Electricity

• Draw the circuit symbol for a cell


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• Draw the circuit symbol for a battery

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• Draw the circuit symbol for a fuse.

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• Draw the circuit symbol for a diode.

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• Draw the circuit symbol for a resistor.

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• Draw the circuit symbol for a thermistor.

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• Draw the circuit symbol for a variable resistor.

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• Draw the circuit symbol for an LDR


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• Draw the circuit symbol for an LED.


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• What is a electric current

  The flow of electrical charge
• What can be said about the value of current at any point in a single closed loop?

  Current is the same at all points in a closed loop.
• What two factors does the current in a circuit depend on?

  1. Potential Difference (V)
  2. Resistance (R)
• What is an ‘Ohmic Conductor’? State the condition required.

  ● A conductor for which current and potential difference are directly proportional

  ● Resistance remains constant as current changes

  ● Temperature must be constant
• List four components for which resistance is not constant as current changes.

  1. Lamps
  2. Diodes
  3. Thermistors
  4. Light Dependant Resistors (LDRs)
• What happens to the resistance of a filament lamp as the temperature increases? Why?

  ● Resistance 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
• What is different about current flow through a diode?

  ● The current only flows in one direction

  ● Resistance is very high in the other direction, preventing current flow
• State what happens to the resistance of a thermistor as temperature increases.

  The thermistor’s resistance decreases.
• Give two examples of when a thermistor may be used.

  1. In a thermostat to turn a heater on below a certain temperature
  2. In a freezer to turn on a cooler when the temperature becomes too high
• State what happens to the resistance of a LDR as light intensity decreases.

  The LDR’s resistance increases.
• Give an application for a LDR.

  ● Street lights often use LDRs

  ● When light levels become too low, the light gains sufficient current to turn on
• What are the two ways that a component can be connected in a circuit?

  1. Series (same loop)
  2. Parallel (adjacent loop)
• How does the potential difference across two components vary when connected in series and parallel?

  ● Series: Total P.D is shared between each component

  ● Parallel: P.D across each component is the same
• If two resistors are connected in parallel, what can be said about their combined total resistance?

  Their total resistance is less than the smallest of the two individual resistances.
• If two resistors are connected in series, what can be said about their total resistance?

  Their total combined resistance is equal to the sum of the two individual resistances.
• Describe the current in the series

  In a series circuit, the current is the same at all positions since the charge only has one path to flow through
• In a series circuit, the current is the same at all positions since the charge only has one path to flow through


  In a parallel circuit, the current is shared between the different branches. When the charge reaches a junction it splits.
• How should you connect an ammeter in a circuit to measure current?

  Ammeters should be connected in series with the component that they are measuring current through.
• How should you connect a voltmeter in a circuit to measure potential difference?

  Voltmeters should be connected in parallel to the component that they are measuring the potential difference of.
• Why is it advantageous to connect lamps in parallel?

  If one lamp blows, the rest will be unaffected and can still receive current (i.e. the circuit is still complete).
• Is mains electricity an a.c supply or a d.c supply? What do each of these stand for?

  Mains electricity is an AC supply
• Whats the frequency and voltage of the UK mains electricity supply?

  ● Frequency: 50 Hz

  ● Voltage: 230V
• How many wires are usually in the cables connecting electrical appliances to the mains? Name these wires.

  1. Live wire
  2. Neutral wire
  3. Earth wire
• State the insulation colour used on the Earth wire.

  Yellow and green stripes
• State the insulation colour used on the live wire.

  Brown
• State the insulation colour used on the neutral wire

  Blue
• Explain when the earth wire does and doesn't carry a current

  • Under normal circumstances, no current flows through the Earth wire ● If a fault occurs in the appliance (such as a surge or the casing becoming live), current will flow to the ground
• What potential is the neutral wire at?

  0 volts
• State the potential difference between the live and earth wires.

  230 volts
• What is the purpose of the neutral wire?

  Safety

  To complete the circuit by connecting the appliance back to the mains supply.
• For metal appliances, where is the Earth wire connected to? Why?

  ● Earth wire is connected to the metal casing of the appliance

  ● If live wire becomes loose and touches the casing, the current will flow through the Earth wire, preventing electrocution