**Current and Voltage in Electronics**

In electrical circuits, it is important to keep track of two quantities: voltage and current. Both voltage and current usually change with time.

**What is Voltage
(symbol: V, or sometimes E) **

The cost in energy (work done) necessary to shift a
unit of positive charge from a more negative position (lower potential) to a
more positive location is the voltage between two places (higher potential). It
is, in other words, the energy released as a unit charge goes
"downhill" from a higher to a lower potential. The potential
difference or electromotive force (EMF) is also referred to
as voltage (EMF). The volt is the standard unit of measurement, with
voltages given in volts (V), kilovolts (1kV = 10^{3}V), millivolts (1mV
= 10^{-3}V), and microvolts (1µV = 10^{-6 }V). To transport a
coulomb of charge over a potential difference of one volt, a joule of effort is
required. (A coulomb is a unit of electric charge that roughly matches the
charge of 6 x 10^{18} electrons). The uncommonly used other
voltage levels are nanovolts (1nV = 10^{-9 }V) and megavolts (1MV
= 10^{6} V).

**What is Current
(symbol: I ) **

Current is the rate of flow of electric charge past
a point. The unit of measure is the ampere, or amp, with currents usually
expressed in amperes (A), milliamperes (1mA = 10^{-3}A), microamperes
(1µA = 10^{-6}A), nano-amperes (1nA = 10^{-9}A), or
occasionally picoamperes (1pA = 10^{-12}A). A current of one ampere
equals a flow of one coulomb of charge per second. By convention, current in a
circuit is considered to flow from a more positive point to a more negative
point, even though the actual electron flow is in the opposite direction.

The rate of flow of electric charge through a
location is known as current. Currents are commonly represented in amperes (A),

milliamperes
(1mA = 10^{-3}A),

microamperes (1µA= 10^{-6}A)

nano-amperes
(1nA = 10^{-9}A), or

picoamperes (1pA = 10^{-12}A) as the unit of
measurement.

A current of one ampere corresponds to a charge flow
of one coulomb per second. Even though the real electron movement is in the
opposite drection, the current in a circuit is assumed to flow from a more
positive point to a more negative point.

** Note:**
Usually voltage in a circuit is referred to as voltage between two
points or voltage across two points. Always use the term "current" to
describe the flow of electricity through a device or circuit connection.

It's incorrect, or worse, to state anything like
"the voltage across a resistor..." We do, however, commonly refer to
the voltage at a circuit's point. This is always taken to indicate the voltage
between that point and "ground," which appears to be a well-known
position in the circuit.

Voltages are
formed by working with charges in devices like batteries (electrochemical),
generators (magnetic forces), solar cells (photovoltaic conversion of photon
energy), and so on. We get currents by connecting elements (active and
passive) with voltages.

The oscilloscope is the most valuable electronic
tool because it allows one to look at voltages (and sometimes currents) in a
circuit as a function of time. it is often termed as the "eye" of an
electronic engineer.

Wires, metallic conductors, and the identical
voltage on each of them are used to link items in actual circuits (concerning
ground). But this isn't technically true in the domain of high frequencies or
low impedances. Since wires may be rearranged, an actual circuit does not
have to appear exactly like its schematic representation.

**Rules
about Voltage and Current: **

1. In a circuit, the sum of the currents entering a
point equals the sum of the currents out (conservation of charge). Kirchhoff's
present law is a term used to describe this. A node is a term used by engineers
to describe such a place. As a result, this may deduce the following:
The current in a series circuit (a group of two-terminal devices linked
end-to-end) remains constant.

2. When two components are connected in parallel,
the voltage across them is the same. In other words, the sum of the
"voltage drops" from A to B by one path via a circuit equals the sum
of the "voltage drops" via any other route between A and B. This is
sometimes described as follows: The sum of any closed circuit's voltage is
always zero. This is termed referred to as
Kirchhoff's Voltage Law.

3. A circuit device's power consumption (work per
unit time) is P = VI.

This is simply (work/charge) x (charge/ time). For V
in volts and I in amps, P comes out in watts. Watts are joules per second (IW =
IJ/s).

Usually, power is converted to heat, but it can also
be converted to mechanical work (motors), radiated energy (lamps,
transmitters), or stored energy (batteries, capacitors). Managing the heat load
of a complex system (for example, a computer, where several kilowatts of
electrical energy are converted to heat with the energetically inconsequential
by-product of a few pages of computing output) can be a critical aspect of the
process.

We'll have to expand the basic equation P = VI to
deal with average power when dealing with regularly variable voltages and
currents, but it's correct as a description of instantaneous power as is. Don't
call current "amperage," by the way; that's bush-league. When we get
to resistance, the word "ohmage" will be treated with the same
discretion.

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