Circuit Elements

An electrical circuit is an interconnection of electrical circuit elements. These circuit elements can be categorized into two types, namely active circuit elements and passive circuit elements.

Some Definitions/explanations of electrical terms

(unit: coulomb, C; letter symbol: q or Q )
The electric charge is the most basic quantity in electrical engineering, and arises from the atomic particles of which matter is made.
Potential Difference
(unit: volt, V; letter symbol: v or V )
The potential difference, also known as voltage, is the work done (or energy required) to move a unit positive charge from one point to another (across a circuit element). Thus the change in work done $dw$ when a charge $dq$ moves through a potential difference of v
$$dw = v.dq$$
(unit: ampere, A; letter symbol: i or I )
The electric current is the rate of charge flow in a circuit.
$$i = {dq \over dt} \,\quad q = ∫i dt$$
(unit: joule, J; letter symbol: w or W )
The Energy is the capacity to do work. Thus in electrical quantities this may be expressed as
$$∫ dw = ∫ v.dq = ∫ v.i.dt$$
(unit: watt, W; letter symbol: p or P ) The electric power is the rate of change of energy.
$$p = (v)(i) = ({dw \over dq})({dq \over dt})$$
$$p = {dw \over dt}$$

Common usage of letter symbols

It is common practice to use the simple letters (such as $v$, $i$, $p$, $w$) to represent quantities which are varying with time, and capital letters (such as $V$, $I$, $P$, $W$) to represent quantities which are constants. But this need not always be done and is a useful practice rather than a rule. With representation of elements, obviously this practice does not exist as they are not time variables.
The letter $j$ is normally used for the imaginary operator $√-1$ as $i$ is almost invariably used to denote current.

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