2. Electricity

• A build of electrostatic charge is caused by friction. When materials are rubbed, the electrons move. One material loses electrons to become positively charged and the other material gains electrons to become negatively charged.
• A build-up of electrostatic can cause a spark. If the potential difference is large enough, the electrons can jump across the gap (spark)
• Electric charges create an electric field. The closer you get to the object, the stronger the field. The electric field can be shown by drawing field lines
• Lines going in are for negative charges
• Lines going out are for positive charge
• Cell

  
• Resistor

  
• Battery

  
• Variable Resistor

  
• Open switch

  
• Closed switch

  
• Ammeter

  
• Voltmeter

  
• Bulb

  
• Diode

  
• Fuse

  
• LDR

  
• LED

  
• Thermistor

  
• Fixed resistor: current is directly proportional to the potential difference across the resistor.

  
• Filament Lamp: as the current increases so does the temperature. This makes it harder for the current to flow. The graph becomes less steep

  
• Diode: current only flows in one direction. The resistance is very high in the other direction which mean no current can flow

  
• LDR: Light Dependent Resistor, a resistor whose resistance decreases as light intensity increases. Uses of LDR's: street lights

  
• Thermistor: A thermistor is a resistor whose resistance decreases as its temperature increases. Uses of thermistors: Thermostats

  
• Series Circuit

  • Once one component is broken then all the components stop working
  • Voltage total = V1 + V2
  • Current1 = Current 2 = Current 3 (Amps)
  • Resistance total = R1 + R2

  
• Parallel circuits

  • These are more common, if one component stops then it will not affect the others. This means parallel circuits are more useful
  • Voltage 1 = Voltage 2
  • Total Current = i1 + i2 + i3
  • Resistance - adding resistance reduces the total resistance

  
• Electrical power is the rate of energy transferred. The amount of energy transferred is dependent on how long the appliance is in use for.
• The unit of power is Watts (W)
• AC - alternating current. Constantly changing direction - UK main supply is 230V and has a frequency of 50 hertz (Hz)
• DC - direct current. Supplied by batteries and flows in 1 direction
• Cables - most cables have three wires; live neutral and earth. They are covered in plastic insulation for safety
• Live wire - provides the potential difference from the mains.
• Neutral wire - completes the circuit and completes the circuit if there is a fault
• Earth wire - protection - carries a current is there is a fault
• The colour of live wire is blue, green or brown.
• The colour of the neutral wire is blue
• The colour of the earth wire is green with yellow stipes
• Electricity is transferred at a low current, but a high voltage so less energy is lost as it travels through long cables
• Step up transformers - increase potential difference and decrease the current
• Step down transformers - decrease the potential difference and increase current