Electricity

• What are the 14 circuit symbols you are expected to know?

  Open Switch, closed switch, cell, battery, diode, resistor, variable resistor, LED, lamp, fuse, voltmeter, ammeter, thermistor, LDR
• Define current with units?

  The rate of flow of charge. measured in amps
• Define voltage with units?

  The energy per unit charge. Measured in volts
• Define resistance with units?

  A measure of how hard it is the current to flow. Measured in ohms.
• What four factors effect resistance? Brief description how they effect resistance?

  length – longer -higher resistance

  Thickness – wider-lower resistance

  temperature-higher temperature-higher resistance

  Material – more free electrons-lower resistance
• What is ohms law?

  Current is directly proportional to potential difference while at constant temperature
• What is a ohmic component

  A ohmic conductor, obeys ohms law, eg a resistor at constant temperature or a wire
• describe how you would sketch the three graphs for a resistor, bulb and diode and describe the shape of each of them?

  for all three graphs, current is down voltage goes across

  For ohmic conductor, it’s a straight line through the origin as they obey ohm’s law

  For the filament bulb it’s a curvy line as the bulb gets hot resistance increases so it’s harder for the current to flow

  For the diode, it’s a straight line across and then like curved at the top because it’s only let current flow in One Direction
• Sketch the graph of resistance against temperature for thermistor?

  Resistance on the side temperature on the bottom and it’s a short curve
• Sketch the graph of resistance against light intensity for a LDR?

  Resistance on the side light intensity on the bottom it will be dark at one end and light at the other end and it will be a longer curve
• Where would you find thermistor in real life?

  Anything that responds to temperature change for example, fridges, freezers and central heating
• where would you find an LDR in real life?

  Anything that responds to changing light intensity for example street lamps, automatic car headlight, ornaments which come on at night
• What is a series circuit?

  A circuit with only one loop/branch only
• what is a parallel circuit?

  A circuit which has two or more loops/branches
• Describe current in a series circuit?

  Current is the same anywhere in series
• Describe potential difference in a series circuit?

  Potential difference is shared between components
• Describe resistance in a series circuit?

  Total resistance in series is the sum of the resistance of each component
• Describe current in a parallel circuit?

  Current is shared between branches in parallel
• Describe resistance in a parallel circuit?

  Total resistance in parallel will always be less than the smallest individual resistor
• What is the mains voltage and frequency?

  Voltage: 230V Frequency: 50Hz
• What is the difference between AC and DC?

  AC is alternating current where current flows in different directions

  DC is direct current where current flows in only One Direction
• Mains appliances use three core cables what are the wires inside?

  Live wire which is brown, neutral wire which is blue and the Earth wire which is green and yellow
• What is the function and voltage of each of the wires?

  Live wire carries alternating potential difference at 230 V

  Neutral wire completes the circuit at 0 V

  The safety wire to stop the appliance becoming live and provides path of least resistance so should have 0 V and it protects a person from getting an electric shock
• What is a fuse and how does it work?

  A fuse is a safety device, which will melt when the current gets too high. This breaks the circuit meaning electricity cannot flow. it comes in ratings of 3 A, 5 A, 10 A and 13 A and that is the maximum current the fuse can withstand