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Electricity (Charge, Current & Potential Difference (Circuit Symbols
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Electricity
Charge, Current & Potential Difference
Circuit Symbols
A resistor at constant temperature (ohmic conductor)
Current is directly proportional to potential difference. Doubling the potential difference doubles the current in the circuit. The resistance remains the same. Plotting a graph of potential difference against current gives a straight line passing through the origin (0,0).
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Conventional current flows around a circuit from the positive (+) side of the cell to the negative (-). However the electrons are flowing around the circuit in the opposite direction from the negative (-) side of the cell to the positive (+).
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Charge (Q) – charge is measured in coulombs (C).
A single electron carries a charge of 1.6 x 10-19 C.
Current (I) – is measured in amperes (A).
Current is the rate of flow of charge. A current of 1 A means that 1 coulomb of charge flows past a point in a circuit every second. ( 1 A = 1 C s-1 ) Current is measured in a circuit using an ammeter which is placed in series with the component of interest in the circuit.
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Potential difference (V) – is measured in volts (V).
Potential difference is the work done per unit charge. A potential difference of 1 V means that 1 joule of work is done per coulomb of charge. ( 1 V = 1 J C-1) Potential difference in a circuit is measured using a voltmeter which is placed in parallel with the component of interest in the circuit.
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Resistance (W) – is the ratio of potential difference across a component to the current flowing through it, it is measure in ohms (W).
Resistance
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Superconductors
Have 0 resistivity, below a critical temperature
Used to reduce energy loss or produce strong magnetic fields
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