As a river flows through its course
so does current flow through a wire.
The picture on the right illustrates
this situation.
D.C. Basics
I. Ohm's Law
As a river flows through its course
so does current flow through a wire.
The picture on the right illustrates
this 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
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 to symbolspage.
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
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 the Table 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.
