Electricity

• To draw more complex circuits, knowledge of symbols for different components and their placement is required
• What is an electrical circuit

  A closed loop that contains a power source (e.g., a cell) and something for the electrons to flow through (e.g., a wire)
• Electrical circuits are generally represented with circuit diagrams
• Cells and batteries act in the same way in circuits
• Common symbols in circuit diagrams

  • Cell
  • Battery
  • Filament lamp
  • Switch
• A simple electrical circuit consists of a power source (e.g., a cell) and a wire for electrons to flow through
• Batteries are made up of two or more cells, and their symbol is two cell symbols put together
• Current


  A measure of the flow of electrons around the circuit, similar to the flow of water through a pipe, measured in amperes (amps)
• Potential difference (Voltage)


  The force driving the flow of electrons, provided by the cell or battery, measured in volts
• Resistance

  Everything that resists or opposes the flow of electrons, measured in ohms
• Conventional current flows from

  Positive terminal to negative terminal
• Electrons flow from

  Negative terminal to positive terminal
• Diodes only allow current to flow in one direction
• For different resistors, the line on the graph would be more or less steep
• Temperature staying constant is assumed for the analysis
• Temperature and resistance affect the behavior of filament lamps and diodes
• V equals IR is the most important equation in the electricity topic
• Higher currents generally cause wires to heat up
• As potential difference increases

  Current in the circuit also increases
• Filament lamps contain a thin metal filament that emits light as it heats up
• Relationship between voltage, current, and resistance

  As long as resistance stays constant, increasing voltage increases current proportionally or vice versa
• Lines in circuits containing only wires or resistors are straight due to constant resistance
• Effect of temperature on resistance

  If temperature increases, resistance also increases
• V equals IR

  Potential difference or voltage equals current times resistance
• Diodes have high resistance in the reverse direction to prevent current flow
• Graphs of filament lamps and diodes show different behaviors
• Smaller resistors require less potential difference to drive a large current
• Heat in filament lamps increases resistance, causing the curve to be less steep at higher currents
• Cell or battery is needed to provide electric power to a circuit


  Switch controls the flow of electricity by being either closed (allowing electricity to flow) or open (turning off the circuit)
• Light emitting diodes (LEDs)


  Emit light when current flows through in the forward direction
• Fuses


  Break if too much current flows through the circuit
• Thermistors

  Resistance is dependent on the temperature, with higher temperatures causing the resistance to fall and lower temperatures increasing the resistance
• Voltmeters


  Measure potential difference and are added in parallel
• Resistors


  Can be fixed to provide a certain number of ohms worth of resistance or can be variable to modify the amount of resistance they provide
• Main components needed to provide electric power to a circuit

  • Cell
  • Battery
  • Switch
  • Filament lamps
  • Fuses
  • Diodes
  • Light emitting diodes (LEDs)
  • Ammeters
  • Voltmeters
  • Resistors
  • Light dependent resistors (LDRs)
  • Thermistors
• Drawing circuit diagrams

  Requires knowledge of different components and their functions, as well as the symbols used to represent them
• Light dependent resistors (LDRs)


  Resistance is dependent on the intensity of light, with low resistance in bright light environments and high resistance in darkness
• Ammeters


  Measure current and are connected in series
• Diodes


  Only allow current to flow in one direction
• Thermistors are used as temperature receptors in things like car engines and electronic thermostats