electricity

• circuit diagrams

  A) open switch

  B) closed switch

  C) cell

  D) battery

  E) diode

  F) resistor

  G) variable resistor

  H) LED

  I) bulb

  J) fuse

  K) voltmeter

  L) ammeter

  M) thermistor

  N) LDR

  
• current - electrical charge of flow, caused by potential difference

  potential difference - across a power source measures energy transferred to the charge and across the component measures energy transferred from the charge

  resistance - opposed the current
• parallel circuits:

  parallel - a circuit with more than one route for charge to flow

  • the total current of the circuit is the sum of the current on each path of the circuit/component
  • potential difference of each path is the same
  • the more resistors, resistance decreases. the total resistance is smaller than then the smallest resistance on a resistor
• LDR:

  • light dependent resistor
  • resistance changes as light intensity changes, -> to automatically turn on light when it gets dark
  • light intensity increases, resistance decreases
• thermistor:

  • resistance changes when temperature changes -> to turn on heating if temperature is too cold
  • as temperature increases, resistance decreases
• current:

  • direct current - flows in one direction e.g. batteries
  • alternating current - current constantly changes direction, backwards and forwards e.g. mains electricity
• series circuit:

  series - a circuit with only one route for charge to flow

  • current is the same at every point in the circuit/component
  • total potential difference of power supply is shared between components
  • the more resistors, the more resistance, the total resistance is the sum of all the resistors
• domestic electricity:

  • potential difference of mains electricity is 230v
  • frequency of current of mains electricity is 50Hz.
• plug:

  brown wire - live wire

  • carries alternating potential difference from the supply
  • 230v

  green and yellow wire - earth wire

  • safety wire to stop the appliance becoming live
  • only carries a current if there is a fault
  • 0v

  blue wire - neutral wire

  • completes the circuit
• national grid:

  power stations

  • generate electricity
  • 25kV

  step up transformer

  • increases p.d, lowers current
  • less energy is wasted as heat

  power lines

  • pylons and cables where it travels

  step down transformer

  • lowers p.d.
  • makes it safer for homes

  factories, homes, public places

  • 230v
• static electricity:

  • when certain insulators are rubbed against each other, they become electrically charged
  • negative electrons are rubbed off one material and given to the other
  • when two electrically charged objects are brought together, they exert a force on each other
  • opposite forces attract, same forces repel
  • example of a non contact force when they attract
• static electricity:

  polythene rod

  • rub with dry cloth
  • electrons from cloth transfer to rod making it negatively charged

  perspex rod

  • rub with dry cloth
  • electrons from rod transfer to cloth making it positively charged
• electric fields:

  • a charged object creates an electric field around itself
  • the electric field is stronger close to the charged object and weaker further from the charged object
  • a second charged object placed in the field creates a force
  • the force increases the closer the objects are brough together
• electric fields of the object

  the direction of the force exerted depends on the charge of the object