circuit

• Metals


  Have free electrons that are able to move from atom to atom
• Voltage


  Pushes free electrons around the circuit
• Electrons


  Negative, move towards the positive terminal in the circuit
• Conventional current


  Current flows from the positive terminal to the negative one
• Series circuit


  • Only one route for the current to take, components cannot be turned off separately
• Parallel circuit


  • Junctions so current may take different routes, each component can be turned off separately
• Measuring current


  Using an ammeter, placed in series to measure the current that passes through them
• Current is conserved, the current leaving and entering the power source are always the same</b>
• Current will split at a junction, but the sum of currents entering a junction always equals the sum of currents leaving the junction
• Potential difference (p.d.)


  Measure of how much energy is transferred to each coulomb of charge flowing around a circuit
• Measuring potential difference


  Using a voltmeter, placed in parallel to measure the potential difference across a component or circuit
• In a parallel circuit, the p.d. is the same across each branch
• In a series branch of a circuit, the p.d. across each component is equal to the total voltage
• Electric charge


  Measured in coulombs (C), 1 coulomb of charge has flowed through a circuit when there has been a current of 1 amp flowing for 1 second
• Electrons


  Carry a tiny charge of 1.6 x 10^-19 C
• Electrical resistance


  Measured in ohms (Ω), a wire has one ohm of resistance when a current of one amp is produced by a potential difference of one volt
• Resistors in a series circuit

  • Total resistance is the sum of the separate resistances, potential difference is divided between the components
• Resistors in a parallel circuit

  • Total resistance decreases, each branch experiences the same potential difference
• Variable resistor


  A resistor that can be controlled, increasing resistance decreases current, decreasing resistance increases current
• Increasing potential difference across components

  Causes different changes in the current that flows, can be shown on graphs
• Light dependent resistor (LDR)


  Has lower resistance when placed in bright light
• Thermistor


  Has lower resistance when placed in warmer temperatures
• Investigating resistance


  Set up circuit, vary voltage, measure current and voltage, use V=IR to calculate resistance
• Energy is transferred by heating when current passes through a circuit, the greater the resistance the more energy is transferred and the hotter the circuit becomes
• Heating can be useful in appliances like kettles and heaters, but not useful in plugs, wires and computers as it dissipates energy away from the circuit
• Heating can cause burns and increase the risk of fires
• Reducing resistance


  • Use thicker wires, use metals with lower resistance, cool the circuit
• Power


  Measured in watts (W), the rate at which energy is transferred
• Mains electricity


  Delivered from power stations to homes through the national grid, arrives at 230 V and 50 Hz
• Direct current (d.c.)


  Charges flow in one direction, provided by cells, batteries and solar panels
• Alternating current (a.c.)


  Charges flow in changing directions, produced by rotating generators
• Safety features


  • Switches, fuses, earth wire, circuit breakers
• Fuse


  Contains a thin wire that melts if too much current passes through, breaking the circuit
• Earth wire


  Connects metal parts to the ground so current flows through the wire and not the user
• Circuit breaker


  Detects a difference in current between the live and neutral wires and 'trips' to break the circuit
• in a parallel circuit, there are two or more paths that current can flow through
• the total resistance of a series circuit is equal to the sum of all resistances
• The total resistance of a parallel circuit is less than any individual resistance
• In a series circuit, the potential difference across each component is the same as the p.d. across the whole circuit.
• A fuse is used to protect electrical appliances by melting when too much current flows through it