THE BASIC ELECTRONIC CONCEPTS
Electronics deals with the design, analysis and applications of electronic circuits. This page introduces you to the circuit and explains the operation of its basic components. First of all, what is
circuit? Technically speaking, it is a collection of parts connected by conductors that forms a closed path through which electric current can flow to achieve a particular functionality.
Now, what is current? By definition, the
electric current is an orderly flow of electric charges. It is measured as the rate of charge flow past a given area:
I=Q/t, where I  current in amps, Q charge in coulomb, t  time in seconds. Charge in turn is a fundamental property of the matter carried by some elementary particles, such as electrons and protons. This property determines these particles electromagnetic interaction. It is measured in coulombs (C), and it exhibits two states, positive and negative. In classical physics the charge of any system, body, or particle is an integer multiple of the elementary charge
e, which is equal to 1.602×10
^{−19} coulombs. By convention, the proton has a charge of
+e, and the electron has
e.
Although electric current in conductors is produced primarily by the motion of electrons, it has long been the convention to take the direction of electric current as if it were the positive charges which are moving. In other words, in circuit analysis we consider the current flow from plus to minus.
The flow of the charges is influenced by electric fields. When a charged particle moves in the field from a point A to a point B, specific work is done on this particle by electrical forces. As a result of this work the particle's potential energy changes. The value of this work per unit charge is called
voltage:
V=W/Q.
Voltage is measured in volts (1 V is 1 joule per coulomb). Since power by definition is work per unit time, the amount of power transfer (i.e., rate at which electric energy is transformed by the flow of current) is then given by the equation
P=W/t
=V×Q/t=V×I.
FUNDAMENTAL ELECTRICAL COMPONENTS
Basic parts used in electronics are classified into passive (such as resistors, capacitors and inductors) or active (such as transistors and diodes). When we do practical circuit design and analysis, we normally replace real parts by socalled lumped circuit abstractions. These abstractions are idealized elements that reflect certain key aspects of real device operation and allow us to view a circuit as a set of discrete or "lumped" elements.
The three basic electrical components are resistor, capacitor and inductor. An ideal
resistor is defined as an element for which the ratio of voltage divided by current is constant. This constant ratio is called resistance: R=V/I. A resistor is a dissipative element: it does not store energy, but simply removes it from the circuit by converting to heat.
ELECTRICAL UNITS SUMMARY

QUANTITY 
SYMBOL 
NAME OF
THE UNIT 
RELATIONSHIPS WITH
OTHER QUANTITIES 
Capacitance 
C 
farad (F) 
Q/V 
Charge 
Q 
coulomb (C) 
I×t 
Conductance 
G 
siemens (S) 
I/V or 1/R 
Current 
I 
ampere (A) 
Q/t 
Inductance 
L 
Henry (H) 
V×Δt/ΔI 
Voltage 
V 
volt (V) 
I×R 
Resistance 
R 
ohm (Ω) 
V/I 
Note: t time (in seconds) 
Capacitor is a device consisting of two conductors separated by a dielectric. When a DC voltage is applied to a capacitor, certain charges with equal value and opposite signs will appear on these conductors so that the potential difference produced by these charges will be equal to the applied voltage. The capacitance C is defined as the ratio of the charge magnitude on each conductor to the voltage:
C = Q/V, where C is in farads (F). An ideal capacitor does not pass a direct current, while allowing only AC to pass:
i(t)=C×ΔV(t)/Δt.
Inductor is an twoterminal element resisting any change of electric current through it. An ideal inductor has zero resistance and in a steady state mode has zero DC voltage across its terminals. When AC current passes through an inductor, the AC voltage that appears across its terminals is due to its own magnetic field and Faraday's law of electromagnetic induction:
V(t)=L×Δi(t)/Δt.
Below you find additional information on electronics, circuit design and analysis as well as learning and career resources.