# Electrical Lessons

Topics: Resistor, Electric current, Volt Pages: 10 (943 words) Published: October 12, 2012
Basic Electronics
Chapter 2
Basic Electrical Principles and
the Functions of Components
Figures in this course book are
reproduced with the permission of
the American Radio Relay League.
This booklet was compiled by
John P. Cross AB5OX

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Basic Electrical Principles
• Conductors - keep loose grip on their electrons and allow electrons to move freely. Metals are usually good
conductors.
• Insulators - keep close hold of their electrons and do not allow free movement of electrons. Glass, wood, plastic,
mica, fiberglass and air are good insulators.
• Electromotive Force (EMF) is the force that moves
electrons through conductors. Its unit of measure is the
Volt. Think of it as pressure.
• Voltage Source - has two terminals (+ and -). Some
examples are car batteries (12 volts DC), D cell batteries
(1.5 volts DC) and a wall socket (120 volts AC).
• Current - is the flow of electrons. It is measured in
amperes.
• Resistance (ohms, Ω) is the ability to oppose an electrical current.
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Circuit Definitions

A circuit must close to be complete!

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Ohm’s Law
• Ohm’s Law relates Current (I), Voltage (E) and Resistance (R)
• The relationship can be written three ways:
»E=IxR
»I=E/R
» R = E/I

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Resistors

Mnemonic: “Black Bears Run On Young
Grass By Violets Growing Wild”
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Resistor Types - Precision

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Resistors - Film Type

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Resistors - Variable

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Calculating Resistance

• Parallel:

• Series:
R=R1+R2+R3+R4
(the voltage adds up)

1/R=1/R1+1/R2+1/R3
(the current adds up)

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Capacitors
• Capacitors store energy in an electric field
• Basic unit of capacitance is the farad (f)
• Series:

1/C=1/C1+1/C2+1/C3

• Parallel:

C=C1+C2+C3

• Capacitance is determined by 3 factors:
» plate surface area
» plate spacing
» insulating material (dielectric)

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Variables Determining
Capacitance

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Parallel Capacitors Increase Plate
Area; increase charge so C

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Capacitors Store Energy in
Electric Field

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Variable Capacitors

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Inductors
• Inductors store energy in a magnetic field
(like a little electromagnet)

• Basic unit of inductance is the henry (h)
• Parallel:

1/L=1/L1+1/L2+1/L3

• Series:

L=L1+L2+L3

• Inductance is determined by 4 factors:
» number of turns
» permeability of the core
» cross sectional area of the core
» spacing of the turns

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Variables Determining
Inductance

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Inductors Store Energy in
Magnetic Field
Current flow-->

Electron flow-->

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Note: current
flows from + to -,
but is carried by
electrons which
flow from - to +

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Types of Inductors

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Power
• Power is the rate of energy consumption.
• The basic unit of power is the watt (W)
• Power can be calculated as follows:
»P = I x E
• Since E = I x R, you can also say:
» P = I2 x R
• Since I = E / R, you can also say:
» P = E2 / R
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Meters - Measuring Current
Ammeter
must be
part of the
circuit to
measure
the current

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VOM multimeter
that
measures
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E, I, R

Meters - Measuring Voltage
Voltmeter
measures
across the
circuit (in
parallel to
the voltage
to be
measured)
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