Electrical Circuits

• The formula for Ohm's Law is V = IR, where V is the voltage, I is the current, and R is the resistance.
• Resistors control current flow in a circuit by resisting the flow of electricity and have two terminals
• Made from metal wire or carbon, with carbon resistors common for high-resistance applications due to lower conductivity
• Variable resistors allow adjustment of resistance and are often used for volume control in electronic devices
• Light-Dependent Resistors (LDR) have resistance that changes based on light intensity and are used in circuits for light detection, like in security lights
• Thermistors have resistance that changes with temperature and are utilized in temperature sensors and control circuits
• Diodes allow current flow in one direction only and are represented by an arrow in their circuit symbol
• Light-emitting diodes (LEDs) emit light when current flows through them and are commonly used as indicator lights and in traffic lights for energy efficiency
• Relays are switches operated by electromagnets, with two circuits: one for the electromagnet and one for the switch
• When current flows through the electromagnet circuit, it magnetizes, closing the switch in the other circuit
• Relays can sense changes in temperature or light level, controlling other components based on these changes
• A circuit can turn on a lamp when the temperature rises or detect changes in light level for security purposes
• The resistance of a thermistor or LDR changes with temperature or light level, respectively, affecting the current flow through the relay coil, which activates the relay switch to control other circuit components
• Parallel Circuits:

  • Combined resistance is calculated differently
  • Effective resistance is less than individual resistors
  • Greater current from the source than through any resistor
• Advantages of Parallel in Lighting:

  • Lamps connected in parallel maintain full voltage
  • Individual operation, if one fails others remain lit
• Series Circuits:

  • Combined resistance is the sum of individual resistances
  • Current is the same at all points
  • Larger resistance leads to a larger potential difference (p.d.)
• Potential Divider Circuits:

  • Split fixed potential difference into smaller or variable p.d.
  • Can use resistors in series, sometimes with variable resistor for variable output
• Current and Resistance in Circuits:

  • Current is conserved; total current entering a junction equals total leaving
  • In parallel circuits, current divides; in series, it's the same throughout
• Complex Circuits Analysis:

  • Equivalent circuits simplification for analysis
  • Series resistors’ combined resistance, parallel resistors simplification
  • Current and p.d. distribution in complex circuits
• High voltage (e.g., 230 V) can cause fatal electric shock
• Contact with bare wires or damaged insulation is risky
• Overheating due to excessive current can lead to fire or toxic fumes
• Damp or wet conditions increase the risk of electric shock
• Cables have specific maximum current ratings
• Insulation prevents contact and overheating
• Damaged insulation increases the risk of shock or fire
• Fuses prevent excessive current flow, protecting the system
• Increasing number of devices requires more sockets
• Multi-way bar extensions are safer than block adaptors
• Overloading sockets increases fire risk
• Fuse rating must match device requirements to avoid hazards
• Fuses prevent excessive currents to safeguard circuits and appliances
• Fuse wire melts at specific current values
• Correct fuse rating selection is crucial for protection
• Trip Switch breaks circuit when current exceeds a set threshold
• Used in modern house wiring systems for safety
• Earth wire provides low-resistance path to ground, preventing fatal shocks
• Mains circuit includes live, neutral, and earth wires
• Double insulated appliances eliminate the need for an earth wire
• Switches must be connected to the live wire to prevent fire or shock