(P2) ELECTRICITY

• v = ir

  Potential difference or voltage equals current times resistance
• As voltage increases

  Current increases proportionally
• As voltage decreases

  Current decreases proportionally
• Circuits with only wires or resistors

  • Resistance stays constant
  • Current vs potential difference graph is a straight line
• Bigger resistor


  Graph line is less steep
• Smaller resistor

  Graph line is steeper
• Higher currents can cause wires to heat up, so the lines don't always look perfectly straight
• Filament lamps

  • Contain a very thin metal filament
  • As current flows, filament heats up and resistance increases
  • Graph becomes less steep at higher voltages
• Diodes

  • Only allow current to flow in one direction
  • Have very high resistance in reverse direction
• Diodes only show current when potential difference is positive
• what is potential difference?

  a measure of energy transferred
• what is the potential difference also refered to?

  voltage
• what is potential difference measured in?

  volts
• what is resistance?


  a measure of how difficult it is for current to flow.
• The higher the resistance of a component, the harder it is for current to flow through the component.
• what is resistance measured in?

  ohms
• what is current measured in?

  amps
• what is The equation that links potential difference and current

  V = IR
• The current in a circuit is directly proportional to the potential difference across the power source of the circuit.

  For example, if the potential difference of a cell is doubled, the current will also double.
• The current passing through a component is inversely proportional to the resistance of the component.

  For example, if the resistance of a component doubles, the current passing through the component will halve.
• some resistors can be what?

  ohmic resistors
• what happens to the current when the resistance of an ohmic resistor changes?

  doesn't change
• The current through an ohmic conductor is directly proportional to the potential difference across the resistor.
• The current in a diode can only flow in one direction.
• why can the current in a diode can only flow in one direction?

  This is because they have a very high resistance in the reverse direction.
• what is a thermistor?

  a resistor that changes its resistance with temperature.
• what happens to the resistance of a thermistor at low temps?

  increases
• what happens to the resistance of a thermistor at high temps?

  decreases


  .
• give a use for thermistors

  temperature sensors or thermostats
• what is an LDR?

  light dependent resistor
• what does the resistance of an LDR depends on ?

  light intensity
• In low levels of light (low light intensity), the resistance is high.

  In high levels of light (brighter light), the resistance is low.
• give a use for LDR's

  circuits that automatically turn on lights at night
• A voltmeter should be connected in parallel (across und underneath) with the component it is measuring
• how do you measure current?


  with an ammeter
• An ammeter is connected in series (along the wire) with the component it is measuring.
• give the formula for resistance

  R = V/I
• What is a circuit?

  a closed loop that an electrical current can flow through
• If the components of the circuit are connected in a single loop, they are in series.
• If the components are connected using multiple loops(lines) , they are in parallel.