Circuits

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Circuit Devices

Diode --> made from semiconductor material such as silicon
-It is used to regulate the potential difference in circuits
-It lets current flowly freely through it it ONE DIRECTION ONLY (there's a very high resistance in the reverse direction)

Light-Emitting Diodes (LED) --> emits light when a current flows through it in the forward direction
-They are being used more and more as lighting because they use a much smaller current than other forms of lighting
-They indicate the presence of current in a circuit
-Often used in appliances such as TVs to show they're switched on
-Used for numbers on digital clocks, traffic lights and remote controls 

Light-Dependent Resistors (LDR) --> dependent on the intensity of light
-Bright light- resistance falls
-Darkness- resistance is highest
-Applications include, automatic nightlights, burglar detectors etc

Thermistors --> temperature dependent resistor
-Hot conditions- resistance drops
-Cool conditions- resistances goes up
-They make useful temperature detectors e.g. electronic thermostats 

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Series Circuits

  • The different components are connected in a line, end to end, between the positive and negative of the power supply (except for the voltmeter- connected in parallel)
  • If you remove or disconnect one component, the circuit is broken and they all stop
  • This is generally not very handy

Potential Difference is Shared:
-the total P.D. of the supply is shared between the components
-they all add up to equal the source voltage e.g. V= V1 + V2 + ...

Current is the Same Everywhere:
-the same current flows through all parts of the circuit e.g. A1 = A2

Resistance Adds Up:
-the total resistance is just the sum of all the resistances e.g. R= R1 + R2 + R3
-the bigger the resistance of a component, the bigger its share of the total P.D. 

Cell Voltages Add Up:
-2 batteries of 1.5 V connected in series, they supply 3V between them

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Parallel Circuits

  • Each component is separately connected to the positive and negative of the supply
  • If you remove or disconnect one of them, it will hardly affect the others
  • Able to switch everything on and off separately e.g. household electrics

P.D. is the Same Across All Components:
-all components get the full source of P.D. e.g. V1 = V2 = V3
-so, idential bulbs connected in parallel will be at the same brightness

Current is Shared Between Branches:
-the total current flowing around the circuit is equal to the total of all the currents through the separate components e.g. A = A1 +A2 + ...
-there are junctions where the current either splits or rejoins 
-the total current going into a junction has to equal the total current leaving
-so, if 2 identical components are connected in parallel, the same current will flow through each component

Voltmeters and Ammeters are Exceptions to the Rule:
-ammeters are always connected in series, even in a parallel circuit
-voltmeters are always connected in parallel with a component, even in a series circuit

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