Electricity

• Charge


  It's the flow of electrical charge
• Current


  • Measured in amperes, amps (A)
  • Can be thought of as the rate of flow of charge
  • Measured using an ammeter
  • Can only be connected in a series
• Electrical charge


  Measured in Coulombs (C)
• Potential Difference


  • Causes electrical charges to flow
  • Measured in Volts (V)
  • Measured using a voltmeter
  • Can only be connected in a parallel
• Resistance


  • Slows down the flow of electrical charges
  • Measured in Ohms (Ω)
• Series Circuit


  • All components are in a single loop one after the other
  • The same flow of charge passes through each circuit component and so the current is the same in every component
  • The battery or cell provides the supply of p.d to the circuit
  • The p.d is shared between the other components
  • The total p.d is equal to the p.d of the battery
  • Resistance in a series adds up
• Parallel Circuit


  • Components are connected in separate loops
  • Each charge can only flow through one of the loops and so current is shared between loops
  • The p.d is the same in every loop
  • When resistors are connected, the supply current is shared between the resistors and so the overall resistance is reduced as the electrical charges may take many paths
• Mains Electricity


  In the UK, the mains electricity is an AC supply with a frequency of 50 Hz and p.d of 230V
• Direct Current (DC)


  Current flows in the same direction
• Alternating Current (AC)


  Current is constantly cycling between positive and negative directions
• Plug wires


  • Live Wire (brown) - Provides alternating p.d from the power supply
  • Neutral Wire (blue) - Completes the circuit back to the power supply, current flows through but p.d is 0
  • Earth Wire (green & yellow) - Stops the casing of the electrical appliance from carrying a current, only carries a current itself when there is a fault in the wiring
• Ohmic Resistors


  • If current and p.d are directly proportional (a straight line through the origin)
• Non-ohmic Resistors


  • The resistance of some resistors change depending on the current, because when the current increases, the wire gets hot and the metal atoms in the wire vibrate, causing more resistance
• Diodes


  • Allows current to flow one direction only
  • Above the maximum voltage, the resistance drops rapidly and the current increases rapidly
  • In the direction opposite to the allowed flow through the diode, resistance remains very high for all values of potential difference
• Current is measured in amperes (A) or amps.
• Electric charge is measured in coulombs (C).
• The current is the flow of electrons around a circuit.
• Potential Difference is measured in volts (V).
• Resistance is measured in ohms (Ω).
• Power is measured in watts (W).
• Ohm's Law states that the current flowing through an object is directly proportional to the potential difference across it if its temperature stays constant.
• Ohm's Law states that potential difference across a resistor is directly proportional to the current through it, provided its temperature remains constant.
• Increasing resistance increases potential difference and decreases current.
• Current = Potential Difference / Resistance
• Potential Difference = Current x Resistance
• A series circuit has only one pathway for electricity to travel along.
• Resistance = Potential Difference / Current
• In a parallel circuit there are multiple paths for the electric current to follow.
• When two or more components are connected together in a single loop they form a series circuit.
• Decreasing resistance decreases potential difference and increases current.
• The power dissipated by a component can be calculated using P = V x I or P = VI.
• The power dissipated by a component can be calculated using P = V * I or P = V^2/R
• Circuit Components :

  A) switch (closed)

  B) switch (open)

  C) Cell

  D) battery

  E) lamp

  F) fuse

  G) voltmeter

  H) ammeter

  I) diode

  J) LED

  K) Resistor

  L) variable resistor

  M) thermistor

  N) LDR

  
• National Grid


  System that transfers electricity using a high potential difference and a low current
• The National Grid needs to transfer a very large amount of energy
• Using a high current


  Wires would get very hot and a lot of energy would be lost to the surroundings as heat energy
• Efficiency


  It is cheaper and more efficient to use a very high potential difference (approximately 400000 V) and to keep the current very low
• Transformer


  • Made up of two coils: the primary and secondary coil
  • Coils are wrapped around an iron core
• Step-up transformer


  Transformer that increases the potential difference, with more turns on the secondary coil
• Step-down transformer


  Transformer that decreases the potential difference, with fewer turns on the secondary coil