Physics / IGCSE
Build circuit and field models, then connect them to useful devices.
Charge is conserved at circuit junctions, and energy per unit charge is shared around loops. In series, resistance adds; parallel branches have the same potential difference across them.
Currents create magnetic fields, and a current in a magnetic field can experience a force. A changing magnetic flux can induce an emf. Electrical safety depends on suitable insulation, protective devices and safe working procedures.
Magnets have north and south poles; like poles repel and unlike poles attract. Field lines indicate the force direction on a north test pole and are closer where the field is stronger. Electric charge is different from a magnetic pole. Rubbing can transfer electrons between materials without creating net charge. Current I = Q/t measures charge transfer, with conventional direction opposite electron drift in a metal.
Potential difference is energy transferred per unit charge across a component; source emf is energy supplied per unit charge. For an ohmic resistor at constant temperature, V = IR. A filament lamp heats as current rises, so its resistance changes. A diode conducts far more readily in one direction. Thermistors and light-dependent resistors allow circuits to respond to temperature and light without being ideal fixed resistors.
Ammeter connections are in series and voltmeter connections are across two points. Series components have one current and share voltage; parallel branches share voltage and split current. For example, two equal resistors in parallel draw twice the current of one at the same supply voltage. Closing a switch changes the network, so re-evaluate the circuit rather than applying a remembered series rule to every branch.
Electrical power is VI and energy is VIt under steady conditions. A 60 W device operated for 2 h transfers 120 Wh, or 0.12 kWh; a kilowatt-hour is energy, not power. Fuses and circuit breakers interrupt excessive current; insulation and suitable earthing or double insulation address other hazards. Protective devices do not make careless contact with mains electricity safe. Use only low-voltage classroom circuits and never modify mains wiring.
A current produces a magnetic field, strengthened in a coil by suitable core material. A current-carrying conductor in a field can experience a force, providing the principle of a motor. Relative movement that changes flux linkage can induce emf, providing the generator principle. A transformer uses changing flux to transfer energy between coils, with voltage ratio set approximately by turns ratio in the ideal case. It does not operate steadily from an unchanging direct current.
The added branch lowers the load’s equivalent resistance and permits more charge per second to circulate. Charge remains conserved; the source transfers energy at a greater rate.
Electrical power transferred by a component.
Energy at constant voltage and current.
A low-voltage lamp operates at 6 V and 0.5 A. What power does it transfer?
P = VI = 6 × 0.5 = 3 W.
Move a magnet into a coil in a simulation and compare slow and fast movement. Never experiment with mains wiring.
Build and measure circuits before trying motors or induction. These models do not reproduce every fault or protective system and must never be treated as mains-safety demonstrations.
Potential difference across each branch
Parallel branches connect across the same pair of points.
3 W
P = VI = 6 × 0.5 = 3 W.
Changing the magnetic flux through it
Induction requires a change in magnetic flux linkage.