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Electrical Circuits and Dangers of Electricity

Electrical Circuits
Circuit Diagrams

Series and Parallel Circuits
  • The current at any point in a series circuit is the same
  • The current splits at each branch in a parallel circuit so the total current is always greater than the current in one branch
  • Combining resistors
    • In series: RTotal = R1 + R2
    • In parallel: RTotal = 1/1/R1 + 1/R2
    • The combined resistance of 2 resistors in parallel is less than that of either resistor by itself
  • Advantages of putting lamps in parallel are;
    • If one lamp breaks, the other still works
    • Each lamp gets maximum p.d.
  • In series: P.d. across the supply = P.d. across all the components combined
  • In parallel: Current across the source = Sum of currents in the separate branches
Potential Divider
  • A potential divider divides voltage into smaller parts
  • To find the voltage (at VOUT), we use the following formula:
    • VOUT = VIN × (R2/RTotal)
  • A variable potential divider (potentiometer) is the same as the one above but using a variable resistor it acts like a potential divider, but you can change output voltage
Input Transducer
  • Thermistor: is an input sensor and a transducer. It is a temperature-dependent resistor. At a higher temperature, there is less resistance
  • Light Dependent Resistor (LDR): is an input sensor and a transducer. When light intensity increases, resistance decreases
  • A switch operated by an electromagnet

  • A diode is a device that has an extremely high resistance in one direction and a low resistance in the other direction, therefore it effectively only allows current to flow in one direction
  • Forward bias is when the diode is pointing in the direction of the conventional current, and reverse bias is the opposite
  • It can be used in a rectifier; it turns AC current into DC current
Digital Electronics
  • Analogue uses a whole range of continuous variations to transmit a signal
  • Digital signals use only 2 states, on and off
  • Logic gates are processors that are circuits containing transistors and other components
Dangers of Electricity
  • Damaged Insulation: Contact with the wire (live wire especially) due to a gap in the insulation causes an electric shock which can cause serious injury or shock
  • Overheating of Cables: When long extension leads are coiled up, they may overheat. The current warms the wire, but the heat has less area to escape from a tight bundle. This might cause a fire
  • Damp Conditions: Water can conduct a current, so if electrical equipment is wet and is touched, someone might get electrocuted

Benefits of Earthing a Metal case

  • Many electrical appliances have metal cases, the earth wire creates a safe route for current to flow through, if the live wire touches the casing
  • The earth terminal is connected to metal casing, so the current goes through earth wire instead of causing an electric shock
  • A strong current surges through the earth wire because it has very low resistance
  • This breaks the fuse and disconnects the appliance
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