Electric Circuits & Electrical Safety
Master circuit behaviour, voltage, resistance, and how to stay safe around electricity.
- Series circuits: Single loop, current same everywhere, voltage splits between components, resistances add
- Parallel circuits: Multiple loops, current splits at junctions, voltage same across each branch, resistances combine differently
- EMF vs potential difference: EMF is what the power source supplies; potential difference is voltage across a component
- Potential dividers: Two resistors in series split voltage in the ratio of their resistances
- Electrical hazards: Damaged insulation, overheating, damp conditions, overloading can cause electrocution or fire
- Safety devices: Double insulation, earthing, fuses, circuit breakers all protect you from danger
Circuit Symbols & Components
Before you can work with circuits, you need to recognize and understand what each component does. Every symbol represents a real electrical object, and each one behaves differently.
Power Sources
These supply energy to the circuit. A cell produces a steady voltage (like a battery). Multiple cells connected in series add their voltages together. A power supply or generator supplies current continuously to a circuit.
Resistors & Resistance Devices
These control how much current flows. A fixed resistor always has the same resistance. A variable resistor can be adjusted (like a volume knob). More resistance = less current flows through.
Thermistors are special: their resistance changes with temperature. When temperature increases, resistance decreases, and vice versa. They're used in thermostats and temperature sensors.
Light-dependent resistors (LDRs) change resistance based on light. More light = less resistance. They're used in automatic street lights and light sensors.
Meters
Ammeters measure current in amps (A). They always connect in series (in line with the circuit) so all current flows through them. Think of them as a flow counter in a pipe.
Voltmeters measure potential difference in volts (V). They always connect in parallel (across the component you're measuring) to avoid changing the circuit. They have very high resistance so almost no current flows through them.
Key rule: Ammeter = series. Voltmeter = parallel. If you get this backwards, you'll get wrong answers (or break equipment in a real lab).
Switches & Functional Components
Switches turn circuits on and off by opening or closing the circuit path.
Functional components do something useful:
- Lamps emit light
- Motors rotate
- Heaters transfer thermal (heat) energy
- Bells emit sound
Electromagnetic Components
Transformers change voltage (step up) or reduce it (step down). They're essential in power distribution because they allow voltage to be changed without losing too much energy.
Relays use a small current in one circuit to switch on a much larger current in another circuit. They're like electrical switches controlled by electricity itself.
Diodes & LEDs
A diode is a one-way valve for electricity. It only allows current to flow in one direction (the direction the triangle points in the symbol). If you flip it backwards, no current flows.
Light-emitting diodes (LEDs)
Fuses
fuse
Which component always goes in parallel with the component you want to measure voltage across?
Combined Resistance