Electricity- physics

• Draw the circuit symbol for a lamp
• Draw the circuit symbol for an LDR
• Draw the circuit symbol for a voltmeter
• Draw the circuit symbol for a diode
• Draw the circuit symbol for a battery
• Draw the circuit symbol for a fuse
• Draw the circuit symbol for a cell
• Draw the circuit symbol for a variable resistor
• Draw the circuit symbol for a resistor
• Draw the circuit symbol for a thermistor
• Draw the circuit symbol for an ammeter
• Draw the circuit symbol for an LED
• State the equation linking charge, current and time. Give the units for the quantities involved.
• List four components for which resistance is not constant as current changes.
• What can be said about the value of current at any point in a single closed loop?
• What is electric current?
• Current is the same at all points in a closed loop
• What is an ‘Ohmic Conductor’? State the condition required.
• Factors the current in a circuit depends on

  • Potential Difference (V), Resistance (R)
• Units for the quantities involved in the equation V = I R

  • Potential Difference (V), Current (A), Resistance (Ω)
• Units for the quantities involved in the equation Q = I t

  • Charge (Coulombs), Current (Amperes), Time (Seconds)
• Characteristics of an Ohmic Conductor

  • A conductor for which current and potential difference are directly proportional
  • Resistance remains constant as current changes
  • Temperature must be constant
• Components for which resistance is not constant as current changes

  • Lamps
  • Diodes
  • Thermistors
  • Light Dependant Resistors (LDRs)
• What equation should be used to calculate potential difference if current and resistance are known? State the units for all 3 quantities.
• Resistance of a LDR increases as light intensity decreases
• Components for which resistance is not constant as current changes

  • Lamps
  • Diodes
  • Thermistors
  • Light Dependant Resistors (LDRs)
• Current flow through a diode only flows in one direction
• Examples of when a thermistor may be used

  • In a thermostat to turn a heater on below a certain temperature
  • In a freezer to turn on a cooler when the temperature becomes too high
• Resistance of a filament lamp increases as the temperature increases


  Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow
• Application for a LDR

  • Street lights often use LDRs
  • When light levels become too low, the light gains sufficient current to turn on
• Resistance of a filament lamp increases as the temperature increases
• Current flow through a diode

  Resistance is very high in the other direction, preventing current flow