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# 4.2 - 4.2 Circuits Elements The most common circuit...

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45 4.2 Circuits Elements 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 ( Ω ), 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 Ω = 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. Ohmic conductor (like a resistor) Water voltmeter Gas discharge tube V 0 I V I V

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46 Resistivity ( ρ ) The electrical resistivity (units is Ω m) of a material is defined by: A L R ρ = 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 Ω /m, iron is about 10 -9 Ω /m, and about 10 12 Ω /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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4.2 - 4.2 Circuits Elements The most common circuit...

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