OxfordAQA International GCSE Physics 3.5 Electricity and Magnetism Exam Questions

About OxfordAQA International GCSE Physics 3.5 Electricity and Magnetism

Electricity and Magnetism in OxfordAQA International GCSE Physics covers the basic ideas of circuits and magnetic fields. You learn charge and current, potential difference as energy per unit charge, resistance and V = I x R, circuit symbols, and how lamps, diodes, thermistors and LDRs behave. Series and parallel circuit rules are essential. Separate Physics adds static electricity and some component details. The magnetism part covers poles, field patterns, induced magnets, the Earth's field, fields around wires and solenoids, and electromagnets. It leads into generators, transformers and the motor effect in 3.6. Examiners frequently test V-I graphs and series circuit calculations.

What you need to know

• Charge and current Current is the rate of flow of charge: I = Q / t. Metals contain free electrons that move easily. Static electricity (separate Physics) is an imbalance of charge that discharges when a conducting path forms, as in lightning.
• Potential difference Potential difference is the energy transferred per unit charge: V = E / Q. The pd of cells in series add up.
• Resistance V = I x R. For a resistor at constant temperature, current is directly proportional to pd. A filament lamp's resistance increases as it gets hotter because ions vibrate more and impede electrons. Thermistor resistance falls as temperature rises; LDR resistance falls as light intensity rises.
• Diodes and LEDs A diode has a very high resistance in reverse, so current flows one way only. An LED emits light when current flows forwards and uses much less current than other lamps.
• Series and parallel Series: total resistance is the sum, current is the same everywhere and the supply pd is shared. Parallel: total resistance is less than the smallest branch, current splits between branches and each branch has the full pd.
• Required practicals Investigate the V-I characteristics of a filament lamp, a diode and a resistor at constant temperature (separate Physics), and investigate the factors that determine the strength of an electromagnet.
• Magnets and fields Like poles repel, unlike attract. Iron, steel, cobalt and nickel are magnetic. Field lines go from north to south and are parallel in a uniform field. An induced magnet is always attracted and loses most of its magnetism when removed.
• Electromagnetism A current in a wire produces circular field lines around it, stronger near the wire and with more current. A solenoid gives a field like a bar magnet with a strong uniform field inside; adding an iron core makes an electromagnet.

Common mistakes in 3.5 Electricity and Magnetism

• Connecting a voltmeter in series. A voltmeter goes in parallel across the component; an ammeter goes in series.
• Saying current is used up around a series circuit. Current is the same at every point in a series circuit.
• Saying total resistance increases when resistors are added in parallel. It decreases, because there are more paths for current.
• Describing a filament lamp graph as a straight line. It curves because resistance increases as the filament heats up.
• Saying a thermistor's resistance increases with temperature. For the thermistors studied, resistance decreases as temperature rises.

Try three 3.5 Electricity and Magnetism exam-style questions