electricity

• name the components:

  A) open switch

  B) closed switch

  C) cell

  D) battery

  E) diode

  F) resistor

  G) variable resistor

  H) light emitting diode

  I) lamp

  J) fuse

  K) voltmeter

  L) ammeter

  M) thermistor

  N) LDR

  
• current

  • flow of electrical charge
  • unit : ampere ( A )
  • measured using an ammeter
• series circuit:

  • no branches
  • current flows one path
  • current is the same all the way
  • voltage is distributed across all components
  • resistance: total resistance is the sum of all the resistors
• when the arrow is facing the positive terminal to the negative terminal its called the conventional current
• parallel circuits

  • have branches
  • current is split ( not equally )
  • voltage is the same across each branch
  • resistance : total resistance of the resistors is less than the resistance of the smallest resistor
• electrical charge

  • rate of electrical flow
  • 1 amp = 1 coulomb
  • measured in coulomb ( C )
• potential difference is directly proportional in an ohmic conductor
• resistance in a

  filament lamp

  A) bulb gets hotter

  
• diode

  • control the flow of current
  • curront only flows in one direction because theres high resistance in the reverse direction
• resistance in a diode

  A) no current in the reverse direction

  B) current in the forward direction

  
• LEDs

  • gives off light when current goes through
  • energy efficient
  • used for light bulbs , phone flash and computer screens
• light dependant resistors:

  • when its dark , the resistance is high
  • when its light, the resistance is low
  • uses: mobile phones and garden lamps
  • when its dark a higher resistance requires more potentional difference to pass through the ldr and the lamp recieves very little voltage so is very dim and the screen turns off
• thermistors:

  • temperature increase , resistance decreases
  • tempereature decrease , resistance increases
  • uses: thermostats and incubators
• resistance in ohmic conductors will stay constant if temperature stays constant
• potential difference

  • 1 volt = 1 joul
  • measured using a voltmeter
  • attached in parallel in a circuit
• resistance

  • the amount of potential difference required to drive the current through the component
  • units ohm - ( Ω )
• eg .blender and fans

  • transfer electrical energy into kinetic energy
  • low power rating
• eg. iron and kettle

  • transfer electrical energy into thermal energy
  • high power rating
• eg . hair dryer and washing machine

  • transfer electrical energy into kinetic energy and thermal energy
• power is the rate at which energy is transferred
• 1 watt = 1 joul per second
• dc

  • direct current
  • current from a cell
• ac

  • flow of electrons from the forward and reverse directions
  • from mains electricity
  • benefits : easy for a transformer to increase or decrease potential difference
• ac frequency - 50hz

  ac potential difference - 230v
• to see a pattern in the current use an oscilloscope
• three-core cable

  • wires made of copper because its a good electrical conductor
  • wires coated with plastic which cannot conduct electricity
• NEUTRAL wire:

  • blue wire
  • completed the circuit
  • pd: 0v
• EARTH wire

  • yellow and green stripes
  • connected to the earth/ground
  • use: when a live wire touches a metal case it becomes live with 230v , this is dangerous so the earth wire takes the current into the eart and the fuse melts to switch off the current
• the national grid is a system of transformers and high voltage cables
• a problem of the national grid is that energy is lost due to resistance
• a way to reduce energy loss is:

  • step-up transformers increase the potential difference to prevent energy loss
  • however its too high for homes so
  • step-down transformers reduce the potential difference to 230v
• static electricity is the transfer of electrons between insulators
• electrostatic charge can build up and spark triggering an explosion so areoplanes and trucks are earthed
• field lines for a positive charges

  arrows point outwards

  lines are perpendicular at 90' angles

  
• LIVE wire

  • brown wire
  • carries alternating potential difference
  • pd : 230v
  • connected to a fuse
  • dangerous and could be fatal if touched
• field lines for a negative charge

  arrows point inwards

  
• time interval for the current to change directions and change back again is 0.02 seconds

  there is one complete cycle

  to calculate frequency is $\frac{1}{time\ interval}$