# L2a - Elements of Circuits The most common circuit elements...

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Elements of Circuits The most common circuit elements are the: ± Resistor ± Capacitor ± Inductor ± Diode and they represent the building blocks of most electronic circuits. Resistance (R) The electrical resistance of a conductor is defined by: I V R = where I is the current flowing through the conductor when the potential difference (PD) across it is V . The unit of electrical resistance is the ohm ( ), and is defined as being the resistance of a conductor through which a current of one ampere is flowing when a PD across it is one volt, i.e. 1 = 1 V A -1 . In an ohmic device, the current passing through the conductor is directly proportional to the voltage applied across it. The figures below show various current voltage relationships for different devices. V 0 I V I I V Ohmic conductor (like a resistor) Water voltmeter Gas discharge tube

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Resistivity ( ρ ) The electrical resistivity (units is m) of a material is defined by: A L R = where L is the length of the conductor, A is the area of the cross-section, and is the resistivity. The resistivity of silver is about 1.6x10 -8 /m, iron is about 10 -9 /m, and about 10 12 /m for Pyrex. Silver is obviously a great conductor, and Pyrex would be a rather poor choice for anything but an insulator. Therefore, to reduce the resistance of a wire, we should make it
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L2a - Elements of Circuits The most common circuit elements...

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