Electric Voltage

in #busy6 years ago

simple-circuit.jpg


Electric Voltage


Voltage, potential difference, is the energy required to move a unit charge through an element, measured in volts (V).


Basic Concept


To move the electron in a conductor in a particular direction requires some work or energy transfer. This work is performed by an external electromotive force (emf). This emf is also known as voltage or potential difference.


voltage.gif

The voltage between two points a and b in an electric circuit is the energy (or work) needed to move a unit charge from a to b; mathematically,

vab = dw/dq

where, w is energy in joules (J) and

q is charge in coulombs (C).


Unit of Electric voltage


Voltage is measured in volts(V) in honor of the Italian physicist Alessandro Antonio Volta (1745–1827), who invented the first voltaic battery.

A voltage, potential difference, of 1 volt (V) exists between two points if 1 joule (J) of energy is exchanged in moving 1 coulomb (C) of charge between the two points.

1 volt = 1 joule/coulomb = 1 newton-meter/coulomb


Type of Electric Voltage


Voltage can be :

  • DC voltage
  • AC voltage

dc - voltage.PNG

A dc voltage is a voltage that remains constant with time. A dc voltage is commonly produced by a battery.


ac - voltage.PNG

A sinusoidally time-varying voltage is called an ac voltage. ac voltage is produced by an electric generator.


Polarity of Electric Voltage


voltage_polarity_1.PNG

Figure shows the voltage across an element connected to points a and b. The plus and minus signs are used to define reference direction or voltage polarity. The vab can be interpreted in two ways:

  1. Point a is at a potential of vab volts higher than point b.
  2. The potential at point a with respect to point b is vab. It follows logically that in general

vab = -vba


voltage_polarity_2.PNG

In Fig, we have two representations of the same voltage. In Fig(a), point a is +9V above point b; in Fig(b), point b is -9V above point a. We may say that in Fig(a), there is a 9-V voltage drop from a to b or equivalently a 9-V voltage rise from b to a. In other words, a voltage drop from a to b is equivalent to a voltage b rise from b to a.


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