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• Potential refers to the the possibility of doing work.
• The symbol for potential difference is E (for electromotive
• The practical unit of potential difference is the volt (V)
• 1 volt is a measure of the amount of work required to move
1C of charge
• When a charge is forced to move because of a potential
difference (voltage) current is produced.
• In conductors - free electrons can be forced to move with
relative ease, since they require little work to be moved.
• So current is charge in motion.
• The more electrons in motion the greater the current.
• Current indicates the intensity of the electricity in
motion. The symbol for current is I (for intensity) and is
measured in amperes.
• The definition of current is: I = Q/T
• Where I is current in amperes, Q is charge in coulombs,
and T is time in seconds.
• In applications requiring the use of current, electrical
components are arranged in the form of a circuit.
• A circuit is defined as a path for current flow.
Open circuit :
current can only exist when
there is conduvtive path. In
the circuit I= 0, since there is
no conductor between points
a and b. we reffered to this as
an open circuit.
Direction of Electron Flow
• The direction of electron flow in our circuit is from the
negative side of the battery, through the load
resistance, back to the positive side of the battery.
Direction of conventional
• The direction of conventional current in our circuit is
from the positive side of the battery, through the load
resistance, back to the negativeside of the battery.
• Circuits that are powered by battery sources are termed
direct current circuits.
• It is the flow of charges in just one direction
• An alternating voltage source periodically alternates or
reverses in polarity.
• The resulting current, therefore, periodically reverses in
• Opposition to the flow of current is termed
• The fact that a wire can become hot from the flow
of current is evidence of resistance.
• Conductors have very little resistance.
• Insulators have large amounts of resistance.
Aresistor impedes the flow of electricity through a circuit.
Resistors have a set value.
Since voltage, current and resistance are related through Ohm’s
law, resistors are a good way to control voltage and current in
2nd band =
3rd band =
4th band =
# of zeros / multiplier
Knowing your unitsis important!
Kilo and Mega are common in resistors
Milli, micro, nano and pico can be used in other
M (mega) = 1,000,000
M (milli) = 1/1,000
u (micro) =1/1,000,000
n (nano) = 1/1,000,000,000 (one trillionth)
p (pico) = 1/ 1,000,000,000,000 (one quadrillionth)
• The amount of current in a circuit is dependent on its
resistance and the applied voltage. Specifically I = V/R
• If you know any two of the factors V, I, and R you can
calculate the third.
• Current I = V/R
• Voltage V = IR
• Resistance R = V/I
• The unit of electrical power is the watt.
• Power is how much work is done over time.
• One watt of power is equal to the work done in one
second by one volt moving one coulomb of charge.
Since one coulomb a second is an ampere:
• Power in watts = volts x amperes
• P = V x I
• P = I² x R
• P = V² / R
Acapacitor stores electricalenergy.
Capacitance is measured in Farads. The small capacitors usually used in
electronics are often measured in microfarads and nanofarads.
Some capacitors are polarized. Note the
different length terminals on one of the capacitors.
Polarity of capacitors
The shorter terminal goes
on the negative side
A diode is a one way valve (or gate) for electricity. It is a
component with an asymmetrical transfer characteristic. A
diode has low (ideally zero) resistance in one direction, and
high (ideally infinite) resistance in the other direction.
Diodes will protect your electronics.
Diode circuit protection
In an electronic circuit, if the polarity is wrong, you can fry
Diodes have abar
on the cathode
Light emitting diode(LED)
A light emitting diode (LED) is a semiconductor light source.
When electricity is passing through the diode, it emits light.
Variable resistor / Potentiometer
Apotentiometer is avariable resistor. As you manually
turn a dial, the resistance changes.
A transistor is a semiconductor device used to
amplify and switch electronic signals and electrical
This is our electronic
How atransistor works
Avoltage or current applied to one pair of the
transistor’s terminals changes the current through
another pairof terminals.
Atransistor is composed of semiconductor material
with at least three terminals
for connection to an external
Transistors have 3pins.
For these transistors:
Bipolar junction transistor.
Collector, Emitter, Base
Useful as motordrivers.Field-effect transistor.
Source, Drain, Gate
MOSFET: Metal-oxide-semiconductor FET
NPN (N-channel FET) versus PNP (P-channel FET)
NPN versus PNP is how the semiconductors are layered.
NPN: Not pointing in
PNP: Pointing in permanently
P-channel FET N-channel FET
An integrated circuit (IC) is a set of transistors that is
the controller or ‘brain’of an electronic circuit.
An input is received, an output is sent out.
Modern microprocessor ICs can have billions of
transistors per square inch!
Printed Circuit Board
Components are attached to a printed
The ‘front’side of the board will have
printed component information, such
as resistor # and resistance, diode type
Holes go all the way through the board
from one side to the other. Through-
hole soldering is needed to connect
components to the board.
Backof Circuit Board
The ‘back’side of the board will have lines indicating
connections between components. The lines on the
back are similar to wires.
Thicker lines denote more current (electrons) moving
Components connect the lines.
• College Physics by Resnick, Halliday and Krane (6th and
• Behzad Razavi, ‘’Fundamental of Microelectronics’’