chapter 3 electricity, components and circuits. chapter 3 electricity, components & circuits...

Chapter 3

Electricity, Components and Circuits

Chapter 3Electricity, Components & Circuits

Today’s agenda

• Fundamental concepts of electricity & circuits

• Voltage & current

• Resistance, capacitance & inductance

• Reactance, impedance & resonance

• Common types of electronic components

• How basic types of radios are made

04/21/23 21 July 2010-30 June 2014 Technician

Chapter 3Electricity

Electric current (represented by the letter “I”) is the flow of electrons. Current is measured in amperes (A) with an ammeter. Amperes are abbreviated as “amps”.

Current is always measures as the flow through something (e.g., wire, electronic component, etc).

Voltage (represented by the letter “E”) is the electromotive force that makes electrons move and voltage is measured in “volts” (“V” or “v”) with a voltmeter.



The polarity of voltage is either positive or negative.

• Negative voltage repels electrons

• Positive voltage attracts electrons

The Earth’s surface acts as the universal reference for voltage measurements and is called “earth ground”, “ground potential” or simply “ground”.



A circuit is any path through which current can flow.

If two or more devices are connected in a circuit so that the same current must flow through all of them in sequence, that is called a “series” circuit.

SeriesCircuit

#1

#2

#304/21/23 51 July 2010-30 June 2014 Technician


If two or more devices are connected in a circuit so that the same voltage is present across all of them at the same time, that is called a “parallel” circuit.

#1 #2 #3

ParallelCircuit




Voltmeters are connected in parallel with a component or circuit to measure voltage. Whereas, ammeters are connected in series with a component or circuit to measure current.


A “closed circuit” provides an uninterrupted, endless path for the flow of current. This is normally done intentionally by design.

An “open circuit” is made by breaking the path of current in a circuit.

A “short circuit” is a direct connection between two points in a circuit. Although similar to a “closed circuit”, “short circuits” are usually unintentional.



The basic electrical test instruments are simple meters:

• Voltmeters• Ammeters• Ohmmeters

All of these meters are found in the common and relatively inexpensive “multimeter”. They come in analog and digital to measure voltage, current and resistance.



Multimeters can tell you a lot:

If you are measuring the resistance of a circuit and the reading starts out low but gradually increases, that indicates the presence of a large value capacitor.

The flexibility of the multimeter means that it’s important to use it properly. Measuring voltage or connecting the probes to a “live” circuit when the meter is set to measure resistance is a common way to damage a multimeter.04/21/23 101 July 2010-30 June 2014 Technician


All materials impede the flow of electrons to some degree. This property is called “resistance”. Resistance is the opposition of a material to current flow.

Resistance (represented by the letter “R”) is measured in ohms (represented by the Greek letter Omega (Ω)) with an ohmmeter.

If you know any two of current (I), voltage (E) and resistance (R), you can calculate the missing value



Materials in which electrons flow easily in response to an applied voltage are “conductors”.

Materials such as copper and gold are good conductors as is salt water. So is the human body!

Materials that resist or prevent the flow of electrons are “insulators”. Glass, ceramic, plastic, dry wood and paper and other non-metals are examples of “insulators”.



Georg Ohm discovered the proportional relationship between voltage, current and resistance in 1827.

Ohm’s Law states that current is directly proportional to voltage and inversely proportional to resistance.

The more a material resists the flow of electrons, the lower the current will be in response to voltage across the material.


Georg Ohm


E = I x R

I = E / R

R = E / I

If you know any two of I, E or R, you can determine the missing value.

As an equation, we can state that I = E / R, E = I x R and R = E / I.

Current (I) equals voltage (E) divided by resistance (R).

Voltage (E) equals current (I) multiplied by resistance (R).

Resistance (R) equals voltage (E) divided by current (I).04/21/23 141 July 2010-30 June 2014 Technician


E = I x R

I = E / R

R = E / I

What is the resistance of a circuit in which a current of 3 amperes flows through a resistor connected to 90 volts?

Resistance (R) equals voltage (E) divided by current (I).

R = E ÷ I

R = 90V ÷ 3A

R = 30 ohms or 30Ω04/21/23 151 July 2010-30 June 2014 Technician


E = I x R

I = E / R

R = E / I

What is the resistance of a circuit in which the applied voltage is 12 volts and the current flow is 1.5 amperes?


R = E ÷ I

R = 12V ÷ 1.5A



E = I x R

I = E / R

R = E / I

What is the resistance of a circuit that draws 4 amperes from a 12-volt source?


R = E ÷ I

R = 12V ÷ 4A



E = I x R

I = E / R

R = E / I

What is the current of a circuit with an applied voltage of 120 volts and a resistance of 80 ohms?


I = E ÷ R

I (current) = 120V ÷ 80Ω

I = 1.5 amperes or 1.5A04/21/23 181 July 2010-30 June 2014 Technician


E = I x R

I = E / R

R = E / I

What is the current flowing through a 100-ohm resistor connected across 200 volts?


I = E ÷ R


I = 2 amperes or 2A04/21/23 191 July 2010-30 June 2014 Technician


E = I x R

I = E / R

R = E / I

What is the current flowing through a 24-ohm resistor connected across 240 volts?


I = E ÷ R


I = 10 amperes or 10A04/21/23 201 July 2010-30 June 2014 Technician


E = I x R

I = E / R

R = E / I

What is the voltage across a 2-ohm resistor if a current of 0.5 amperes flows through it?


E = I x R

E = 0.5A x 2Ω

E = 1 volt or 1V04/21/23 211 July 2010-30 June 2014 Technician


E = I x R

I = E / R

R = E / I

What is the voltage across a 10-ohm resistor if a current of 1 ampere flows through it?


E = I x R

E = 1A x 10Ω



E = I x R

I = E / R

R = E / I

What is the voltage across a 10-ohm resistor if a current of 2 amperes flow through it?


E = I x R

E = 21A x 10Ω



Power (represented by the letter “P”) is measured in watts which are abbreviated as “W”.

Power is the rate at which electrical energy is used.

Power is measured with a wattmeter.

Power (P) equals voltage (E) multiplied by current (I).

As with Ohm’s Law, if you know any two of P. E or I you can determine the missing quantity.

P = E x I

P = I2 x R

I = P / E

E = P / I

P = E2 / R



How much power is being used in a circuit when the applied voltage is 13.8 volts and the current is 10 amperes?

P = E x I

P = I2 x R

I = P / E

E = P / I

P = E2 / R


P = E x I

E = 13.8V x 10A

E = 138 watts or 138W

X



How much power is being used in a circuit when the applied voltage is 12 volts and the current is 2.5 amperes?

P = E x I

P = I2 x R

I = P / E

E = P / I

P = E2 / R


P = E x I

E = 12V x 2.5A

E = 30 watts or 30W

X


Current (I) equals power (P) divided by voltage (E).

I = P ÷ E

I = 120W ÷ 12V

I = 10 amperes or 10A


How many amperes are flowing in a circuit when the applied voltage is 12 volts and the load is 120 watts?

P = E x I

P = I2 x R

I = P / E

E = P / I

P = E2 / R

?



AC and DC

It’s electricity – not a rock band.

Current that flows in one direction all the time is “direct current” or “dc”.

Current that regularly reverses direction is “alternating current” or “ac”

Direct Current

Alternating Current



Like current, a voltage that has the same polarity (the same direction from positive to negative) is “direct current” or “dc”.

A voltage that regularly reverses polarity is an ac voltage.

Batteries and solar cells are a source of dc voltage and current.

Household power is suppled by an electrical utility in the form of ac voltage and current.



Just like radio waves, a complete sequence of ac current flowing, stopping, reversing and stopping again is a “cycle”.

The number of cycles per second is the ac current’s frequency. The same is true for voltage.

The frequency of household ac voltage is 50 or 60 Hz while radio signals used by radio amateurs have frequencies in the MHz and GHz range.


Chapter 3Components & Units

Electronic circuits are made from components, each of which performs a discrete function: storing or dissipating energy, routing current or amplifying a signal.

The three most basic types of electronic components are “resistors”, “capacitors” and “inductors” (aka “coils”).

The amount of resistance in a resistor is measured in “ohms”(Ω), “kilo-ohms” (kΩ) and “mega-ohms” (MΩ).

Just like a valve in a water pipe restricts the flow of water, a resistor opposes or restricts the flow of electrical current. 04/21/23 311 July 2010-30 June 2014 Technician


The value of a resistor is determined by a color code system.

Resistors come in fixed and variable values.

A variable resistor is called a “potentiometer” or “pot” and is used to adjust voltage as in volume control.



The schematic symbol for a fixed resistor:

Fixed

The schematic symbol for a variable resistor:

Variable




4

7 100

5%

47 x 100 = 4700 ± 5%

or

47 x 100 = 4.7k ± 5%



Capacitors store electrical energy in the electric field created by a voltage between two conducting surfaces (e.g., metal foil) called “electrodes” and separated by an insulating material called a “dialectric”.

Storing energy in this manner is called “capacitance” and is measured in farads (F). Remember: frequency is symbolized by the lower case “f”



Capacitors used in radio circuits have values measured in “picofarads” (pF), “nanofarads” (nF) and “microfarads” (μF).

Capacitors are used to smooth out ac voltage changes.

A capacitor cannot pass dc current.

Michael Faraday



Like all components, capacitors come in many shapes, sizes and values.

Fixed



+

Electrolytic

Electrolytic capacitors (polarized) are used as rectifier and power supply filters



Variable

“Variable” or “Tuning” capacitors vary the frequency of resonant circuits/filters and adjust impedance matching circuits



Inductors store magnetic energy in the magnetic field created by current flowing through a wire. Inductors smooth out current changes.

This is called inductance and it is measured in nano-henrys (nH), micro-henrys (μH), milli-henrys (mH) and henrys (H). Joseph Henry

Inductors are made of wire wound in a coil, sometimes around a core of magnetic material that concentrates the magnetic energy.



Inductors



Schematic symbols for inductors



Transformers are made from two or more inductors that share their stored energy. This allows energy to be transferred from one inductor to another while changing the combination of voltage and current.

A transformer is used to transfer energy from a home’s 120 V ac outlet to a lower voltage for use in electronic equipment.



Transformer schematic symbols



All three types of basic components are available as “adjustable” or “variable” models.

A variable resistor is also called a “potentiometer” or “pot”.

Variable resistors are used to adjust voltage or potential, such as for volume control.

Variable capacitors and inductors are used to tune radio circuits for a variety of purposes.



Variable Resistors

Variable capacitor

Variable inductor



Reactance and Impedance

In a resistor, ac voltages and currents are exactly in step (“in phase”): When voltage increases so does current and vice-versa.

In capacitors and inductors, the relationship between ac voltage and current is changed so that there is an “offset” in time between changes as energy is stored and released.

This means that voltage and current have a phase difference.




In a capacitor, the change in current occurs ahead of voltage changes because of the smoothing action of the capacitor.

In an inductor, changes in the ac current lag behind changes in voltage because the inductor resists changes in current.

Opposition to ac current flow is called “reactance” and is represented by “X” and is measured in ohms – just like a resistance.




Reactance from a capacitor is called “capacitive reactance”.

Reactance from an inductor is called “inductive reactance”.

The combination of resistance and reactance is called “impedance” and is represented by the letter “Z” and is also measured in ohms.

Radio circuits almost always have both resistance and reactance.

Chapter 3Types of Radios & Radio Circuits


Resonance

In a circuit with both capacitive and inductive reactance, at some frequency the two types of reactance will be equal and cancel each other out. As a result, the ac current and voltage are back in step with each other. This condition is called “resonance”.

The frequency at which resonance occurs is call the “resonant frequency”.

Chapter 3Types of Radios & Radio Circuits


Resonance

Circuits that contain both capacitors and inductors will have at least one resonant frequency and are called “resonant circuits” or “tuned circuits”.

Tuned circuits act as “filters” either passing or rejecting signals at the resonant frequency.

chapter 3 electricity, components and circuits. chapter 3 electricity, components & circuits...

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