Basic of electrical and electronics


Electrical voltage is defined as electric potential difference between two points of an electric field.

Using water pipe analogy, we can visualize the voltage as height difference that makes the water flow down.

V = φ2 – φ1

V is the voltage between point 2 and 1 in volts (V).

φ2 is the electric potential at point #2 in volts (V).

φ1 is the electric potential at point #1 in volts (V).

In an electrical circuit, the electrical voltage V in volts (V) is equal to the energy consumption E in joules (J)

divided by the electric charge Q in coulombs (C).


V is the voltage measured in volts (V)

E is the energy measured in joules (J)

Q is the electric charge measured in coulombs (C)

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Volt is the electrical unit of voltage or potential difference (symbol: V).

One Volt is defined as energy consumption of one joule per electric charge of one coulomb.

1V = 1J/C

One volt is equal to current of 1 amp times resistance of 1 ohm:

1V = 1A ⋅ 1Ω



The joule is the standard unit of energy in electronics and general scientific applications. One joule is defined as the amount of energy exerted when a force of one newton is applied over a displacement of one meter. One joule is the equivalent of one watt of power radiated or dissipated for one second.

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Energy is the capacity of a physical system to do work. The common symbol for energy is the uppercase letter E. The standard unit is the joule, symbolized by J. One joule (1 J) is the energy resulting from the equivalent of one newton (1 N) of force acting over one meter (1 m) of displacement. There are two main forms of energy, called potential energy and kinetic energy.

Kinetic energy is observable as motion of an object, particle, or set of particles. Examples include the falling of an object in a gravitational field, the motion of a charged particle in an electric field, and the rapid motion of atoms or molecules when an object is at a temperature above zero Kelvin.

Matter is equivalent to energy in the sense that the two are related by the Einstein equation:

E = mc2

where E is the energy in joules, m is the mass in kilograms, and c is the speed of light, equal to approximately 2.99792 x 108 meters per second.

In electrical circuits, energy is a measure of power expended over time. In this sense, one joule (1 J) is equivalent to one watt (1 W) dissipated or radiated for one second (1 s). A common unit of energy in electric utilities is the kilowatt-hour (kWh), which is the equivalent of one kilowatt (kW) dissipated or expended for one hour (1 h). Because 1 kW = 1000 W and 1 h = 3600 s, 1 kWh = 3.6 x 106 J.

Heat energy is occasionally specified in British thermal units (Btu) by non scientists, where 1 Btu is approximately equal to 1055 J. The heating or cooling capability of a climate-control system may be quoted in Btu, but this is technically a misuse of the term. In this sense, the system manufacturer or vendor is actually referring to Btu per hour (Btu/h), a measure of heating or cooling power.

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