Physics - Voltage
The term voltage refers to the amount of energy given to a coulomb of
charge as it passes through a battery or supply, or the amount of energy
that a coulomb of charge gives up as it passes through a load. The term
voltage refers to an energy _change, _also called a potential difference;
actual energy values are not important. For example, a nine volt battery
gives each passing coulomb nine more joules of energy regardless of the
energy that the coulomb of charge may already possess. A light globe that
is causing a voltage drop of 20 volts may actually mean that a coulomb of
charge with 240 joules of energy passes through the globe and exits with
only 220 joules of energy.
When measuring a voltage value, the voltmeter is essentially comparing
energy values either side of a circuit component, hence a voltmeter is
placed 'in parallel' in a circuit.
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