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: R_Total = R₁ + R₂
  • In parallel: R_Total = 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 V_OUT), we use the following formula:
  • V_OUT = V_IN × (^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

Relay

• A switch operated by an electromagnet

Diode

• 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

Hazards

• 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