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D.C. Basics

I. Ohm's Law

As a river flows through its courseso does current flow through a wire.The picture on the right illustratesthis situation.

OHM'S LAW: Hence from this simple explanation we arrive to the major law of all electronics:

Ohm's law which states that the potential drop through a section of a wire is proportional to the

current flowing through the wire and the resistance across the piece of wire or : V = I * R

which can also be written as: I = V/R and R = V/I .

II. Basic Electric Circuit

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Resistor R = 10 Ohms Symbol: R

Voltage V = 10 Volts

I : Current ; S1 : Switch Symbol:

Note that in the circuit diagram the symbols are missing, for a list of symbols go tosymbolspage.Since a quick referral may be needed for upcoming circuits.

As shown in the Basic Electric Circuit, the current I flows from the positive side of the battery or

power supply V as long as the switch S1 is closed. There is a ground symbol for reference to the

voltages and currents in the circuit. This will prove as a necessary reference, as seen later.

The units for the voltage are volts (10 V in this case --meaning 10 volts) and the units for resistance

are Ohms (10 in this case meaning 10 Ohms). From Ohm's Law: I =V/R =10/10 = 1 Amp, since

the units for current are amps. We need to use units to "quantify" the measurements we have for our

electric parameters, in this case: voltage, resistance and current.

III. Basic Components.Resistor Types

simple resistor surface-mount resistor

potentiometer (variable resistor) and symbol

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Two main components were already introduced. These are: The battery or power supply and the

resistor. Both are shown in pictures above. The battery can be a chemical battery which stores an amount

of potential energy or a power supply as shown in the D.C. Electronics home page. The resistor can also

come in different forms as shown above, with the axial lead component which has the color bands as the

most general form. Two other basic components which will be introduced later on are the Capacitor and

the Inductor. In any case, the use of components and electrical parameters will give us the need to use

Units and Prefixes. These are catalogued in theTable of Units.

To measure resistor values directly from their color bands take the first two colors and multiply to the power

of "ten raised to the value of the third color". The values for the colors are: black=0, brown=1, red=2,

orange=3, yellow=4, green=5, blue=6, violet=7, gray=8, white=9. The gold or silver bands as the

fourth band indicate a 5 or 10 percent tolerance respectively.

D.C. Electronics

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