Fundamentals of Electricity Franklin County Amateur Radio Club Technician Class License Course Class...

Fundamentals of ElectricityFundamentals of Electricity

Franklin County Amateur Radio ClubFranklin County Amateur Radio Club

Technician Class License CourseTechnician Class License Course

Class 3 – Fundamentals of ElectricityClass 3 – Fundamentals of Electricity

Bob Solosko W1SRBBob Solosko W1SRB

• All materials are made up of atoms• Atoms are composed of protons, neutrons and electrons

• electrons have a positive charge• protons have a negative charge

• In some materials, electrons are held tightly to the atom

• these materials are insulators• examples:

• wood, ceramics, plastics

• In some materials, electrons are held loosely to the atom are free to move around

• these materials are conductors• examples:

• copper, silver, aluminum

ProtonsAnd

Neutorns

Electrons

Electricity is about how electrons flows through materials

Controlling the flow of electrons is the

foundation for the operation of – Radios

– Ipods

– Computers

– Telephones

– Recorders

– Stereos

– House lights

• There are three characteristics to electricity:– Electromotive Force– Current– Resistance

• All three must be present for electrons to flow

Electromotive Force (EMF or E)– “electro”: electrons– “motive”: movement– “force”: the push

• Electromotive force is the push that causes electrons to move through a conductor

• Measured in volts

• Usually referred to as voltage

Current (I)

• Current is the amount of electrons that flow through a conductor over time

• Measured in amperes – i.e., amps

Resistance (R)

• A material's opposition to the flow of electric current; measured in ohms.

• Measured in ohms

• All materials, even very good conductors have some resistance

• Electrons are confined to conductors, i.e., wires

• Electrons flow only through a closed circuit

– Similar to the flow of water in the pipes of a closed hot water

heating system

– Like a pump that provides the force to push water through

the pipe, a battery provides the electrical push, i.e., voltage,

to push electrons through the wire

• Electrons are confined to conductors, i.e., wires

• Electrons flow only through a closed circuit

Closed circuit, current flows Open circuit, no current flows

switch switch

• Electrical circuits

switch

battery

Resistance(resistor)

voltage

current

Relationship between Voltage (E), Current (I) and Resistance (R)

• It takes a certain force (i.e., voltage) to get a certain amount of current (amps) to flow against a specific reststance (ohms)

• A greater resistance requires a greater force (i.e., higher voltage) to get the same amount of current to flow

Ohm’s Law

Voltage = Current x Resistance

E = I x RVolts = amps x ohms

Ohm’s Law

Current = Voltage/ResistanceI = E / R

Resistance = Voltage/CurrentR = E / I

Ohm’s Law - Summary

• E is voltage– Units - volts

• I is current– Units - amperes

• R is resistance– Units - ohms

• R = E/I• I = E/R• E = I x R

battery

Resistancevoltage

current

10 V5 Ω

• Electrical circuits – Ohms law

E = I x RI = E / RR = E / I

If voltage V = 10 volts (10 V) and resistance R = 5 ohm (1 Ω)

Then current I = E / R = 10 / 5 = 2 amps (2 A)

E = I x RI = E / RR = E / I

If voltage = 10 V and current = 20 A

Then resistance R = E / I = 10 / 20 = ½ Ω

battery

Resistancevoltage

current

10 V1/2 Ω

E = I x RI = E / RR = E / I

If voltage = 10 V and current = 20 A

Then resistance R = E / I = 10 / 20 = ½ Ω

If resistance = 100 Ω and current = 3 A

Then voltage V = I x R = 3 x 100 = 300 V

battery

Resistancevoltage

current

300 V100 Ω

battery

Resistancevoltage

current

300 V100 Ω

battery

Resistancevoltage

current

300 V100 Ω

3 A300 V 300 V

The voltage across the resistor is the same as the voltage across the battery

battery

Resistancevoltage

current

300 V100 Ω

battery

Resistancevoltage

current

300 V100 Ω

The current is the same anywhere in the circuit

• Moving electrons do work and expend energy:

– generate heat

– generate light

– run motors

– generate and receive radio signals

– compute

• Power is the rate at which electrical energy is generated or consumer

– measured in the units of Watts

• Power = voltage x current P = E x I

Power• Power = voltage x current

P = E x II = P/EE = P/I

• Example 1: 60 watt light bulb– E = 120v, P = 60w, I = ?, R = ?

120 V I

60w bulb

Power• Power = voltage x current

P = E x II = P/EE = P/I

• Example 1: 60 watt light bulb– E = 120v, P = 60w, I = ?, R = ?

I = P/E = 60/120 = ½ AR = E/I = 120/½ = 240Ω

120 V I

battery

Resistancevoltage

current

300 V100 Ω

60w bulb

• Example 2: – E = 300v, R = 100Ω, I = ?, P = ?

I = E/R = 300/100 = 3AP = E x I = 300/3 = 300w

Types of Current

• When current flows in only one direction, it is called direct current (DC).– batteries are a common source of DC.– most electronic devices are powered by DC.

• When current flows alternatively in one direction then in the opposite direction, it is called alternating current (AC).– your household current is AC.– radio waves are AC

Electrical Circuits

• Series circuit – one and only one path for current flow

• Parallel circuit– alternative paths for current flow

battery

Resistor orother component

current

battery

current

Components: the resistor

• restricts (limits) the flow of current through it

• unit of resistance: ohm (Ω)

• (also dissipates energy as heat)– incadescent lightbulbs– electric stoves

• Circuit Symbol

• A resistor for which the resistance can be changed is a variable resistor or potentiometer

• Circuit Symbol

variableresistor

potentiometer

• A resistor for which the resistance can be changed is a variable resistor or potentiometer

• Circuit Symbol

Components: the battery

• source of DC voltage

• stores energy

• provides energy to a circuit

• Circuit Symbol

• temporarily stores electrons and electric current– stores energy in an

electrostatic field

• Unit of capacitance: farad

• composed of parallel metal plates with a non-conductive material (dielectric) in between– dielectric can be air, plastic,

glass, etc.

• A capacitor for which the capacitance can be changed is a variable capacitor

Components: the capacitor• Circuit Symbol

• Unit of capacitance: farad– a coulomb is a unit of electrical charge– 1 coulomb = 6,250,000,000,000,000,000 electrons– 1 farad is 1 coulomb/volt

Components: the capacitor

switch

Note: once the capacitor is charged, no more current flows, and the capacitor acts like an open circuit (an open switch)

switch

~AC voltage

switch

~AC voltage

Note: a capacitor allows AC current to flow

• Capacitive reactance (XC)

– the opposition to alternating current due to capacitance

– unit of capacitive reactance: ohms

– is inversely proportional to the signal frequency and the

capacitance

– XC = - 1 / (2fC)

• Note: if f = 0, i.e. DC current, XC = ∞, i.e., an open circuit

• stores electric current– stores energy in a magnetic

field– any wire with a current

flowing through it creates a magnetic field

• unit of inductance: henry

• magnetic field is strengthened by coiling wire, i.e., inductance is increases

• an inductor for which the inductance can be changed is a variable inductance

• An inductor may have an iron core to increase the inductance

• Circuit Symbol

Components: the inductor

• Inductive reactance (XL)

– the opposition to alternating current due to inductance

– unit of inductance reactance: ohms

– is proportional to the signal frequency and the inductance

– XL = + 2fL

• Note: if f = 0, i.e. DC current, XL = 0, i.e., an short circuit

Components: the inductor

• Impedance is the total opposition to alternating current due to

reistance, capacitance and inductance

– unit of impedance: ohms

– Z = √ R2 + (XC + XL)2

• Resonance:

When XC = XL,

Then Z = R

Impedance (Z):

~AC voltage

• controls the flow of current– like an electronically controlled

valve.

– like the faucet in your sink

• used to amplify a signal or as an on-off switch

– A small current or voltage on the “base (B)” lead causes a large change in the current flowing between the “emitter (E)” and “collector (C)” leads

• Circuit Symbol

Components: the transistor

valve.

• Circuit Symbol

valve.

• Circuit Symbol

valve.

• Circuit Symbol

• a collection of components contained in one device – replaces many individual

components

– a “black-box” for a specific function

– examples:• amplifier• switch• voltage regulator• mixer• display controller

Components: the integrated circuit

• Circuit Symbol

• Allows current to flow in only one direction

• Circuit SymbolComponents: diode

• interrupts the flow of current if the current exceeds some value

– Fuses blow – one time protection.

– Circuit breakers trip – can be reset and reused.

• Circuit Symbol

Components: fuses and circuit breakers

• Special type of diode that emits light when current passes through it

Components: light emiting diode (LED)

Other Circuit Symbols:

Circuit Diagrams: examples

Amplifier

Light control Antenna tuner

Power supply – converts 120VAC to DC

• resistor values may be ohms (Ω), kilo ohms (kΩ) or mega ohms (MΩ)

• capacitor values typically are microfarads (μf) or pico farads (pf)

• inductance values are typically milli henrys (mh) or micro henrys (μh)

• frequencies are typically kilo hertz (kHz) or mega Hertz (MHz)

• voltage is often volts (V) milli volts (mV) or micro volts (μV)

• current is often amps (A), milli amps (mA) or micro amps (μA)

Very Large and Very Small Numeric Values: Units

• decibels are used to compare values that vary over a very large range

– signal levels, amplifier gain, sound levels

• decibles compare values on a logrithmic scale

• 3 dB is a factor of 2

– a 3 dB gain in an amplifier means that the output level is twice the input level

• 10 dB is a factor of 10

– a 10 dB gain in an amplifier means that the output level is 10 times the input level

• decibels add:

– 3 dB = 2 times

– 6 dB = 2 x 2 = 4 times

– 9 dB = 2 x 2 x 2 = 8 times

– 12 dB = 2 x 2 x 2 x 2 = 16 times

– 10 dB = 10 times

– 20 dB = 10 x 10 = 100 times

– 30 dB = 10 x 10 x 10 = 1000 times

Very Large and Very Small Numeric Values: decibels (dB)

Fundamentals of Electricity Franklin County Amateur Radio Club Technician Class License Course Class...

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