always connect in parallel (across the component you're measuring). Getting this reversed is the single most common practical mistake.

A strong investigation varies one thing (usually wire length or a variable resistor), keeps everything else constant, and takes repeated readings of voltage and current to calculate resistance each time. MYP Criterion B rewards a clear, testable hypothesis; Criterion C rewards accurate data collection and honest discussion of uncertainties.

It's not conceptually hard, but it's mark-heavy because it mixes recall (definitions), maths (rearranging V=IR) and practical skills (reading circuits) in one topic. Students who lose marks usually understand the physics fine but slip up on unit conversions or connecting meters the wrong way round in practicals.

Top marks come from combining accurate calculations with genuine explanation — not just stating V = IR but explaining what changing resistance does to current at constant voltage, and backing it up with real circuit data. Practise past-paper style questions that ask you to 'explain' or 'justify', not just 'calculate'.

Voltage is measured in volts (V), current in amps (A), and resistance in ohms (Ω). Watch for prefixes — milliamps (mA) need converting to amps (divide by 1000) before you plug numbers into V = IR, and this single conversion mistake accounts for a large share of lost marks in practical write-ups.

MYP Physics introduces voltage, current and resistance at a conceptual and single-formula level (V=IR). DP Physics — first examined under the current 2025 guide — extends this into resistivity, internal resistance, EMF and circuit analysis with series/parallel combinations assessed at much greater mathematical depth, especially at Higher Level.

A tutor who's examined MYP Physics can spot exactly where your child's understanding breaks down — usually unit conversions, meter placement in circuits, or explaining graphs rather than just describing them. Targeted one-to-one sessions on this single topic often move a student a full grade boundary within a few weeks.

Start with your school's MYP Physics unit materials, then supplement with topic-specific practice questions covering both calculations and circuit-diagram interpretation. RevisionPrep's MYP Physics hub includes worked examples on Ohm's law alongside guidance on the wider electricity and magnetism unit for continued revision.