Electric Circuits

• What is a series circuit?

  A circuit where the components are connected in a single path, allowing the flow of current through each component one after another.
• What is a parallel circuit?

  A circuit with multiple paths for current to flow.
• What is used to measure the current?

  An Ammeter.
• What is used to measure the voltage?

  A voltmeter.
• Resistors


  Used to control or change the current
• Types of resistors


  • Fixed resistors
  • Variable resistors
  • Thermistors
  • LDRs (light dependent resistors)
• Fixed resistors


  • Used to lower the current
• Variable resistors, thermistors, LDRs

  • Can change their resistance and change the current
• Variable resistors


  Can be changed by moving a slider or turning a dial, e.g. dimmer switch
• Thermistors


  Change resistance depending on the temperature; higher temperature = lower resistance
• LDRs


  Change resistance depending on the light on the LDR; brighter light = lower resistance
• Drawing a circuit


  1. Draw the correct symbols in place first

  2. Connect using straight lines to represent the wires
• Power of a circuit

  Represents the energy transferred per second, measured in Watts where 1W = 1 Joule per second
• Equations to calculate power

  • Power(W) = Voltage(V) × Current(A)
  • Power(W) = Current(A)2 × Resistance(Ω)
  • Energy(J) = Power(W) × Time(s)
• Investigating how current changes with voltage for a bulb

  1. Connect circuit with variable resistor

  2. Record current and voltage

  3. Adjust variable resistor and take next set of results

  4. Repeat until complete set of results
• Ammeter


  Measures current, must be connected in series
• Voltmeter


  Measures voltage, must be connected in parallel
• Series circuits

  Resistance increases according to R = R1 + R2
• Parallel circuits

  Resistance of the circuit decreases according to 1/R = 1/R1 + 1/R2
• Electrical component symbols


  • switch
  • LDR
  • cell or battery
  • a.c. power supply
  • diode
  • d.c. power supply
  • resistor
  • variable d.c. power supply
  • variable resistor
  • lamp
  • fuse
  • ammeter
  • voltmeter
  • thermistor
  • LED
• Resistor or wire (at constant temperature)

  Constant resistance
• Filament lamp

  Resistance increases at higher voltages
• Diode


  Very high resistance (no current) until a specific voltage
• You must learn the shape of the current-voltage curve for each device and be able to describe why it is that shape
• Series circuits

  • Equal current everywhere in the circuit
  • Voltage is shared between the components but must add to the voltage from the power source
• Parallel circuits

  • Current is shared between the components but must add to the current from the power source
  • Equal voltage across each component