topic 2

• what is a circuit?

  A circuit is a closed loop that electrons flow through
• what is potential difference?

  Potential difference is the force driving the flow of electrons in a circuit.
• what is current?

  Current is a measure of the flow of electrons around a circuit
• what charge does the long and short line on the cell symbol symbolise?

  longer line is positive, shorter line is negative
• what do circuits with fixed resistors look like on an I-V graph and why?

  In circuits that contain fixed resistors, when potential difference increases, current increases proportionally (as long as the resistance is constant), so it's I-V graph is a straight line
• what do filament lamps look like on an I-V graph and why?

  Filament lamps’ resistance increases as current increases, meaning current increases slower and slower, making a “s” shape on the I-V graph
• what do diodes look like on an I-V graph and why?

  Diodes’ I-V graphs only show up at the positive side because it controls the direction of current flow, making it flow only one way
• what equation links voltage currant and resistance?

  V (voltage) = I (current) x R (resistance)
• what is conventional current?

  When current moves from the positive terminal to the negative terminal
• what is resistance?

  a measurement of how much the flow of electrons in a circuit is being opposed/resisted
• what is charge?

  a measure of the total current that flows within a certain period of time
• what is the equation that links charge current and time?

  Q (charge) = I (current) x t (time)
• what do cells and batteries do?

  provide electric power
• what do switches do?

  control the flow of electricity
• what do fuses do?

  they break if the temperature is too high so that the circuit stops
• what do diodes do?

  only allow current to move in one direction
• what do LEDs do?

  emit light when current flows in a forward direction
• what do ammeters and voltmeters measure and which type of circuit are they connected to?

  ammeters measure current, and are connected in series

  voltmeters measure voltage and are connected in parallel
• what are variable resistors?

  they allow us to modify resistance
• what do LDRs do?

  they have high resistance in darkness and low resistance in bright light
• what do thermistors do?

  they have low resistance in higher temperatures and high resistance in low temperatures
• what are series circuits?

  In a series circuit, there is only a single loop, and the components are connected one after the other.
• what happens when a single component is broken in series?

  If any component is broken, the whole circuit will be broken
• describe voltage in series circuits

  The total voltage is shared between components
• describe resistance in series circuits

  The total resistance is the sum of the individual resistances between components.
• describe current in series circuits

  The total current is constant, so an ammeter can be placed anywhere
• what happens to the voltage as resistance increases in components

  the components will have a greater share of voltage
• what are parallel circuits?

  Parallel circuits have more than one loop, and each loop generally has a single component
• what happens when a single component breaks in parallel?

  If a single component breaks, the circuit can still function
• describe potential difference in parallel

  The potential difference is equal throughout
• describe current in parallel

  The current is shared between components
• what happens to resistance as more components are added in parallel?

  The more components you add in parallel, the less resistance there is. This is because there is more paths that current can flow through, so it can flow more easily, therefore resistance decreases
• what are the energy and power formulas?

  • Energy (J) = Power (W) x time (s) (E=Pt)
  • Energy (J) = Voltage (V) x Current (A) x time (s) (E = VIt)
  • Energy (J) = Charge flow ( C) x Voltage (V) (E = QV)
  • Power (W) = Current (A) x Voltage (V) (P = IV)
  • Power (W) = (Current (A))² x Resistance (Ω) (P = I²R)
• how do power stations work?

  Power stations work by generating a high amount of heat, using the steam to turn turbines, and converting the kinetic energy to electrical energy.
• what are the two transformers and what do they do?

  Step up transformers increase the voltage to about 440,000 volts, wires transfer this current to populated areas, and a step down transformer decreases the voltage to 230V to keep it at a safe level for domestic use.
• why is the current very low and the voltage very high in transformers?

  Whenever a high current flows, lots of energy is lost as thermal energy. Therefore the current is kept very low, and the voltage is heavily increased instead, so the electricity is transferred quicker as well
• what is AC current?

  AC (alternating current) means the current/voltage is constantly fluctuating from positive to negative - changing directions (50 times per second - 50Hz). AC is the most widely used type of current
• what is DC?

  DC (direct current) is when the current is only flowing in one direction. This is usually found in cells and batteries
• what do oscilloscopes do?

  Oscilloscopes display the pd-time graphs
• what 3 cables do plugs contain?

  Plugs contain 3 cables: the live wire, neutral wire and earth wire