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In the physical sciences, potential difference is the difference
in potential between two points in a conservative vector field. In engineering, it is
sometimes described as the across variable, where flux is the through variable. The product of
the flux and the potential difference is the power, which is the rate of change of the
conserved quantity, e.g., energy.
- In electrical engineering the potential difference is the voltage, i.e. the difference between the initial and final points
of an electrostatic potential.
- In fluid systems the potential difference is the difference in pressure.
- In thermal systems the potential difference is the difference in temperature
- In mechanics, the potential difference is the difference in gravitational potential between two points.
Electrical potential difference
A potential difference between two points gives rise to a "force" called an electromotive force or
emf that tends to push electrons or other charge-carriers from one
point to the other. Common sources of emf are the battery, the electrical generator and the capacitor. Between two points in an electrical
circuit the potential difference is equal to the difference in their electrical potentials.
It is defined as the amount of work per charge needed to move electric charge from the second point to the first, or equivalently, the
amount of work that unit charge flowing from the first point to the second can perform. In the SI system of units, potential difference, electrical potential and electromotive force are measured in volts, leading to the commonly used term voltage and the symbol
V. Named after Alessandro Volta, one volt is defined to be one joule of energy per coulomb of charge.
If one thinks of an electrical circuit in analogy to water circulating in a network of pipes, driven by pumps in the absence
of gravity, then the potential difference corresponds to the pressure difference between two points. If there is a pressure difference between two points, then water
flowing from the first point to the second will be able to do work, such as driving a turbine.
Instruments for measuring potential differences include the voltmeter, the
potentiometer (measurement device), and the oscilloscope. The voltmeter works by measuring the current through a fixed resistor, which, according to
Ohm's Law, is proportional to the potential difference across it. The
potentiometer works by balancing the unknown voltage against a known voltage in a bridge circuit. The cathode-ray oscilloscope works by amplifying the potential difference and using it to
deflect an electron beam from a straight path, so that the deflection of the beam
is proportional to the potential difference.
Voltage is additive in the following sense: the voltage between A and C is the same as the voltage between
A and B plus the voltage between B and C. Two points in an electric circuit which are
connected by an (ideal) conductor without resistance will have a potential difference of zero. But other pairs of points may also
have a potential difference of zero. If two such points are connected with a conductor, no current will flow through the
connection. The various voltages in a circuit can be computed with Kirchhoff's circuit laws.
A potential difference is generated between the ends of an electrical conductor that moves perpendicular to a magnetic field.
See also
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