Vol 2: Electrical and Electronic Fundamentals Flashcards
Describe matter.
Any substance that has weight and takes up space.
What cannot be broken down into a simpler substance using ordinary chemical means?
Elements.
Define molecule.
The smallest part of a substance that has all the characteristics of that substance.
What are the elements that form molecules?
Atoms.
What type of charge does a proton carry? An electron?
Positive; negative.
When do we consider an atom to be electrically balanced?
When the negative charge of the electron is equal to the positive charge of the proton.
Provide a description of electrical current.
The uniform movement of electrons in a specific direction through a conductor (wire).
What is the term for an atom with eight electrons in the valence shell?
Stable or balanced atom.
What is an atom that has gained an electron called?
Negative ion.
What type of charge does a normal atom that has lost one electron have?
Positive.
The uniform movement of free electrons in a specific direction.
Current flow.
6.28 × 1018 electrical charges.
Coulomb.
One coulomb passing a given point per second.
Ampere.
Symbol for current used in equations.
I
Symbol for quantity of amperes.
A or a.
List four effects of current flow.
Heat, chemical change, magnetism, and physical shock.
Unit of measure for “electrical pressure.”
Volt.
The force which causes electrons to move from atom to atom.
Voltage or emf.
“E.”
Voltage.
Changes mechanical energy into electrical energy.
Generator.
Changes heat energy into electrical energy.
Thermocouple.
Unit of measure for all electrical opposition.
Ohm.
When 1 volt of pressure pushes 1 ampere of current flow through an electrical path, then 1 ohm
of resistance is present.
Ohm’s Law.
“R.”
Resistance.
Name four factors that affect resistance.
Any four of these: length, size, material, temperature, and reactance.
“W” or “P.”
Power
The rate of doing work.
Power
Unit in which electrical motors are rated.
Horsepower
Unit in which generators and regulators are rated.
Watts
Number of watts per horsepower.
746 Watts
What is magnetic material?
A material, usually iron, that has the ability to retain magnetic lines of force.
Define residual magnetism.
The induced magnetism that remains in a magnetic substance after we remove the magnetic field.
What materials do you use to make high-grade artificial magnets?
Aluminum, nickel, iron, and cobalt.
In what direction do the lines of force travel outside a bar magnet?
From the north pole to the south pole.
What action takes place when you place the south pole of one magnet near the south pole of
another?
They repel each other.
State the fundamental laws of magnetism.
Like poles repel each other; unlike poles attract.
When do magnetic lines of force cross?
Never.
What surrounds all current-carrying conductors?
Magnetic lines of force.
How can you strengthen the magnetic lines of force around a conductor?
By forming a number of loops close together.
What three items are necessary to have an electromagnet?
Coil of wire, core material, and current flow.
What type of core is preferred in the construction of relays and solenoids?
Soft iron core.
What is the relationship of the current to the voltage and resistance in a DC circuit according to
Ohm’s law?
The current in amperes is equal to the emf in volts divided by resistance in ohms.
Voltage = 90, current = 30, R = ?
3
Voltage = ?; current = 2; and resistance: R1 = 7, R2 = 5.
24
Voltage = 24; current = ?; resistance: R1 = 10, R2 = 8, R3 = 6.
1
What are the characteristics of resistance, current, and voltage in a DC-series circuit?
(1) The total resistance is the sum of the individual resistors.
(2) The same current flows in each part of the circuit.
(3) The applied voltage divides among the resistors according to their resistance.
What is the rule that pertains to the total current in a parallel circuit?
In a parallel circuit, the total current equals the sum of the current in the branches.
In solving for a value in a series-parallel circuit, what do you do to the circuit first?
Reduce a series-parallel circuit to an equivalent, simplified circuit. Replace each group of parallel resistors
with its equivalent single resistance; then, treat the entire circuit as a series circuit.
In your own words, define Kirchhoff’s voltage law.
The algebraic sum of the voltages around a closed loop must equal zero.
The ability to do work measured in joules.
Energy.
The production of motion against a resisting force measured in joules.
Work.
The rate of doing work measured in watts.
Power.
That which produces a change in motion of a body measured in dynes.
Force.
What formula do you use to compute power in a DC circuit when you only know resistance and
current?
P = I2R.
In a parallel circuit having four equal lamps, with an applied voltage of 120 volts and a total
current flow of 4 amperes, what is the power consumed at each lamp?
120 watts.
How do electrons travel in a circuit?
From negative to positive.
What is the difference in current flow between an AC circuit that contains only resistance and a
DC circuit that contains only resistance?
The current flow in a circuit containing resistance only is the same, regardless of whether the applied
voltage is AC or DC.
Explain Kirchhoff’s law for current as it applies to AC circuits.
AC circuits normally contain inductive and capacitive loads as well. Although they have different formulas
for determining their ohmic values, you can find their voltage and current values the same way as you did
by applying Kirchhoff’s laws for voltage and current in DC circuits.
In an AC circuit, when is the apparent power equal to the true power?
When the circuit consists of pure resistance.
When is the true power less than the apparent power?
When the current and voltage are out of phase due to reactance in the circuit.
What is the formula for power factor?
Power factor =100 watts (true power) / volts amps (apparent power)
A 240-volt AC motor records 35 in-line amperes. The in-line wattmeter shows only 7,600 watts
being consumed. What is the power factor of the AC circuit?
pf = 90.47, or 90.5 percent.
Name the portion of the applied power that produces the magnetic field in an AC circuit.
Wattless power or reactive power expressed in VARs.
What is the function of a generator?
To convert mechanical energy into electrical energy.
What are the types of alternators?
Single-phase and three-phase
In what two ways does an alternator operate?
By the principle of either moving conductors across a magnetic field or moving a magnetic field across the
conductors.
What are the operations of a single-phase alternator?
The first half revolution of the rotor produces a voltage in one direction and completes the first half of the
cycle; the second half revolution produces a voltage in the opposite direction and completes the last half of
the cycle.
What supplies the DC voltage in a three-phase alternator?
An exciter.