Electricity

• Define current

  Flow of electric charge
• What is current measured in?

  Amperes (A)
• True or false: current has the same value at any point in a single closed loop

  True
• State the equation linking charge, current and time

  Charge = current x time
• What is charge measured in?

  Coloumbs
• What is time measured in?

  Seconds (s)
• State the symbol equation for charge, current and time

  Q = I x t
• What is an electrical insulator?

  A material that doesn't allow electric currents to pass through it
• Give two examples of an electrical insulator

  plastic and glass
• What is an electrical conductor?

  A material that allows electric current to pass through it?
• True or false: all metals are electric conductors

  True
• Explain how conductors (metals) conduct electricity (3 points)

  Conductors have lots of charges that are free to move

  In a metal these charges are delocalised electrons

  Electric current through the metal is the flow of these free electrons
• Explain why insulators do not conduct electricity (2 points)

  Insulators have no free electrons

  No charges are free to move and carry a current
• Define potential difference


  P.D is the difference in the amount of energy that charge carriers have between two points in a circuit
• What is potential difference measured in?

  Volts (V)
• What is another word for potential difference?

  Voltage
• How do we measure potential difference?

  Using a Voltmeter
• State the equation that links potential difference, current and resistance

  P.D = current x resistance
• State the equation that links voltage, charge and energy

  Voltage x Charge = Energy
• How do we measure current?

  Using an Ammeter
• How should an Ammeter be connected in a circuit?

  Connected in series (in the same loop of the circuit) with the electrical component whose current you're measuring
• How should a Voltmeter be connected in a circuit?

  Must always be connected in parallel with the two points being measured.
• What does a "factor of 5" mean?

  Multiply by 5
• Define resistance

  A measure of how difficult it is for current to flow through a component.
• What is resistance measured in?

  Ohms (horseshoe)
• State the symbol equation that links resistance, voltage and current

  R = V/I
• How do you measure the resistance of a component?

  Measure the P.D across the component
• What happens to the size of current if resistance increases?

  Size of current decreases
• What happens to the size of the current if P.D increases?

  Size of current increases
• What is an Ohmic conductor?

  A conductor that obeys Ohm's Law
• Explain "Constant Resistance" (2 points)

  The current through an ohmic conductor (at a constant temperature) is directly proportional.

  This means that the resistance remains constant as the current changes
• State the equation that links P.D, resistance and current.

  P.D = Resistance x current
• Describe a current voltage graph for a Resistor

  A straight line (constant resistance)

  
• Describe a current voltage graph for a filament lamp

  Curved line as the current through lamp increases so does the temperature which increases the resistance of the lamp.

  
• What is a Diode?

  A component that only allows a current to flow through it in one direction.
• Why does a Diode act as a rectifier?

  They block an alternating current when it changes direction
• What is a thermistor?

  A component whose resistance changes with its temperature. (e.g inc temp = dec resistance)
• Give one use of a thermistor

  Turn a heater off when a house reaches certain temperature
• Describe the resistance in a light dependent resistor (LDR)?


  Usually, increasing light intensity decreases the resistance.
• Give two uses of an LDR

  Switch lights on when it gets too dark

  To know whether a phone camera needs to use the flash