P3

• Circuits


  • Something for electrons to flow through
  • Closed loop
• Current (I)


  A measure of flow of electrons around the circuit, measured in Amps (A)
• Potential difference (voltage) (V)

  The force driving the flow of electrons,

  • provided by cell or battery
  • measured in volts
• Resistance (R)


  Everything that resists or opposes the flow of elections, measured in ohms
• Electrons are negatively charged so flow from negative to positive in a circuit
• Conventional current is said to flow from positive to negative
• Static Electricity


  Build up of charge on insulating materials
• All materials contain charge, but most are neutral as positive and negative charges cancel each other out
• Friction causes electrons to move from one object to another

  1. In conducting materials (e.g. metal)

  • electrons are able to move

  
  

  2. In insulating materials

  • electrons can't flow back
  • positive static charge occurs on material that loses electrons
  • negative static charge occurs on material that gains electrons
• Electron transfer depends on specific materials

  only negative electrons are being transferred
• As the size of the static charge increases

  A potential difference is induced between the charged material and any earth object
• If the potential difference is large enough, electrons can jump between the objects, which is a spark
• Static charge can build up due to contact with the wind
• What kind of graph is this for

  • Wire and resistor
  • Less resistance, steeper the line
  • Directly proportional

  
• What graph does this represent?

  • Filament lamp
  • Increasing current increases temperature which makes resistance increase
  • so I-V graph is curved

  
• What graph does this represent?

  • Diode
  • Current flows in one direction
  • High resistance in opposite direction

  
• Resistance increases with temperature

  • electrons flow through resistor, some energy transferred to thermal energy store- heating it up
  • causes particles to vibrate more, making it harder for charge-carrying electrons to pass through resistor
  • More current means an increase in temperature= increase in resistance so current decreases again
  • Henry why filament lamp levels off
• Charge- measure of total current within a period of time

  $Q =$$IT$

  Q- coulombs

  I= Amps

  T= seconds
• $V =$$IR$

  V= P.D (Volts)

  I= charge (amps)

  R= resistance (ohms)
• Series circuit 


  > Components all connected

  > Whole circuit will stop working if one thing breaks

  p.d- shared across

  Current- save everywhere

  Resistance- sum of resistance everywhere

  > Components with greatest resistance have highest current
• Parallel circuit 


  > More than one loop

  > Each loop contains a component- efficient if component breaks it doesn't effect circuit

  p.d- same everywhere

  current- sum of all components - greater resistance less current

  resistance- more components/loops, lower total resistance
• Cell

  
• Battery

  
• Filament lamp

  
• Fuse

  
• Light emitting diode

  > light emits as current flows through it

  > current flows one way

  
• Diode

  > allows current to flow in one direction

  
• variable resistor

  > modify amount of resistance

  
• Fixed resistor

  
• Light dependent resistor (LDR) - A resistor whose resistance decreases as light intensity increases.

  
• Thermistor

  > dependent on temperature

  > Hot causes resistance to fall \

  
• Ammeter

  > Measures current

  > Added in series
• Volt meter

  > measures p.d

  > added in parallel
• 3 energy calculations


  Energy = Power x time $E=$$Pt$

  Energy= Voltage x Current x time $E=$$VIt$

  Energy= Charge x voltage $E=$$QV$
• Energy with power and time 


  Energy = Power x time
• Energy with current, time and p.d

  Energy = Voltage x current x time
• Energy with charge and voltage

  Energy= Charge x voltage
• Power with voltage and current

  Power = Current (I) x Voltage (V)
• Power with Voltage and resistance


  Power = Current$^2$x resistance
• AC

  • alternating current
  • Fluctuates between positive and negative
  • perpendicular direction