Download - Fundamentals of Electricity Franklin County Amateur Radio Club Technician Class License Course Class 3 – Fundamentals of Electricity Bob Solosko W1SRB.

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

2 A

• 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

20 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

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

3 A



battery

Resistancevoltage

current

300 V100 Ω

3 A



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

3 A



battery

Resistancevoltage

current

300 V100 Ω

3 A

3 A

3 A

The current is the same anywhere in the circuit


Power

• 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




switch

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




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

B

E

C


• 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


• 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)