Circuits

Circuit devices
1. Current only flows in one direction through a diode
  1. Is a device made from a semiconductor such as silicon
  2. It is used to regulate the potential difference of a circuit
2. Light emitting diodes are very useful
  1. They emit light when a current flows through it in the forward direction
  2. Indicate the presence of a current
    1. Used in appliances to show they are switched on
3. Light Dependent Resistor or LDR
  1. Its dependent on the intensity of the light
    1. In bright light the resistance falls
    2. In darkness the resistance is the highest
    3. Used for burglar detectors
4. The resistance of a Thermistor as temperature increases
  1. A temperature dependent resistor
    1. In hot conditions the resistance drops
    2. In cool conditions the resistance goes up
    3. Used for temperature detectors e.g. thermostat
Series Circuit
1. In a series circuit the different components are connected in a line if you remove or disconnect one component the circuit is broken and they all stop
2. Potential difference is shared
  1. In series circuits the total P.D. of the supply is shared between the various components. So the voltage always adds up to equal the source voltage
    1. V = V1 + V2 ...
3. Current is the same everywhere
  1. The same current flows through all parts of the circuit
    1. A1 = A2
  2. The size of the current is determined by the total P.D. of the cells and the total resistance of the circuit
    1. I = V / R
4. Resistance adds up
  1. The total resistance is the sum of all the resistances
    1. R = R1 + R2 + R3..
5. Cell voltage adds up
  1. There is a bigger potential difference when more cells are in series provided the cells are all connected
Parallel Circuit
1. Each component is separately connected to the supply. If you remove or disconnect one of them it will hardly affect the others. Used more
2. P.D is the same across all components
  1. This means identical bulbs connected in parallel will all be at the same brightness
3. Current is shared between branches
  1. In parallel circuits the total current flowing around the circuit is equal to the total of all the currents through the separate components
  2. There are junctions where the circuit either splits or rejoins. The total current going into a junction has to equal the total leaving
4. Voltmeters and Ammeters are exceptions
  1. Ammeters are always connected in series
  2. Voltmeters are always connected in parallel with a component

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Circuits

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