Friday test

• Circuit diagrams


  An electric map showing the path through which electric charges can flow
• A circuit should be constructed in an unknown long
• Series connection


  Components connected one after the other
• Series connection


  • Single path for current
  • If switch opens - all components switch off
  • If component breaks - no current flows
• Parallel connection


  More than one path for current
• Parallel connection


  • Current divides
  • If one component breaks - others will continue
• Potential difference across the ends of a conductor is the force that causes charge to flow through it
• Potential difference


  Unit is the volt
• Potential difference causes electric charge to move from a region of high energy to a region of low energy
• 1 volt is equivalent to 1 joule per coulomb
• EMF


  Electromotive force
• Emf


  • The work done per unit charge by the source (battery)
  • The maximum amount of energy transferred to each unit of charge that moves between its terminals
  • The voltage measured when no current is flowing through the battery
• Voltmeter


  • Has a very high resistance and is always connected in parallel
  • Uses a small amount of current that makes no noticeable difference to the current in the main circuit
• Terminal potential difference


  • The voltage measured across the terminals of a battery when charges are flowing in the circuit
  • Usually less than the emf because some energy is required to move charge through the battery
• Current strength


  • The rate of flow of charge
  • Measured in Amperes (A) which is the same as Coulomb per second
  • The rate at which electrons are flowing in an electric circuit
• When the switch is open, the terminal potential difference is 5V
• V=W/q

  V=Potential Difference(V)

  W=energy/heat(J)

  q=charges(C)
• Current direction


  The direction a positive charge would move if placed in an electric field
• Current direction


  Opposite to the flow of electrons (since electrons are negatively charged)
• Calculating current


  1. Current = charge passing a point / time

  2. Current = Q / t
• Q


  Charge (C)
• I


  Current (A)
• t


  Time (s)
• Ammeter


  Device used to measure current
• Ammeter


  • Has a very low resistance
  • Always connected in series
• Purpose of ammeter

  Ensures current can flow through it to be measured accurately
• Ammeter


  • A
• Resistance


  The opposition to the flow of current
• Factors that affect resistance


  • Type of material
  • Length
  • Thickness
  • Temperature
• Components with high resistance


  Use up the energy that the battery gives the charge carriers and transfers it to a different form of energy
• The higher the resistance in a circuit


  The lower the current will be
• Resistance


  The ratio of the potential difference across a resistor to the current in the resistor
• Resistance


  • Insulator = more resistance
  • Longer material = more resistance
  • Thinner material = more resistance
  • Hotter temperature = more resistance
• Ohm's Law


  The current across a conductor is directly proportional to the potential difference across the conductor at a constant temperature
• Unit of resistance


  One Ohm (Ω) is equal to one volt per ampere
• OHMIC


  Conductors that obey Ohm's law
• NON-OHMIC


  Conductors that do not obey Ohm's law. As temperature increases, so does resistance
• As temperature increases


  Resistance increases for non-ohmic conductors
• We will only be working with ohmic conductors
• Gradient-resistance


  Gradient = 1