Chapter 1Electrical Quantities and Basic Circuits

Section 1-1 Electrical Theory

Section 1-2 Circuits

Section 1-3 Magnetism

Section 1-4 Power

ObjectivesSection 1-1 Electrical Theory

• State the three fundamental parts of an atom and identify their states of charge.

• Define and describe conductors, insulators, and semiconductors.• State the operating function of a diode in a circuit.• State the two forms of energy and give examples of each.• Define voltage and state its unit of measure and common abbreviation.• Define current and state its unit of measure and common abbreviation.• Define resistance and state its unit of measure and common abbreviation.• Determine an unknown voltage, current, and resistance with Ohm’s law.

In an atom, electrons orbit the nucleus in shells that can hold a specific number of electrons.

A conductor allows free electrons to pass readily through it.

Electrons in a conductor atom are held to the atom with minimal force.

Electrons in an insulator atom are held to the atom with a relatively strong force and cannot be moved very easily.

Nonmetallic-sheathed cable is manufactured in various wire sizes and with a specified number of conductors. Printed circuit boards have conductors laminated on an insulated material that makes up the board.

Semiconductors are made from materials that have four valence electrons.

Current flows from negative potential to positive potential and is assisted by free electrons when voltage is applied to N-type material.

When voltage is applied to P-type material, the holes are filled with free electrons that move from the negative potential to the positive potential through the crystal.

In a diode, P-type and N-type materials exchange carriers at the junction of the two materials, creating a thin depletion region.

In forward bias, electrons flow from cathode to anode, but in reverse bias, electrons do not flow.

Manufacturers use a variety of methods to indicate the cathode end of a diode.

The forms of energy used to produce electricity include coal, nuclear power, natural gas, and oil.

Electrical energy is used to produce motion, light, heat, sound, and visual outputs.

Voltage is produced by electromagnetism, heat, light, chemical reaction, pressure, and friction.

DC voltage is produced from batteries, photovoltaic cells, and rectified AC voltage supplies and can vary from almost pure DC voltage to half-wave DC voltage.

AC voltage has one positive alternation and one negative alternation per cycle and is either single-phase (1ϕ) or three-phase (3ϕ).

The amount of current a cell or battery can supply depends on the cell or battery size.

The smaller the AWG number, the greater the cross-sectional area and the heavier the wire.

Abbreviations are used to simplify the expression of common electrical terms and quantities.

Ohm’s law is the relationship between voltage (E), current (I), and resistance (R) in a circuit.

1-1 Checkpoint 1. What are the three fundamental particles contained in atoms?

2. Which particle has a negative charge?

3. What unit is used to measure resistance?

4. What device allows current to flow in only one direction?

5. What type of fuel is used to produce the most amount of electricity?

6. What electrical devices consume the largest share of produced electricity?

7. Voltage is measured in volts (V), but what letter is used to represent voltage?

8. What device converts AC voltage to DC voltage?

9. What are the two types of AC voltage?

10. Current is measured in amperes (A), but what letter is used to represent current?

11. What are the two types of current?

12. Resistance is measured in ohms (Ω), but what letter is used to represent resistance?

13. If resistance is increased in a circuit, does current increase or decrease?

14. If 12 V is applied to a circuit that has a resistance of 500 Ω, how many milliamperes (mA) will flow through the circuit?

15. If 230 V and 6.25 A are measured in a heating element, how much resistance (in Ω) does the heating element have?

ObjectivesSection 1-2 Circuits

• Calculate resistance at any point in a series or parallel circuit.

• Calculate voltages at any point in a series or parallel circuit.

• Calculate current at any point in a series or parallel circuit.

A series connection has two or more components connected so there is only one path for current flow.

A parallel connection has two or more components connected so there is more than one path for current flow.

A series/parallel connection is a combination of series- and parallel-connected components.

Principles of series and parallel circuits can be used to produce several different heat outputs in heating element circuits.

Photovoltaic cells are placed in series to increase the voltage output from a set of photovoltaic cells.

Photovoltaic cells are placed in parallel to increase the current output from a set of photovoltaic cells.

1-2 Checkpoint1. What is the total voltage of six 1.5 V batteries connected in series?

2. If 200 mA total is measured at the 60 V power supply that includes three 100 Ω resistors connected in series, how much current is flowing through each resistor?

3. What is the total voltage of six 1.5 V/10 mA-rated batteries connected in parallel?

4. In a circuit that contains a 100 Ω, a 200 Ω, and a 300 Ω resistor connected in parallel, which resistor would have the largest amount of current flowing through it?

5. If six 3 V/200 mA-rated photovoltaic cells that are connected in series and six more 3 V/200 mA-rated photovoltaic cells also connected in series and then placed in parallel with the first set of six, what is the total voltage of the combination of photovoltaic cells?

6. If six 3 V/200 mA-rated photovoltaic cells that are connected in series and six more 3 V/200 mA-rated photovoltaic cells also connected in series and then placed in parallel with the first set of six, what is the total available current of the combination of photovoltaic cells?

ObjectivesSection 1-3 Magnetism

• Define the molecular theory of magnetism and electromagnetism.

• Define inductance and state how it affects an AC circuit.

• Define capacitance and state how it affects an AC circuit.

The molecular theory of magnetism states that all substances are made up of a number of molecular magnets that can be arranged in either an organized or disorganized manner.

In 1819, the Danish physicist Hans C. Oersted discovered that a magnetic field is created around an electrical conductor when electric current flows through the conductor.

The lines of force (lines of induction) are present along the full length of a conductor.

The total number of lines of force (maxwells) in a one sq cm section of a magnetic field equals the flux density of the field (gauss).

If a conductor is formed into a coil, the lines of force combine, forming a stronger field than the lines of force from a single loop.

The strength of a magnetic field produced by a conductor may be increased by increasing the voltage, increasing the number of coils, or inserting an iron core through the coil.

A conductor formed into a coil produces a strong magnetic field around the coil when current flows through the coil.

Phase shift occurs when voltage and current in an AC circuit do not reach their maximum amplitude and zero level simultaneously.

Capacitors are available in different shapes and sizes.

With a charged capacitor, the electron orbits become stretched toward the positively charged plate.

Current leads voltage in AC capacitive circuits.

An elastic diaphragm and water can be used to represent the internal action of a capacitor.

The current flowing in an inductive AC circuit is directly proportional to the applied voltage and inversely proportional to the inductive reactance.

Capacitive reactance is inversely proportional to the capacitance and the frequency.

1-3 Checkpoint1. Does increasing the number of loops in a coil increase or

decrease the electromagnetic field when current passes through the coil?

2. Inductance is measured in henrys (H), but what letter is used to represent inductance?

3. Capacitance is measured in farads (F), but what letter is used to represent capacitance?

4. Inductive reactance and capacitive reactance oppose a flow of current in a circuit and are stated or measured in what electrical unit?

5. In an AC circuit that includes a coil (inductance), is the voltage and current in phase or out of phase?

ObjectivesSection 1-4 Power

• Define true power and state its unit of measure and common abbreviation.

• Determine an unknown power, voltage, and current with the power formula.

• Calculate power at any point in a series or parallel circuit.• Define reactive power and state its unit of measure and common

abbreviation.• Define apparent power and state its unit of measure and common

abbreviation.• Define power factor and explain its relationship to efficiency.

The power formula is the relationship between power (P), voltage (E), and current (I) in an electrical circuit.

True power is always less than apparent power in a circuit with a phase shift between voltage and current.

A running capacitor can be added to a motor to achieve a power factor of 1.0 and 100% efficiency.

Ohm’s law can be used on circuits with impedance by substituting Z (impedance) for R (resistance) in the formula.

1-4 Checkpoint1. If 8 A are measured in a 120 V circuit, how much power (in W) is

the circuit using?

2. If two 25 W and four 60 W lamps are connected into a parallel circuit, what is the total power (in W) used by the circuit?

3. If a string of sixty 2 W holiday lights are connected in series, what is the total power (in W) of all the lights?

4. What electrical unit is reactive power measured in?

5. What electrical unit is apparent power measured in?

6. What is the ratio between true power and apparent power called?