Circuits

Circuits

1. Circuit devices

   • Current only flows in one direction through a diode
     • Is a device made from a semiconductor such as silicon
     • It is used to regulate the potential difference of a circuit
   • Light emitting diodes are very useful
     • They emit light when a current flows through it in the forward direction
     • Indicate the presence of a current
       • Used in appliances to show they are switched on
   • Light Dependent Resistor or LDR
     • Its dependent on the intensity of the light
       • In bright light the resistance falls
       • In darkness the resistance is the highest
       • Used for burglar detectors
   • The resistance of a Thermistor as temperature increases
     • A temperature dependent resistor
       • In hot conditions the resistance drops
       • In cool conditions the resistance goes up
       • Used for temperature detectors e.g. thermostat

2. Series Circuit

   • 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
   • Potential difference is shared
     • 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
       • V = V1 + V2 ...
   • Current is the same everywhere
     • The same current flows through all parts of the circuit
       • A1 = A2
     • The size of the current is determined by the total P.D. of the cells and the total resistance of the circuit
       • I = V / R
   • Resistance adds up
     • The total resistance is the sum of all the resistances
       • R = R1 + R2 + R3..
   • Cell voltage adds up
     • There is a bigger potential difference when more cells are in series provided the cells are all connected

3. Parallel Circuit

   • Each component is separately connected to the supply. If you remove or disconnect one of them it will hardly affect the others. Used more
   • P.D is the same across all components
     • This means identical bulbs connected in parallel will all be at the same brightness
   • Current is shared between branches
     • In parallel circuits the total current flowing around the circuit is equal to the total of all the currents through the separate components
     • There are junctions where the circuit either splits or rejoins. The total current going into a junction has to equal the total leaving
   • Voltmeters and Ammeters are exceptions
     • Ammeters are always connected in series
     • Voltmeters are always connected in parallel with a component

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