Topic 10

• Current flow consisting of charges that continually change direction. These oscillations usually occur at a set frequency.

  Alternating Current
• A device connected in series with a component to measure the current that flows through it.

  Ammeter
• The unit of current.

  Amperes (Amps)
• A safety device that cuts of the power supply if a surge of current passes through it. They can be reset and are quicker than fuses.

  Circuit Breaker
• The unit of charge.

  Coulomb
• The sum of the currents entering a junction must always equal the sum of the current leaving it. This is a consequence of the conservation of charge.

  Currents at a Junction
• A component that only allows current to flow through in the forward direction. They have very large resistance in the reverse direction.

  Diode
• Current flow consisting of charges flowing in a single direction only. Batteries and cells provide it.

  Direct Current
• The green and yellow striped safety wire connected to metal casings, that prevents and appliance from becoming live.

  Earth Wire
• The rate of flow of electrical charge. Its value is the same at any position in a singe closed loop. In metals, the charges that flow are electrons.

  Electric Current
• Electrical energy is transferred to thermal energy when current does work against a resistance. In metals this is a result of collisions between electrons and ions.

  Energy Transfer in Circuits
• A light emitting component consisting of an enclosed metal filament. Its resistance increases as the filament’s temperature increases.

  Filament Lamp
• A safety device consisting of a thin metal filaments that melts and cuts off the power supply if there is a surge in current, they are connected to the live wire.

  Fuse
• A device that gives out light when a current flows through it. Current can only flow through it in one direction, and a minium voltage must be applied across before it illuminates.

  Light Emitting Diode
• The brown coloured wire that carries the alternating current from the supply in a mains power supply.

  Live Wire
• An a.c. supply, which in the in the UK has a frequency of 50Hz and a voltage of 230V.

  Mains Electricity
• The blue coloured wire that completes the circuit in a mains power supply.

  Neutral Wire
• A conductor whose current flow is directly proportional to the potential difference across it, when held at a constant temperature.

  Ohmic Conductor
• The unit of resistance.

  Ohms
• The current flowing through an Ohmic conductor at constant temperature is directly proportional to the potential difference across it.

  Ohm‘s Law
• Components connected like this have the same potential difference across each component. The total current is equal to the sum of the current flowing through each component.

  Parallel
• The energy that is transferred per unit charge between two points in a circuit. It is often also called a voltage.

  Potential Difference
• The rate at which an appliance transfers energy. For a circuit component it is equal to the product of the current passing through it and the potential difference across it.

  Power
• A measure of the oppositon to current flow.

  Resistance
• The total resistance is less than the lowest individual resistance.

  Resistors in Parallel
• The total resistance is equal to the sum of the resistance of the individual resistors.

  Resistors in Series
• Components connected like this have the same current passing through each component but shared the total potential difference of the power supply.

  Series
• A temperature dependent component, whose resistance increases as its temperature decreases.

  Thermistor
• A device that is connected in parallel with a component to measure the potential difference across it.

  Voltmeter
• The unit of power.

  Watt
• A light sensitive component whose resistance decreases as light intensity increases.


  Light Dependent Resistor (LDR)