Topic 2 - Electricity

• Draw the circuit symbol for a cell.


  Diagram:

  
• Draw the circuit symbol for a battery.


  Diagram:

  
• Draw the circuit symbol for a lamp.


  Diagram:

  
• Draw the circuit symbol for a fuse.


  Diagram:

  
• Draw the circuit symbol for a voltmeter.


  Diagram:

  
• Draw the circuit symbol for an ammeter.


  Diagram:

  
• Draw the circuit symbol for a diode.


  Diagram:

  
• Draw the circuit symbol for a resistor.


  Diagram:

  
• Draw the circuit symbol for a thermistor.


  Diagram:

  
• Draw the circuit symbol for a variable resistor.


  Diagram:

  
• Draw the circuit symbol for an LDR (light dependent resistor).


  Diagram:

  
• Draw the circuit symbol for an LED (light emitting diode).


  Diagram:

  
• What is electric current?


  Flow of electric charge.
• State the equation linking charge, current and time.


  $Q =$$It$

  Charge (Coulombs) = Current (Amps) x Time (Seconds)
• 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?

  Voltage (Potential difference) and resistance.
• What equation should be used to calculate potential difference if current and resistance are known?


  $V =$$IR$ (Ohm's law)

  Potential difference (V) = Current (A) x Resistance (Ω)
• 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. LDRs
• What happens to the resistance of a filament lamp as the temperature increases? Why?


  Resistance increases therefore ions in metal have more energy so they vibrate more frequently, 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 example 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
  2. Parallel
• How does the potential difference across two components vary when connected in series and parallel?


  Series: Total potential difference is shared between each component.

  Parallel: Potential difference 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?


  The total resistance in a series circuit is equal to the sum of the individual resistances.
• Describe the current in a series circuit.


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


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


  In series
• How should you connect a voltmeter in a circuit to measure potential difference?


  In parallel
• Why is it advantageous to connect lamps in parallel?


  If one lamp blows, the rest will be unaffected and can still receive current.
• Is mains electricity an a.c supply or a d.c supply? What do they both stand for?


  a.c supply

  a.c = alternate current

  d.c = direct current
• Define a.c and d.c


  a.c = current that continuously changes direction at a specific frequency.

  d.c = one directional current flow.
• What is the frequency and voltage of the UK mains electricity supply?


  Frequency: 50 Hz Voltage: 230 V
• 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.


  Green and yellow stripes.
• State the insulation colour used on the live wire.


  Brown