Voltage, electric potential difference, electric pressure or electric
tension (formally denoted ∆V or ∆U, but more often simply as V or
U, for instance in the context of Ohm's or Kirchhoff's circuit laws)
is the difference in electric potential between two points. The
voltage between two points is equal to the work done per unit of
charge against a static electric field to move a test charge between
two points. This is measured in units of volts (a joule per coulomb);
moving 1 coulomb of charge across 1 volt of electric potential
requires 1 joule of work.
Contents 1 Definition 2 Volt 3 Hydraulic analogy 4 Applications 4.1 Addition of voltages 5 Measuring instruments
6 Typical voltages
7
Definition[edit] Given two points in space, x A displaystyle x_ A and x B displaystyle x_ B , voltage is the difference in electric potential between those two points. From the definition of electric potential it follows that: Δ V B A = V ( x B ) − V ( x A ) = − ∫ r 0 x B E → ⋅ d l → − ( − ∫ r 0 x A E → ⋅ d l → ) displaystyle Delta V_ BA =V(x_ B )-V(x_ A )=-int _ r_ 0 ^ x_ B vec E cdot d vec l -left(-int _ r_ 0 ^ x_ A vec E cdot d vec l right) = ∫ x B r 0 E → ⋅ d l → + ∫ r 0 x A E → ⋅ d l → = ∫ x B x A E → ⋅ d l → displaystyle =int _ x_ B ^ r_ 0 vec E cdot d vec l +int _ r_ 0 ^ x_ A vec E cdot d vec l =int _ x_ B ^ x_ A vec E cdot d vec l The electric field around the rod exerts a force on the charged pith ball, in an electroscope In a static field, the work is independent of the path
Working on high voltage power lines Specifying a voltage measurement requires explicit or implicit specification of the points across which the voltage is measured. When using a voltmeter to measure potential difference, one electrical lead of the voltmeter must be connected to the first point, one to the second point. A common use of the term "voltage" is in describing the voltage dropped across an electrical device (such as a resistor). The voltage drop across the device can be understood as the difference between measurements at each terminal of the device with respect to a common reference point (or ground). The voltage drop is the difference between the two readings. Two points in an electric circuit that are connected by an ideal conductor without resistance and not within a changing magnetic field have a voltage of zero. Any two points with the same potential may be connected by a conductor and no current will flow between them. Addition of voltages[edit] The voltage between A and C is the sum of the voltage between A and B and the voltage between B and C. The various voltages in a circuit can be computed using Kirchhoff's circuit laws. When talking about alternating current (AC) there is a difference between instantaneous voltage and average voltage. Instantaneous voltages can be added for direct current (DC) and AC, but average voltages can be meaningfully added only when they apply to signals that all have the same frequency and phase. Measuring instruments[edit]
Instruments for measuring voltages include the voltmeter, the
potentiometer, and the oscilloscope. The voltmeter works by measuring
the current through a fixed resistor, which, according to Ohm's Law,
is proportional to the voltage across the resistor. The potentiometer
works by balancing the unknown voltage against a known voltage in a
bridge circuit. The cathode-ray oscilloscope works by amplifying the
voltage and using it to deflect an electron beam from a straight path,
so that the deflection of the beam is proportional to the voltage.
Typical voltages[edit]
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References[edit] ^ Demetrius T. Paris and F. Kenneth Hurd, Basic Electromagnetic
Theory, McGraw-Hill, New York 1969, ISBN 0-07-048470-8, pp. 512,
546
^ P. Hammond,
External links[edit] Look up voltage in Wiktionary, the free dictionary. Electrical voltage V, current I, resistivity R, impedance Z, wattage P Elementary explanation of voltage at NDT Resource Center Authority control |