SP10/11

• what is current?

  Flow of electric charge.
• what is the equation for flow of charge?

  Charge (C) = current (A) x time (s)
• a current has the same value at every point in a single closed loop.
• what is an electrical conductor?

  a material that allows electric currents (flow of electric charges) to pass through it.
• what are examples of an electric conductor?

  all metals
• what is potential difference (voltage)?

  the driving force that pushes the charge round.
• what units is potential difference measured in?

  volts (V)
• what is the equation for potential difference (voltage)?

  voltage = energy transferred / charge
• what is the potential difference of 1 volt equal to?

  1 joule per coulomb
• what do ammeters measure?

  the flow of current that passes through it.
• ammeters have to be connected in series (in the same loop of the circuit) with the electrical component whose current you are measuring.
• what do voltmeters measure?

  the potential difference (voltage) between the 2 points in a circuit.
• voltmeters must always be connected in parallel (on a seperate branch of the circuit) with the 2 points being measured.
• how is current measured?

  through a component.
• how is potential difference measured?

  between 2 points either side of a component.
• when a charge flows in an electric circuit, what 2 factors affect the size of the current?

  • resistance: if the resistance increases, the current decreases.
  • potential difference: if potential difference increases, the current will increase.
• what is resistance measured in?

  ohms
• what is resistance?

  a measure of how difficult it is for current to flow through a component.
• what is the equation for resistance?

  resistance = potential difference / current
• the longer the wire, the higher the resistance.
• the current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the the resistor.
• the resistance remains constant as the current changes.
• what is a conductor?

  any electrical component which conducts electricity.
• what is an electrical insulator?

  a material that doesn't allow electric currents to pass through it.
• what are examples of electrical insulators?

  plastic and glass
• why do electrical insulators not conduct electricity?

  they have no free electrons and so there are no charges free to move and carry a current.
• why do electrical conductors conduct electricity?

  they have lots of charges that are free to move. In a metal, the charges that are free to move are electrons. The electrical current through the metal is the flow of these free electrons.
• what is the equation for voltage?

  voltage = energy / charge
• what is the equation for resistance?

  resistance = potential difference / current
• what do you need to do in order to measure the resistance of a component?

  measure the potential difference across the component.
• resistance remains constant as the current changes.
• how does the size of a wire affect resistance?

  • increasing the length increases resistance.
  • decreasing the cross-sectional area of the wire increases resistance.
  • short, wide wires have less resistance than long, narrow wires.
• what is resistance proportional to?

  the length of the wire divided by the cross-sectional area.
• on a current/voltage graph for a resistor, what is the slope of the graph equal to?

  1 / resistance
• what happens to the gradient of a current-voltage graph at a larger potential difference?

  decreases
• in a current-resistance graph, what does a constant slope tell us?

  the resistance is constant.
• where does charge flow from?

  the energy source and through the rest of the circuit and its components, like lamps and heaters.
• what does the flow of current transfer?

  the energy from the energy source to the components.
• what are the equations for power?

  • power = current x potential difference
  • power = (current)^2 x resistance
  • power = energy / time
• why is some of the kinetic energy of electrons moving through the resistor is transferred to heat energy?

  due to collisions between the electrons and the ions present in the resistor.