Physics Topic 2: Electricity

• what is an voltmeter?


  meauses the potential difference (volts)
• what is an ammeter?

  meausres the current (the amps)
• what is resistance?


  opposition to current flow
• formula for energy?


  energy (j)=charge(c) x voltage
• state the formula for resistance

  potential differents (volts)/current(amps)
• formula for charge flow

  Charge flow = current x time
• why are metals good conductors of electricity

  outer electrons are not attatched to any particular atom, they are free to move between the atoms

  
  

  when the metals are heated the free electrons gain kinetic energy, move faster and travel through the gaps between the ions
• what happens in series circuits?

  current stays the same through each component

  the potential difference is shared

  total resistance of the two components is the sum of resistance of each component

  total reistsance= r1+r2
• why does adding resistors in series circutis increase the total resistance

  in a series circuit the current is the same everywhere so the total current in a circuit is reduced when a resistor is added

  
  

  so the total resistance of the circuit increases
• what does ac and dc stand for

  Alternating current and direct current
• what factors affect the rate of resistance

  how long the wire is

  how thick the wire is

  how many components

  how hot the wire is
• formula for voltage and potential difference


  current x resistance
• state the equation for power

  current^2 x resistance
• give the equation for charge flow

  Charge flow = current x time
• what is meant by zero erorr?

  ammeater is displaying a reading when not connected
• define an alternating current and describe its graph

  an alternating current regurlary changes direction

  
• in the uk what frequency is mains electrical supply

  50hz
• what is potential difference

  Voltage - is the driving force that pushes the electric charge around the circuit
• define resistance (ohm)


  The opposition of current flow.
• what does a current flowing through a component depend on?

  the potential difference and the resistance of the component
• the greater the resistance accros a component


  the smaller the current that flows through it
• define current


  The rate of flow of charge
• from where does current flow

  positive to the negative
• charge=


  current (a) x time (s)
• potential difference (v)=


  current (A) x resistance (ohms)
• whats ohms law


  V=IR
• describe the I-V CHARECTRISTIC GRAPH for a ohmic conductor

  directly proportional
• describe the graph for a filament lamp

  as the current increases the temp of filament increases, so resistance increases
• describe the graph for a diode

  only flow from one direction, high resistance
• whats a thermisstor


  temperature dependent resistor

  when its hot resistance drops

  when its cool resistance increases

  useful for central heating or car engines
• whats ldr


  Light dependent resistor

  dependent on intensitiy of the light

  
  

  bright light=resistance falls

  darkness= resistances highest

  
  

  useful for outdoorlighting and burgalar detectors
• features of series circuits

  total pd is shared

  current is the same everywhere

  resistance adds up
• features of a parallel circuit
• What is alternating current


  Current that is CONSTANTLY changing direction
• What is direct current?

  movement of charge in one direction only
• Whats the frequency of the uks mains supply

  50hz and 230V
• What are the chords in a cable made out of?

  Copper
• Why copper?


  Can conduct electricity and is cheap
• What is the copper wire coated with

  Insulating layer of plastic for saftey
• What colour is the live wire

  brown