Electrical Circuits

• This graph is the IV graph for current through a diode

  
• This graph is the IV graph for current through a filament lamp

  
• This graph is the IV graph for current through a ohmic conductor

  
• battery

  
• open switch

  
• closed switch

  
• cell

  
• diode

  
• resistor

  
• variable resistor

  
• LED

  
• lamp

  
• fuse

  
• thermistor

  
• LDR

  
• potential difference = current * resistance
• charge = current * time
• electrical energy = potential difference * charge
• In a thermistor, the resistance decreases as temperature increases
• In an LDR, the resistance decreases as light intensity increases
• LED stands for light emitting diode
• A diode is a component with a low resistance in the forward direction but a high resistance in the reverse direction
• current is the rate of flow of charge
• Transformers change the potential difference
• Step up transformers increase the potential difference and decrease the current. This makes the transfer of electricity via the pylons more efficient as a lower current would decrease the release of heat.
• A direct potential difference, also known as a DC potential difference, is a constant potential difference that always flows in the same direction. This type of potential difference is produced by direct current (DC) sources, such as batteries.
• Direct current is current that is always in the same direction
• A battery / cell gives a direct current / potential difference
• Explain the advantage of transmitting electricity at a very high potential difference in overhead power cables:

  • Very high p.d means low current
  • Which means less thermal energy is transferred to the surroundings
  • which increases the efficiency of power transmission
• A filament lamp's temperature increases when the current passing through it increases
• When the temperature of a filament lamp increases, the resistance increases
• As the light intensity decreases in an LDR , the potential difference across the LDR increases and the current in the LDR decreases. This is because the resistance has increased from the lower light intensity.
• Electricity in the UK is distributed across the country via the national grid
• The student becomes negatively charged because of the friction between his socks and the carpet.

  Explain why the friction causes the student to become charged.

  • Transfer of electrons
  • From the carpet to the student
• The negatively charged student touches a metal tap and receives an electric shock.

  Explain why.

  • There's a potential difference between the student and the tap
  • which causes electrons to transfer from the student to the tap
  • which earths the charge
• direct potential difference means the direction of the potential difference doesn't change
• As the current through the lamp increases, the filament gets hotter and has a higher resistance. The resistance of a filament lamp increase as the current through the filament increases and hence as the temperature increases.