Electricity, Components and Circuits Class...

12019-4 Technician License Course

Electricity, Components and Circuits

Class 3


Electricity – Current and Voltage

• Radios are powered by electricity and radio signals are a form of electrical energy.

• A basic understanding of how we control electricity allows you to better install and operate your radio.

• Electrical charge can be positive or negative.• Opposite charges attract each other

• Electrical current is the flow of electrons.– Electrons are negatively-charged atomic particles, usually surrounding an atom’s positively-

charged nucleus of protons (positive) and neutrons (neutral – no charge)– Electrons move in response to an electromotive force and can move independently of

atoms

• Current: the movement of electrons, measured in amperes (A) by an ammeter, and represented by I in formulas

• Voltage: the amount of electromotive force (emf), also called electrical potential, measured in volts (V) by a voltmeter, represented by E or V in formulas

• For example most mobile radios require about 12 volts to function

• Resistance: the opposition to the movement of electrons, measured in ohms (Ω) by an ) by an ohmmeter and represented by R in formulas.

• Resistance is like friction and turns electrical energy into heat when current flows.

• Conductors permit current flow (low resistance) and insulators block current flow (high resistance).


Electrical Pressure and Flow

• The flow of water through a pipe is a good analogy to understand the three characteristics of electricity and how they are related.

• Voltage from a source of electrical energy causes current to flow.• Resistance is a material’s opposition to the flow of current.• Voltage, current and resistance affect each other. • For example, higher voltage (bigger push) causes more current (more flow).


Direct and Alternating Current

• Current that flows in only one direction, is called direct current (dc).– Batteries are a common source of dc.

• Current that flows in one direction then in the opposite direction is called alternating current (ac).– Household current is ac

• AC current reverses direction on a regular basis– Each process of reversing is a cycle.– The number of cycles per second is

frequency, measured in hertz (Hz).• 1 Hz = 1 cycle per second


Circuits

• For current to flow, there must be a path from one side of the energy source to the other side of the source – this path is called a circuit.

• There must be a pipe (conductive path) through which the water (current) can flow.

• There are two types of electric circuits.

• Series and parallel


Circuits

Series Circuits

• Series circuits provide one and only one path for current flow.• The voltage divides between the components depending on their type and value.

Parallel Circuits

• Parallel circuits provide multiple paths for current flow.• The current divides between the components depending on their type and value.


Circuits


Economies of Scale - The Multimeter

• The basic electrical test instruments are simple meters Voltmeters Ammeters Ohmmeters.

• Multimeters use a single meter to measure all three basic electrical values of voltage, current and resistance.

• Multimeters VOM (volt-ohm-meter) DVM (digital volt meter)

• Measuring voltage when the multimeter is set to Ohms can damage the multimeter.

• When measuring high voltages, make sure the multimeter and leads are rated to handle that voltage

• You may find unexpected ways to use a multimeter. • For instance, when measuring the resistance in a circuit and

the meter indicates a low value, but the reading gradually increases, look for the presence of a capacitor in the circuit.


Resistance and Ohm’s Law

• All materials oppose the flow of electrical current– Resistance

• Conductors– Metals

Copper Gold Aluminum

• Insulators– Non Metals

Glass Ceramics Paper Plastics


Resistance and Ohm’s Law

• E represents voltage – Units – volts (V)• I represents current – Units – amperes (A)• R represents resistance – Units – ohms (Ω) by an )

R=EI

I=ER

E=I×R


For example, The voltage required to cause 2 amperes of current to flow through 15 ohms is:

E=I×R=2×15=30 Volts

To use the Ohm's law circle we are solving for “E” so cover up the “E” and plug in the other two numbers

Finding Voltage

Finding Current

For example, The current flowing through a resistance of 60 ohms with voltage 120 volts is:

I=ER

=12060

=2 Amperes

To use the Ohm's law circle we are solving for “I” so cover up the “I” and plug in the other two numbers


For example, The resistance in a circuit with a current of 3 amperes flowing through it with a voltage 120 volts is:

To use the Ohm's law circle we are solving for “R” so cover up the “R” and plug in the other two numbers

Finding Resistance

R=EI=

1203

=40 Ohms


Power

• Any time energy is expended, power is consumed.• Electrons moving through resistance expend electrical energy and consume power.• Power is the rate at which energy is consumed.• Power is measured in units of watts (W).


Power

• Power is calculated as the product of voltage and current

• Like Ohm’s Law, if you know two of the values, you can calculate the third.

P=I×E

I=PE

E=PI


When the applied voltage is 10 volts DC and the current is 5 amperes the power being used is:

To use the power law circle we are solving for “P” so cover up the “P” and plug in the other two numbers

Finding Power

P=I×E=5×10=50 Watts

Finding Current

When the applied voltage is 10 volts DC and the load is 140 watts the current is:

I=PE

=14010

=14 Amperes

To use the power law circle we are solving for “I” so cover up the “I” and plug in the other two numbers


When the current is 5 amperes and the load is 50 watts the Voltage is:

Finding Voltage

E=PI=

505

=10 Volts

To use the power law circle we are solving for “E” so cover up the “E” and plug in the other two numbers


Components and Units


Basic Components

• To make an electronic device (like a radio) do something useful (like a receiver), we need to control and manipulate the flow of current.

• There are a number of different electronic components that are used to do this.


The Resistor

• The function of a resistor is to restrict the flow of current.• Remember Ohm’s Law:

I = E / R

E = I X R Resistance is measured in Ohms using the Greek symbol omega (Ω)) Schematic symbol

Arrow indicates adjustable value, such as for a volume control which controls voltage.

Potentiometer or “Pot”


The Capacitor

• The function of a capacitor is to store electrical energy – called capacitance.– Measured in farads– Acts like a battery– Stores energy in an electric field created by voltage between the

electrodes with insulating dielectric material between them


The Inductor• The function of an inductor is to store magnetic energy – called inductance.

– Measured in henrys– A coil of wire around a core of air or magnetic material like iron or ferrite– Stores energy in a magnetic field created by current in the wire

Schematic symbol


The Transformer• A pair of inductors sharing a common core

– Also share their magnetic field– Used to transfer energy from one circuit to another without a direct

connection– Changes the ratio of voltage and current – For example, changes 120V ac to a lower voltage (12V ac)

Schematic symbol

Core


Many electronic components use markings, called a color code, to indicate their value.

A resistor with four colored stripes, red-violet-brown-gold, was made to have a resistance value of 270 Ω) with a tolerance of 5% (256.5 Ω) to 283.5 Ω)).

Other components have their value printed directly on their body, but may encode the value to save space.

A capacitor labeled with `683' has a value of 68 x l03 pF.

Markings and Tolerances


Reactance

• Capacitors and inductors store energy, rather than dissipating it like resistors.• Energy storage creates an effect called reactance (symbol X) that acts like a

resistance in opposing the flow of ac current.• Current and Voltage are out of phase• Capacitors create capacitive reactance (XC )

• Inductors create inductive reactance (XL )

• Measured in Ohms• The effects of each are complementary

Impedance

• The combination of resistance (R) and reactance (X) is called impedance, represented by the symbol Z.

• Measured in Ohms.• Impedance represents a circuit’s opposition to both ac and dc currents.• Impedance is written as a complex number. ie. R±jX 50+j32 or 35-j75


Resonance

• A component’s reactance depends on frequency: • XL increases with frequency while XC decreases.

• At the frequency for which a circuit’s XL and XC are equal, their effects cancel.

• This is the circuit’s resonant frequency.• At resonance, a circuit has only resistance, which affects ac and dc current equally.

Capacitors and inductors connected together create a tuned circuit.• When XL and XC are equal, the circuit is resonant.• If C or L are adjustable the resonant frequency can be varied or tuned.

Resonant or Tuned Circuit


Things to Study for the Next Class• Reading Assignment:

Chapter 3 – From Diodes, Transistors and Integrated Circuits Pages 3-10 through End of Chapter

Study Question Pool Number(s)

T0A04 and T0A05T6A08 and 6A09T6B01 thru T6B11T6C01 thru T6C13T6D01 thru T6D04T6D07T6D09 and T6D10T7A03T7A05T7A08

Electricity, Components and Circuits Class...

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