Circuits

• Potential difference = Current x Resistance

  V = I x R
• Measure current by using an ammeter.
• Energy transfered = Potential difference x Charge

  E = V x Q
• Resistance:

  Anything that slows down the flow of charge around a circuit
• Variables that affect the size of a current:

  • Resistance
  • Potential Difference
• Electric current will increase when:

  • Number of ohms decreases.
  • Potential difference increases.
  • Resistance decreases.
• Ohmic conducter:

  A conducter that obeys Ohms Law.
• Conducter:

  Any electrical component which conducts electricity.
• Ohms Law:

  Potential difference = Current x Resistance
• • Resistance measured in Ohms (Ω)
  • Potential difference measured in Volts (V)
  • Current measured in Amperes (A)
  • Charge measured in Coulombs (C)
• Energy transfered = Power x Time

  E = P x t
• Increased light intensity to an LDR will decrease resistance.
• Diode:

  A component through which current can flow in only one direction.
• Resistor oposes flow of current.
• The National Grid is the network of cables and transformers that connect power stations with houses and shops in the United Kingdom.
• Properties of circuit breakers:

  • Switches off current.
  • Reusable.
  • Measures current.
• Potential difference:

  The difference between 2 points of a circuit , causes a current to flow
• Series circuit:

  A circuit with a single loop of wire
• Parallel circuit:

  A circuit with 2 or more loops of wire
• Current:

  Rate of flow of charge in a circuit
• Charge:

  Amount of electricity traveling through a circuit.
• Charge flow = Current x Time

  Q = I t
• The resistance of metal filament inside bulb increases as the potential difference increases because metals contain free electrons as temperature of filament lamp increases, ions vibrate faster.
• Live wire:

  Copper wire coated with brown plastic along which the current enters the device.
• Fuse:

  Glass or ceramic canister containing a thin wire that melts if current gets to high.
• Neutral wire:

  Copper wire coated with blue plastic that also connects to the cable in the wall and completes the circuit.
• Earth wire:

  Copper wire that is coated with striped plastic (yellow and green) that provides a path that for current to flow from the case of the device to the ground if there is a fault.
• National grid:

  Power station (25,000 V) --> Step-up transformer (Increases voltage, decreases current) --> Transmission cables (400,000 V) --> Step-down transformer (230 V, decreases voltage, increases current) --> Factory (33,000 V) --> Homes (230 V)
• Voltage is increased in step-up transformers to reduce energy lost due to heating.
• Voltage is decreased in step-down transformers to make it safe for consumer use.
• Energy transfered = charge flow x potential difference

  E = Q x V