Symbols used in circuit diagrams (3b7)
In order to show the design of a particular circuit on paper, we draw Circuit Diagrams. Everyone uses the same symbols, so that we can all read and understand the diagram. The symbols you need to know for the Foundation Licence are shown below
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Explanation |
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A cell is a small battery. It normally has a potential difference of about 1.5 Volts. Notice that it has two terminals, one has a + (positive), and the other a – (negative). |
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A Battery is several cells connected together to get a higher total potential difference (or voltage). The connections are made internally so from the outside a cell and a battery can look the same.
A Battery provides voltage, but current will only flow if there is a circuit (route) for the electrons to flow out of the battery, through the various wires and components such as resistors and lamps back to the battery. |
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A switch is used to safely start and stop the flow of current in a circuit. Think of a light switch at home |
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A resistor constricts the rate of current flow. The higher the value of the resistor, the less the current will flow. |
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A fuse will allow only a certain amount of current to flow before it breaks and stops the current flowing. It is used as a safety device.
If a circuit is designed to use under 3 Amps, then by putting a 3Amp fuse in the circuit, if a fault develops and the circuit uses a lot more than 3-Amps, then the fuse will break and stop all current flowing in the circuit. |
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The use of an electrical earth is an important safety feature for many items of main-powered equipment |
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A crystal is device that is used to keep an electrical circuit that is oscillating on a steady frequency. It is used a lot to keep radio circuits on one particular frequency. |
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A Lamp gives out light when electrical current flows through it. Think of a light bulb. |
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An antenna (or aerial) is where a radio signal going through the air is picked up. It converts the radio signal into a current in the feeder to the receiver.
It is also used in reverse when transmitting, where it converts the signal in the wire into a signal that goes through the air. |
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A loudspeaker converts electrical signals in wires into sounds we can hear. Televisions, Radios and hi-fi all have loudspeakers in them. |
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A microphone converts sounds into electrical signals in wires. It is the opposite of a loudspeaker. |
