Pearson Science Double Award Physics 2: Electricity
Pearson Science Double Award notes on charge, circuits, resistance, power and electrical safety.
Electric circuits transfer energy while charge is conserved. This note follows the 4SD0 Double Award boundary: mains safety, circuit behaviour and electrical quantities are included, while electrostatics, electric fields, oscilloscope treatment and the separate-Physics additions at points 2.22 to 2.28 are excluded.
Current, charge and voltage
Current is the rate of flow of charge:
In a solid metal, negatively charged electrons carry current. Conventional current is defined in the direction positive charge would move, so it is opposite to electron drift. Charge does not get used up in a component. At a junction, total current entering equals total current leaving because charge is conserved.
Voltage is energy transferred per unit charge. One volt is one joule per coulomb, and
A cell transfers chemical-store energy to charges. Components then transfer electrical energy to thermal, light, kinetic or sound pathways. Voltage is measured across a component with a voltmeter in parallel; current is measured through it with an ammeter in series.
Resistance and component behaviour
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