Physics - Electricity

• What is current?


  Current is the rate of flow of charge around the circuit.
• What is Voltage/Potential Difference?

  Voltage/Potential Difference is what drives the current around the circuit. It is like an "electrical pressure".
• What is resistance? 


  Resistance is what slows down the current in a circuit
• Increasing the voltage will cause more current to flow.

  Increasing the resistance will cause less current to flow.
• What does the Ammeter do?

  • Measures the current (in amps) flowing through the component.
  • Must be placed in series anywhere in the circuit, but never in parallel like the voltmeter.
• What does the Voltmeter do?

  • Measures the voltage (in volts) across the component.
  • Must be placed in parallel around the component being tested, never around the variable resistor or the battery.
• Ammeter and Variable Resistor has to be placed anywhere in series.

  Voltmeter has to be placed in parallel to the component being tested.
• • Mains Supply is Alternating Current, with an approximate voltage of 230V. Alternating Current means that it constantly changes direction.
  • Battery Supply is Direct Current, Which means that it is constantly flowing in the same direction.
• Formula linking Voltage, Current and Resistance. 


  Voltage = Current X Resistance.
• Which component is this Current-Voltage graph for?

  The Wire

  
• Which component is this Current-Voltage graph for?

  The Diode

  
• Which Component is this Current-Voltage graph for?

  The Metal Filament Lamp

  • As the temp of the component increases,, So does the resistance, hence the curve.

  
• What Component is this Current-Voltage graph for?

  Different Resistors.

  
• A Light-Dependent Resistor is a special type of resistor that changes its resistance depending on how much light falls on it.

  • More Light = Less Resistance
  • Less Light = More Resistance
• A thermistor is a temperature-dependent resistor.

  • Hotter Temp = Less Resistance
  • Colder Temp = More Resistance
• Series Circuit

  • Connected in a line, end to end, between the +ve and the -ve of the power supply.
  • If you remove or disconnect one component, the circuit is broken and they all stop working.
• Series Circuit

  • Bigger potential difference when more cells are in series.
  • Current is the same everywhere.
  • The Potential Difference is Shared.
  • The Size of the current depends on the total potential difference and the total resistance of the circuit.
• Parallel Circuits

  • removing or disconnecting one component will hardly affect the others.
  • Current is shared.
  • Potential Different is the same everywhere.
  • Total current entering a junction equals to the total current leaving it.
  • The total resistance of the circuit decreases if you add a second resistor in parallel.
• Parallel Circuits

  • Current is Shared
  • Potential Difference is the same everywhere

  Series Circuits

  • Current is the same everywhere
  • Potential Difference is shared
• Formula for Charge


  Charge = Current X Time
• Formula for Energy Transferred

  Energy Transferred(J) = Charge(Q) X Voltage(V)
• Formula for Energy Transferred including Current and Resistance

  Energy Transferred(J) = Charge(Q) X Current(I) X Resistance(R)
• 3 Wires in a plug

  • The live and neutral wires are usually needed. But the Earth Wire stops you getting hurt.

  Live Wire (Brown)

  • Alternates between a high +ve and -ve voltage of about 230V
  • Electricity normally flows in through the live wire.

  Neutral Wire (Blue)

  • Electricity normally flows in through the neutral wire.

  Earth Wire (Yellow/Green)

  • The Earth Wire is used to Earth an strong electrical current in order to prevent electric shocks and fires.
• What does Fuses and Earthings do?

  They prevent Fires and Shocks
• Formula for Electrical Power

  Electrical Power = Current X Voltage
• Units :

  • Amps = Current
  • Coulomb = Charge
  • Joule = Energy
  • Ohm = Resistance
  • Seconds = Time
  • Volts = Voltage
  • Watt = Power
• Safety Precautions in a plug :

  • Insulation - Insulated by an insulator
  • Double Insulation - Insulated by 2 layers
  • Earthing - Using the earth wire to transfer big surge to the earth, This big surge also activates a big surge to go through the live wire causing the fuse to break.
  • Fuses and Circuit Breakers - Stop shocks and fires from happening by not completing the circuit
• Electric current in solid metallic conductors is a flow of negatively charged electrons