P3 - ELECTRICITY

• what is charging by friction?

  when certain insulating materials are rubbed against each other they become electrically charged
• attraction

  objects get closer together
• repulsive

  objects move further apart
• if charges are opposite, they will____

  attract
• if charges are the same, they will_____

  repel
• common electrostatic phenomena?

  shocks from everyday objects

  lightning

  charged balloon sticking to wall
• how does a static electric spark occur?

  1. 2 objects are charged by friction
  2. they become oppositely charged
  3. large surplus of electrons causes electrons to jump across to an object that is neutral
• what is an electric field?

  a region where an electric charge experiences a force
• • Fields lines always point away from positive charges and towards negative charges
• how can you represent a weak field?

  field lines further apart
• Electric current is defined as the rate of flow charge
• how to measure current?

  using an ammeter

  connected in series with the part of the circuit you wish to measure
• current = charge / time
• sources of potential difference?

  a cell, batteries, electrical generator
• in a closed loop circuit (e.g. series), current is the same at any point.

  • all components have the same current
• common circuit symbols

  A) open

  B) closed

  C) fixed resistor

  D) variable resistor

  E) thermistor

  F) ldr

  G) diode

  H) LED

  I) motor

  J) ammeter

  K) voltmeter

  
• what does a resistor do?

  limits the flow of electric current.
• what is a thermistor?

  Temperature-sensitive resistor.
• what is a diode?

  allows current to flow in one direction only

  convert AC to DC current
• a voltmeter is always connected in?

  parallel
• an ammeter is always connected in?

  series
• what is the direction of current flow?

  positive terminal to negative terminal
• the higher the resistance the ____ the current


  lower
• potential difference = current x resistance
• 2 types of resistors?

  fixed and variable
• as the temperature increases, the resistance of a thermistor _____ ?

  decreases
• as the light intensity on an LDR increases, the resistance decreases
• • Fixed resistors have a resistance that remains constant
  • Variable resistors can change the resistance by changing the length of wire that makes up the circuit
  • A longer length of wire has more resistance than a shorter length of wire
• what components have linear I-V characteristics?

  fixed resistors, wires, heating elements
• components with non linear I-V characteristics?

  filament lamps, diodes, LED, LDR and thermistors
• what components is this for?

  A) diode

  
• what components is this graph for?

  A) filament lamp

  
• what type of circuit is this

  A) series

  
• what type of circuit is this

  A) parallel

  
• in a parallel circuit,

  • If one component stops working the others will continue to function
  • The components can be individually controlled, using their own switches
  •  the current splits up
• in series, the individual resistances add up to get the total resistance.

  the individual voltages also add up to get the total voltage.
• Current in Series & Parallel

  • In a series circuit, the current is the same at all points
  • In a parallel circuit, the current splits at junctions – some of it going one way and the rest going the other
• Potential Difference in Series & Parallel

  • In a series circuit, the voltage of the power supply is shared between the components
  • In a parallel circuit, the voltage across each component is the same
• what does power depend on?

  voltage and current
• power = current x voltage