Current, Potential Difference and Resistance

• 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 lamp.


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• Draw the circuit symbol for a fuse.


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• Draw the circuit symbol for a voltmeter.


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• Draw the circuit symbol for an ammeter.


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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 electric current?

  The rate of flow of charge through a wire or another component.
• State the equation linking charge, current and time.

  Give the units.

  Current (Amps/A) = Charge (Coulombs/C) / Time (seconds/s)

  I = Q / t
• What is the current like in a single closed loop / series circuit?


  Current is the same at every point in the circuit.
• What 2 factors does the current in a circuit depend on?

  • Potential Difference (V)
  • Resistance (R)
• State the equation linking voltage/potential difference, current and resistance.

  Give the units.

  Resistance (Ohms) = Voltage (Volts/V) / Current (Amps/A)

  R = V / I
• 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.
• In what 4 components is resistance not constant as current changes.

  • Lamps
  • Diodes
  • Thermistors
  • 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.
• What happens to the resistance of a thermistor as temperature increases?

  The thermistor's resistance decreases.
• Give 2 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.
• What happens to the resistance of a LDR as light intensity decreases?

  The LDR's resistance increases.
• When may an LDR be used?

  • Street lights.
  • When light levels become too low, the light gains sufficient current to turn on.
• What is used to measure current and potential difference/voltage?

  • Current - Ammeter
  • Potential difference/voltage - Voltmeter
• What is charge carried by?

  Electrons.
• What is resistance?


  Something that will restrict electrons' movement / make it difficult for them to get through.
• What is electrical resistance?


  • A measure of how difficult it is for electrons to move through a circuit.
  • As electrons move through the circuit, they collide with atoms in the wires, causing them to lose energy.
• What does a higher resistance mean?

  A lower current.