Download File

Review 1
1.
List the three basic elements of an atom and state
the charge of each (positive, negative, or neutral).
Element
Charge
2.
An electron forced out of orbit by an external force is
called a ____________ ____________ .
3.
Conductors allow ____________ free electrons to flow
when an external electric force is applied.
4.
Which of the following materials are good
conductors?
a. copper
b. plastic
c. silver
d. rubber
5.
e.
f.
g.
h.
aluminum
glass
iron
mica
Semiconductor devices can be manufactured to
allow____________ electrons to flow in one direction
and ____________ electrons to flow in the opposite
direction
177
Review 2
1.
Elements are identified by the number of
____________ in orbit around the nucleus.
2.
A material that has an excess of electrons is said to
have a ____________ charge.
3.
A material that has a deficiency of electrons is said
to have a ____________ charge.
4.
Like charges ____________ and unlike charges
____________ .
5.
The force that is applied to a conductor to cause
current flow is ____________ .
6.
Electrons move from ____________ .
a. positive to negative
b. negative to positive
7.
With an increase of length or a decrease of crosssection of a conductor, resistance will ____________ .
a. increase
b. decrease
178
Review 3
1. The basic Ohm’s Law formula is ____________ .
2. When solving circuit problems;
current must always be expressed in ____________ ,
voltage must always be expressed in ____________ ,
and resistance must always be expressed in ____________ .
3. The total current of a simple circuit with a voltage
supply of 12 volts and a resistance of 24 W is ____________ amps.
4. What is the total resistance of a series circuit with
following values: R1=10 W, R2=15 W, and R3=20 W?
____________ W.
5. What is total current of a series circuit that has a 120
volt supply and 60 W resistance?
6. In the following circuit, the voltage dropped across
R1 is ____________ volts and R2 is ____________ volts.
1.5 Ω
1.5 Ω
R1
R2
+
_
12 Volts
7. In the following circuit, voltage dropped across R1 is
____________ volts and across R2 is ____________.
5Ω
2Ω
R1
R2
+
_
100 Volts
179
Review 4
1. The total resistance of a parallel circuit that has four
20 W resistors is ____________ Ω.
2. Rt for the following circuit is ____________ Ω.
R2
R2
R3
10 Ω
20 Ω
30 Ω
3. Rt for the following circuit is ____________ Ω.
R1
R2
5Ω
10 Ω
4. Voltage available at R2 in the following circuit is
____________ volts.
12 Volts
R1
R2
5Ω
10 Ω
5. In a parallel circuit with two resistors of equal value and
a total current flow of 12 amps, the value of current
through each resistor is ____________ amps.
6. In the following circuit, current flow through R1 is _____
_______ amps, and through R2 is ____________ amps.
24 Volts
R1
R2
10 Ω
15 Ω
180
Review 5
1.
Calculate equivalent resistance for R1 and R2 and total
resistance for the entire circuit.
R1 20 Ω
R3 10 Ω
+
R2 30 Ω
_
R1,R2 equivalent resistance = ____________ Ω
Total resistance =
2.
Ω
Calculate equivalent resistance for R1 and R2 and total
resistance for the entire circuit.
R1 30 Ω
+
_
R3 20 Ω
R2 10 Ω
R1,R2 equivalent resistance = ____________ Ω
Total resistance = ____________
Ω
181
Review 6
1. The rate at which work is done is called
___________ .
2. The basic formulas for power in a DC circuit are:
P = I x __ , P = I2 x __ , and P = _
R
3. In a circuit with a 12 volt supply and 4 W resistance, the
power consumed is ____________ watts.
4. The two characteristics of all magnets are: they attract
and hold ____________ , and, if free to move, they will
assume roughly a ____________ position.
5. Lines of flux always leave the ____________ pole and
enter the ____________ pole.
6. The left-hand rule for conductors states that, when
the ___________ hand is placed on a current-carrying
conductor with the ____________ pointing in the
direction of electron flow, the fingers will point in the
direction of ____________ .
182
Review 7
1.
A ____________ is the graphic representation of AC
voltage or current values over time.
2.
Each phase of three phase AC power is offset by
____________ degrees.
3.
An AC generator produces ____________ cycle(s) per
revolution for each pair of poles.
4.
What is the instantaneous voltage at 240 degrees for a
sine wave with a peak voltage of 150 volts?
5.
What is the effective voltage for a sine wave with a
peak voltage of 150 volts?
183
Review 8
1. The total inductance for this circuit is __________ mh.
4 mh
2 mh
3 mh
L1
L2
L3
1 mh
L4
2.
3.
4.
The total inductance for this circuit is ___________ mh.
L1
L2
5 mh
10 mh
L3
10 mh
The total capacitance for this circuit is __________ mF.
5 µF
10 µF
10 µF
C1
C2
C3
The total capacitance for this circuit is __________ mF.
C1
C2
C3
5 µF
10 µF
10 µF
Review 9
1.
Opposition to current flow in an AC circuit caused by
inductors and capacitors is called ____________ .
2.
Total opposition to current flow in an AC circuit with
both resistance and reactance is called ____________ .
3.
In a 50 hertz circuit, containing a 10 mh inductor, the
inductive reactance is ____________ ohms.
4.
In a purely inductive circuit, ____________
a. current and voltage are in phase
b. current leads voltage by 90 degrees
c. current lags voltage by 90 degrees
5.
In a purely capacitive circuit, ____________
a. current and voltage are in phase
b. current leads voltage by 90 degrees
c. current lags voltage by 90 degrees
6.
In a 50 hertz circuit, containing a 10 microfarad
capacitor, the capacitive reactance is ____________
ohms.
7.
In a circuit with 5 W resistance, and 10 W inductive
reactance, impedance is ____________ ohms.
8.
In a circuit with 5 W resistance, and 4 W capacitive
reactance, impedance is ____________ ohms.
185
Review 10
1.
An AC circuit is ____________ if inductive reactance and
capacitive reactance are equal.
2.
A series AC circuit is ____________ if there is more
inductive reactance than capacitive reactance.
3.
A series AC circuit is ____________ if there is more
capacitive reactance than inductive reactance.
4.
In a 120 VAC, 60 hertz series circuit, with 1000 W
of resistance, 10 mh of inductance and 4 mF of
capacitance, impedance is ____________ W and current
is ____________ amps.
5.
For the following circuit, calculate impedance and
current.
R = 1000 Ω XL = 200 Ω XC = 1200 Ω
120 V
60 Hz
Impedance is __________ W , and It is __________ amps.
6.
For a circuit with a 120 volt AC source and a current of
10 amps, the apparent power is __________VA.
7.
For a circuit with an apparent power of 3000 VA and a
power factor of 0.8, the true power is __________ watts.
186
Review 11
1.
If the primary of a transformer has more turns than the
secondary, it is a ____________ transformer.
2.
If the primary of a transformer has fewer turns than the
secondary, it is a ____________ transformer.
3.
The secondary voltage of an iron-core transformer with
240 volts on the primary, 40 amps on the primary, and
20 amps on the secondary is ____________ volts.
4.
A transformer with a 480 volt, 10 amp primary, and a
240 volt, 20 amp secondary will be rated for
____________ kVA.
5.
A wye connected, three-phase transformer secondary,
with 240 volts line-to-line will have ____________ volts
line-to-neutral.
187
189
Review 1
1.
List the three basic elements of an atom and state
the charge of each (positive, negative, or neutral).
Element
2.
An electron forced out of orbit by an external force is
called a ____________ ____________ .
3.
Conductors allow ____________ free electrons to flow
when an external electric force is applied.
4.
Which of the following materials are good
conductors?
a. copper
b. plastic
c. silver
d. rubber
e.
f.
g.
h.
Charge
aluminum
glass
iron
mica
5.
Semiconductor devices can be manufactured to
allow____________ electrons to flow in one direction
and ____________ electrons to flow in the opposite
direction
6.
What are three good electrical conductors?
A. Copper, gold, mica
B. Gold, silver, wood
C. Gold, silver, aluminum
D. Copper, aluminum, paper
7.
What are four good electrical insulators?
A. Glass, air, plastic, porcelain
B. Glass, wood, copper, porcelain
C. Paper, glass, air, aluminum
D. Plastic, rubber, wood, carbon
8.
What does an electrical insulator do?
A. It lets electricity flow through it in one direction
B. It does not let electricity flow through it
C. It lets electricity flow through it when light shines on it
D. It lets electricity flow through it
9.
The particles that orbit around the center of an atom are
a. Electrons.
b. Molecules.
c. Nucleus.
d. Protons.
10. An atom which loses or gains one electron is called:
a. Balanced.
b. An element.
c. A molecule.
d. A charged particle or ion.
11. The proton carries a single unit positive charge equal in magnitude to the electron charge.
a. True
b. False
12. The electrons attraction to the nucleus is called __________ .
a. electrostatic field
b. electrostatic attraction
c. electrostatic force
d. potential difference
13. Atoms with only one valence electron make good ____________ .
a. Insulators
b. Semiconductors
c. Conductors
d. Resistors
14. The electrons in the outermost shell are called valence electrons.
a. True
b. False
15. An electron has a _______ charge.
a. Positive
b. Negative
c. Neutral
16. In a stable atom, the number of positively charged particles is _______ to the number of negatively charged particles.
a. Equal to
b. Greater than
c. Less than.
17. The positively charged particle of an element is a __________
a. Atom
b. Electron
c. Proton
d. Neutron
18. The center of the atom, the nucleus, is made up of the following
a. Electrons
b. Protons
c. Neutrons
d. All of the answers provided
19. Materials that easily move electrons are:
a. Atoms
b. Conductors
c. insulators resistors
d. all of the answers provided
20. If positive and negative bodies are joined together by a copper wire, the following would happen.
a. An atomic explosion
b. Nothing
c. Electrons would move in the wire from the negative charged body to positive charged body
d. Electrons would move in a wire from the lower charged body to the higher charged body
21. As the number of electrons in the outer orbit increases, the atoms change in behavior from a _________ to a
_________.
a. Conductor / insulator
b. Insulator/ conductor
c. No change either case
22. Which of the following is NOT an insulator?
a. Electrical tape
b. Copper wire
c. Plastic
d. Glass
23. Like charges ___________.
a. Repel
b. Attract
c. have no effect on each other
d. none of the answers provided
24. In which ways can electricity be produced?
a. Chemical - batteries
b. Thermal
c. Photo-electric
d. Magnetically – mechanically generated
e. All of the answers provided
Review 2
1.
Elements are identified by the number of
____________ in orbit around the nucleus.
2.
A material that has an excess of electrons is said to
have a ____________ charge.
3.
A material that has a deficiency of electrons is said
to have a ____________ charge.
4.
Like charges ____________ and unlike charges
____________ .
5.
The force that is applied to a conductor to cause
current flow is ____________ .
6.
Electrons move from ____________ .
a. positive to negative
b. negative to positive
7.
With an increase of length or a decrease of crosssection of a conductor, resistance will ____________ .
a.
b.
increase
decrease
8.
What is electricity?
a. Charged matter.
b. Moving electrons.
c. Positive charge.
d. Negative charge.
9.
What is static electricity?
a. Ionized atoms.
b. Electricity at rest.
c. Charged particles.
d. Attraction and repulsion.
10. Which of the following materials makes the best electromagnet?
a. Copper.
b. Stainless steel.
c. Soft iron.
d. Silver.
11. What is the symbol for alternating current?
a. DC.
c. Hz.
d. F.
e. AC.
12. How did alternating current get its name?
a. From the person who developed it.
b. From the electrons move in one direction and then move back in the other direction.
c. From the constant current.
d. From the constant voltage.
13. Which of the following statements best describes the current Characteristics of an AC system?
a. The electrons move through a circuit in one direction for a period of time, and then move back in the other
direction for a like period of time.
b. The electrons move from a point of low potential to a point of high potential.
c. The voltage in an AC circuit never changes polarity.
d. The electrons move through a circuit in one direction for a period of time, and then move back in the other
direction for a period of time twice as long.
14. What is the name for the flow of electrons in an electric circuit?
A. Voltage
B. Resistance
C. Capacitance
D. Current
15. What is the basic unit of electric current?
A. The volt
B. The watt
C. The ampere
D. The ohm
16. Which instrument would you use to measure electric current?
A. An ohmmeter
B. A wave meter
C. A voltmeter
D. An ammeter
17. What is the name of the pressure that forces electrons to flow through a circuit?
A. Magneto motive force, or inductance
B. Electromotive force, or voltage
C. Farad force, or capacitance
D. Thermal force, or heat
18. What is the basic unit of electromotive force (EMF)?
A. The volt
B. The watt
C. The ampere
D. The ohm
19. How much voltage does an automobile battery usually supply?
A. About 12 volts
B. About 30 volts
C. About 120 volts
D. About 240 volts
20. How much voltage does a wall outlet usually supply (in the Kuwait)?
A. About 12 volts
B. About 30 volts
C. About 120 volts
D. About 240 volts
21. Which instrument would you use to measure electric potential or electromotive force?
A. An ammeter
B. A voltmeter
C. A wave meter
D. An ohmmeter
22. What limits the current that flows through a circuit for a particular applied DC voltage?
A. Reliance
B. Reactance
C. Saturation
D. Resistance
23. What is the basic unit of resistance?
A. The volt
B. The watt
C. The ampere
D. The ohm
24. Which instrument would you use to measure resistance?
A. An ammeter
B. A voltmeter
C. An ohmmeter
D. A wave meter
25. The unit of current is _____________.
a.
b.
c.
d.
ampere
watt
volt
coulomb
26. The device used for measuring potential difference is known as _____________.
a. potentiometer
b. ammeter
c. galvanometer
d. voltmeter
27. The current in a wire ______________.
a.
b.
c.
d.
depends only on the potential difference applied
depends only on the resistance of the wire
depends on both resistance and potential difference
does not depend on resistance and potential difference
28. When there is an electric current passing through a wire, the particles moving are _____________.
a.
b.
c.
d.
electrons
protons
atoms
ions
29. The resistivity of a wire depends on ____.
a.
b.
c.
d.
length
material
area of cross- section
all the above
30. Which effect of current is used in the following appliance?
a. Electric bulb
b. immersion rod
c. electric iron
d. galvanometer
Answer: For electric bulb, immersion rod and electric iron, heating effect of current is used. For galvanometer magnetic effect
of current is used.
31. On what factors does the heating effect of current depend on?
Answer: The heating effect of current depends on

The square of the amount of current flowing

The resistance of the wire and

The time of flow of current
32. Name the instrument that measures the potential difference across the ends of a current carrying conductor. How is
the instrument connected to the circuit?
Answer: Voltmeter measures the potential difference across the ends of a conductor. It is connected in
Parallel across the element, through which current flows due to a certain potential difference.
33. The conventional theory of current flow says that current flows:
a.
b.
c.
d.
Randomly.
Positive to negative.
Negative to positive.
None of the above.
34. The force that causes electrons to flow through a conductor is known as:
a.
b.
c.
d.
The power.
The current.
The voltage.
The resistance.
35. A break or interruption in an electrical circuit is:
a.
b.
c.
d.
An open.
A short.
A ground.
None of the above.
37. The specified voltage output from an electrical device is 0.55 volts. Technician A says this is equivalent to 5.5 millivolts.
Technician B says it is equivalent to 550 millivolts. Who is correct?
a.
b.
c.
d.
Technician A.
Technician B.
Both Technicians A & B.
Neither Technicians A nor B.
38. A material in which there are no free charge carriers is known as
c.
a. conductor
b. insulator
c. Charges
39. The Electrostatic Field is force acting between charged objects that causes them to repel or attract.
a. True
b. False
40. To produce current, the electrons must be moved by a potential difference.
a. True
b.
False
41. Conventional Current Flow is current flow from positive to negative potentials.
a. True
b.
False
42. Electron current, or amperage, is described as the movement of free electrons through a conductor.
a. True
b.
False
43. Resistance is defined as all opposition to current flow.
a. True
b.
False
44. Which of the following is not a basic part of an electric circuit?
a. Fuse
b. Source of Power
c. Load
d. Switch
e. Conductors
45. The units used to measure resistance are ________.
a. Ohms
b. Volts
c. Amps
46. Electrical potential is measured in:
a. Ohms
b. Volts
c. Watts
d. Amps
e. none of the answers provided
47. Using a volt meter, you will get a voltage reading when taking a measurement across an electrical power source.
a. True
b. False
48. Using a volt meter, you will get a voltage reading when taking a measurement across an electrical load.
a. True
b. False
Review 3
1.
The basic Ohm’s Law formula is ____________ .
2.
When solving circuit problems;
current must always be expressed in ____________ ,
voltage must always be expressed in ____________ ,
and resistance must always be expressed in ____________ .
3.
The total current of a simple circuit with a voltage
supply of 12 volts and a resistance of 24 Ω is ____________ amps.
4.
What is the total resistance of a series circuit with
following values: R1=10 Ω, R2=15 Ω, and R3=20 Ω?
____________ Ω.
5.
What is total current of a series circuit that has a 120
volt supply and 60 Ω resistance?
6.
In the following circuit, the voltage dropped across
R1 is ____________ volts and R2 is ____________ volts.
1.5 Ω
R1
+
_
7.
R2
12 Volts
In the following circuit, voltage dropped across R1 is
____________ volts and across R2 is ____________.
5Ω
R1
+
_
8.
1.5 Ω
2Ω
R2
100 Volts
Who discovered that current is directly proportional to the voltage and inversely proportional to the resistance?
a. Kirchhoff.
b. Ampere.
c. Voltaire.
d. Ohm.
9.
What is the applied voltage in a series circuit composed of a battery, and three resistors whose voltage drops are ER1 =
10V, ER2 = 5V, ER3 = 15V. Use Kirchhoff's Voltage Law.
a. 20 V.
b. 25 V.
c. 15 V.
d. 30 V.
10. What is the formula for total current in a series circuit?
a. IT = E1/R1 + E2/R2 + E3/R3.
b. IT = I1 - I2 - I3.
c. IT = I1 + I2 + I3.
d. IT = I1 = I2 = I3.
11. Which of the following statements does not represent ohm's law?
a.
b.
c.
d.
current / potential difference = constant
potential difference / current = constant
potential difference = current x resistance
current = resistance x potential difference
12. The potential difference required to pass a current 0.2 A in a wire of resistance 20 Ω is ____.
a.
b.
c.
d.
100 V
4V
.01 V
40 V
13. The resistance of an electric bulb drawing 1.2 A current at 6.0 V is ___________.
a.
b.
c.
d.
0 .5 Ω
5Ω
0.2 Ω
2Ω
14. Three equal resistances when combined in series are equivalent to 90 Ω. Their equivalent resistance when combined in
parallel will be __________.
a.
b.
c.
d.
270 Ω
30 Ω
810 Ω
10 Ω
15. Ohm's law relates current inversly with ___________.
a.
b.
c.
d.
power
resistance
potential difference
time
16. State ohm's law.
Answer: When temperature and other physical parameters remain constant, the current flowing
through a conductor is directly proportional to the potential difference across its ends.
17. Which of the following graphs depict ohm's law?
Answer: Graph (a) represents ohm's law since a straight line which shows that 'I' is directly proportional to 'V'.
18. The sum of voltage drops in a series circuit equals the:
a.
Voltage across the largest load.
b. Voltage across the smallest load.
c.
Source voltage.
d. Shunt circuit voltage.
19. The relationship between voltage (V), current (I) and resistance (R) for a resistor is:
a. V = IR
b. V = R/I
c. V = IR * R
20. A potential difference of 7.5 V appears across a 15-ohm resistor. Which of the following is the current through the
resistor?
a. 0.25 A
b. 0.5 A
c. 2 A
21. In 1827, George Simon Ohm discovered that there was a definite relationship between voltage, current, and resistance
in an electrical circuit.
a. True
b. False
22. In the formula for Ohms law, what does the letter E stands for?
a. Volts
b. Ohms
c. Amps
23. In the formula for Ohms law, what does the letter I stands for?
a. Volts
b. Ohms
c. Amps
24. In the formula for Ohms law, what does the letter R stands for?
a. Volts
b. Ohms
c. Amps
25. Using the above formula for ohms law, write the equation for finding Volts
a. E = I x R
b. E = I / R
c. E = R / I
26. Using the above formula for ohms law, write the equation for finding Current
a. I = E / R
b. I = E x R
c. I = R/E
27. Using the above formula for ohms law, write the equation for finding Resistance
a. R = E / I
b. R = E x I
c. R= I/E
28. Given E = 208 volts, R = 121 ohms, I = ______
a. 1.7 amps
b. 0.58 amps
c. 25.2 amps
d. none of the answers provided
29. Given: R = 10 ohms, I= 48 amps, what is the voltage?
a. 480v
b. 208v
c. 240v
d. 120v
30. Given: Voltage = 120 volts, Amps = 15, R = _______
a. 80 ohms
b. 8 ohms
c. 1800 ohms
d. none of the answers provided
31. In a series circuit, how many paths are there for current to flow?
a. One Path
b. Two separate paths
c. 3 separate paths
Review 4
1. The total resistance of a parallel circuit that has four
20 Ω resistors is ____________ Ω.
2. Rt for the following circuit is ____________ Ω.
R2
R2
10 Ω
20 Ω
R1
R2
5Ω
10 Ω
R3
30 Ω
3. Rt for the following circuit is ____________ Ω.
4. Voltage available at R2 in the following circuit is
____________ volts.
12 Volts
R1
R2
5Ω
10 Ω
R1
R2
10 Ω
15 Ω
5. In a parallel circuit with two resistors of equal value and
a total current flow of 12 amps, the value of current
through each resistor is ____________ amps.
6. In the following circuit, current flow through R1 is _____
_______ amps, and through R2 is ____________ amps.
24 Volts
7.
What is the formula for Kirchhoff's current for a circuit with three parallel resistors?
a. IT = I1 = I2 = I3.
b. IT = E/R.
c. IT = I1 + I2 + I3.
8.
What is the formula for two or more unlike resistors in parallel?
a. RT = E/R1.
b. RT = R1/N.
c. 1/RT = 1/R1+1/R2+1/R3
9.
Two coils have a combined resistance of 25 when connected in series and a resistance of 4 when connected in parallel.
What is the resistance of each coil?
R 1 and R 2 , and R s represents resistances in series and R p represents
Answer: Let the resistance be
resistance in parallel.
According to the given data
R 1 +R 2 =R S =25
+
_______( 1)
=
=
_______( 2)
R 1 + R 2 = 25
R 1 R 2 = 100
2
2
(R 1 - R 2 ) = (R 1 + R 2 ) - 4 R 1 R2
2
= 25 - 4 (100)
= 625 - 400
= 225
R 1 - R 2 = 15
R 1 + R 2 = 25
Adding
2R 1 = 40
R 1 = 20
R2=5
10. Four cells each of e.m.f = 'E' are joined in parallel to form a battery. The equivalent e.m.f of the battery will be
_______.
a.
b.
c.
d.
4E
E
E/4
E=0
Answer: c
11. When are several resistors in a circuit said to be connected in parallel?
Answer: Several resistors are said to be connected in parallel when the potential difference across the resistors remain the
same.
12. Two identical lamps are connected in parallel to a 12-volt source. The voltage across each lamp is:
a.
b.
c.
d.
12 volts.
6 volts.
4 volts.
2 volts.
13. In a parallel circuit which of the following is true:
a.
b.
c.
d.
Circuit resistance decreases as additional branches are added.
Current is equal in all parts of the circuit.
Only one current path to ground.
None of these
14. Several lamps are connected in parallel to a voltage source. If one light burns out, all the other lamps:
a.
b.
c.
d.
Will go out.
Will get brighter
Will not be affected.
Will get dimmer.
15. In a Parallel circuit, how many paths are there for current to flow?
a. One Path
b. Two or more separate paths
16. What is the formula for Kirchhoff's current for parallel circuits?
a. IT = I1 = I2 = I3.
b. IT = E/R.
c. IT = I1 + I2 + I3.
d. IT = I1 2 + I2.
Review 5
1.
Calculate equivalent resistance for R1 and R2 and total
resistance for the entire circuit.
R1 20 Ω
R3 10 Ω
+
_
R2 30 Ω
R1,R2 equivalent resistance = ____________ Ω
Total resistance = ____________ Ω
2.
Calculate equivalent resistance for R1 and R2 and total
resistance for the entire circuit.
R1 30 Ω
+
_
R3 20 Ω
R2 10 Ω
R1,R2 equivalent resistance = ____________ Ω
Total resistance = ____________ Ω
3.
Three resistors 2 Ω, 3 Ω and 4 Ω are connected so that the equivalent resistance is 9 Ω.
The resistors are connected _________.
a. all in series
b. all in parallel
c. 2 Ω and 3 Ω in parallel and the combination in series with 4 Ω
d. 2 Ω and 3 Ω in series and the combination in parallel to 4 Ω
4.
In the figure,
a. 6 Ω, 3 Ω and 9 Ω are in series
b. 9 Ω and 6 Ω are in parallel and the combination is in series with 3 Ω
c. 3 Ω, 6 Ω and 9 Ω are in parallel
d. 3 Ω, 6 Ω are in parallel and 9 Ω is in series
5.
The resistance across AB is
a.
b.
c.
d.
6.
4Ω
1Ω
2Ω
0.5 Ω
A series/parallel circuit is represented by illustration _______.
a. 1
b. 2
c. 3
7.
A parallel circuit is represented by illustration ____.
a. 1
b. 2
c. 3
8.
A series circuit is represented by illustration _____.
a. 1
b. 2
c. 3
9.
A fuse is added to the circuit to protect the circuit and the other loads.
a. True
b. False
Review 6
1. The rate at which work is done is called
___________ .
2.
The basic formulas for power in a DC circuit are:
P = I x __
2
P = I x __
_
P=
R
3.
In a circuit with a 12 volt supply and 4 Ω resistance, the
power consumed is ____________ watts.
4.
The two characteristics of all magnets are: they attract
and hold ____________ , and, if free to move, they will
assume roughly a ____________ position.
5.
Lines of flux always leave the ____________ pole and
enter the ____________ pole.
6.
The left-hand rule for conductors states that, when
the ___________ hand is placed on a current-carrying
conductor with the ____________ pointing in the
direction of electron flow, the fingers will point in the
direction of ____________ .
7.
What is one important characteristic of magnetic lines of force?
a. Magnetic lines of force are conducted by all materials.
b. Magnetic lines of force are conducted by some materials.
c. Magnetic lines of force move perpendicular to each other.
d. Magnetic lines of force are attracted by air.
8.
What is the unit of electrical power?
a. Watt.
b. Ampere.
c. Ohm.
d. Volt.
9.
What current would flow through a 5,000 Ωresistor that is dissipating 50 W of power?
a. 100 mA.
b. 101 A.
c. 10 mA.
d. 100 A.
10. A schematic shows five (5) identical resistors connected in parallel across a 230 Vac source as an anticondensation heater for a large motor. The instruction manual states that the entire anti-condensation heater
circuit requires 350 watts. What should be the value of each of the resistors:
a. 30 ohms
b. 151 ohms
c. 327 ohms
d. 755 ohms
11. Which of the following is another name for the magnetic lines of force?
a. CEMF.
b. EMF.
c. Flux.
d. Conductor.
12. A passenger cabin has 110 passenger reading lamps each rated at 10W, 28V. What is the maximum load current
imposed by these lamps?
a. 25.5 A
b. 39.3 A
c. 308 A
13. When a current 'I' flows through a resistance 'R' the electrical Power is given by ___________.
a. I R
2
b. I R
2
c. I R
d. I 2 / R
14. Kilowatt - hour is the unit of ______________.
a. potential difference
b. electric power
c. electrical energy
d. charge
15. When a fuse is rated 8 A, it means _____________.
a.
b.
c.
d.
it will not work if current is less than 8 A
it has a resistance of 8 W
it will work only if current is 8 A
it will melt if current exceeds 8 A
16. The work done in moving a unit positive charge across two points in an electric circuit is a measure of ___________.
a. current
b. potential difference
c. resistance
d. Power
17. Joule / Coulomb is same as ______________.
a.
b.
c.
d.
Watt
Volt
ampere
Ohm
18. The strength of the magnetic field that surrounds a single conductor with current flowing though it?
a. Is usually weak.
b. Varies directly with the amount of current flowing through the conductor.
c. Can be detected using a magnetic compass.
d. All of these.
19. When the lines of a magnetic force cut across a conductor:
a. A voltage is induced into the conductor.
b. The conductor is permanently induced.
c. The conductor is permanently magnetized.
d. Magnetism is induced into the conductor.
20. Which of the following factors does NOT affect the strength of an electromagnet?
a. The type of core.
b. The direction of the windings.
c. The amount of current flow.
d. The number of turns in the coil.
21. When electrical current is passed through a conductor that is forced into many loops, a magnetic field is created. The
strength of the field may be increased by
a. Increasing the turns or coils of the conductor.
b. Increasing the amount of the current in the coils.
c. Both A and B.
d. Neither A nor B.
22. Magnets are surrounded with lines of force that are called flux.
a. True
b. False
23. Two positive magnetic poles attract each other.
a. True
b. False
24. As the current increases in a wire, the strength of the magnetic field
a. decreases
b. does not change
c. increases
d. is not influenced by current flow
25. If you reverse the current flow in a wire the magnetic lines of force will not rotate in the opposite direction.
a. True
b. False
26. When a wire is moved through a magnetic field, electricity flows in the wire.
a. True
b. False
+
24V
33Ω
15Ω
figure 01
27. What is the electric power supplied by the battery shown in figure 01:
a. 24 W
b. 48 W
c. 0.5 W
d. 12 W
0.033Ω
120Vac
60 Hz
1.25Ω
1.25Ω
0.033Ω
figure 02
28. What is the total power consumed by the four resistors shown in figure 02
a. 23 kW
b. 21 kW
c. 2100 W
d. kW
29. An SOV has a coil rating of 120 Vdc, 35 W. An ohmmeter is used to check the coil
resistance. The value should be:
a. about 410 ohms
b. about 3.4 ohms
c. much less than 410 ohms; due to inductive reactance
d. much greater than 410 ohms; due to inductive reactance
30. What is one important characteristic of magnetic lines of force?
a. Magnetic lines of force are conducted by all materials.
b. Magnetic lines of force are conducted by some materials.
c. Magnetic lines of force move perpendicular to each other.
d. Magnetic lines of force are attracted by air.
31. Which of the following materials makes the best electromagnet?
a. Copper.
b. Stainless steel.
c. Soft iron.
d. Silver.
32. What is the unit of electrical power?
a. Watt.
b. Ampere.
c. Ohm.
d. Volt.
33. What current would flow through a 5,000-Ω resistor that is dissipating 50 W of power?
a. 100 mA.
b. 101 A.
c. 10 mA.
d. 100 A.
34. Which of the following is another name for the magnetic lines of force?
a. CEMF.
b. EMF.
c. Flux.
d. Conductor.
35. A 200 V 40 KVA ac generator has an output current of 200 amps at a phase angle of 60 degrees lagging. Find the true
Power?
a. 20 K W
b. 8 KW
c. 40 KW
Review 7
1.
A ____________ is the graphic representation of AC
voltage or current values over time.
2.
Each phase of three phase AC power is offset by
____________ degrees.
3.
What is the name of all values of the sine wave between 0 and 180 above the zero reference line?
a. One cycle.
b. Positive alternation.
c. Negative alternation.
d. One revolution.
An AC generator produces ____________ cycle(s) per
revolution for each pair of poles.
4.
5.
6.
o
o
Decreasing the current in the field coil of a DC generator will:
a. decrease the output voltage
b. increase the output voltage
c. increase the output frequency
What is the instantaneous voltage at 240 degrees for a
sine wave with a peak voltage of 150 volts?
7.
What is the effective voltage for a sine wave with a
peak voltage of 150 volts?
8.
What happens to the wavelength of an AC cycle if the frequency increases?
a. Increases.
b.Decreases.
c. Remains the same.
d.Doubles.
9.
What is the formula used to find the peak voltage of 100 volts effective?
a. Peak voltage = .707 x 100 Veff.
b.Peak voltage = .9 x 100 Veff.
c. Peak voltage = 1.414 x 100 Veff.
d.None of the above.
10. Which of the following is another name used when referring to the RMS (Root-Mean-Square) value?
a. Peak value.
b.Effective value.
c. Peak-to-peak value.
d.Average value.
11. What is the effective value of 200 volts peak-to-peak?
a. 70.7 Veff.
b.141.4 Veff.
c. 14.14 Veff.
d.707.0 Veff.
12. A device that produces a voltage using chemical reaction is:
a. a battery.
b.a generator.
c. a solar cell.
d.a crystal.
13. The law of magnetism states that like magnetic poles repel and unlike magnetic poles attracts.
a. True
b.False
14. The group of magnetic field lines emitted outward from the north pole of a magnet is called magnetic flux.
a. True
b.False
15. The flow of AC electricity changes direction during a cycle.
a. True
b.False
16. In generating electricity, an armature coil is needed. The armature coil is
a. A rotating loop of wire
b.A stationary loop of wire
c. A rotating magnet
d.A stationary magnet
17. The maximum voltage generated is found at ______ degrees in the position of the armature vs. the magnetic poles.
a. Zero
b.45
c. 90
d.180
18. Voltage measured in a home is about 70% of the peak voltage that is generated.
a. True
b.False
19. The peak-to-peak voltage measured is 680 volts. The RMS value of this voltage is:
a. 120 volts
b. 240 volts
c. 208 volts
d. 480 volts
20. What happens to the wavelength of an AC cycle if the frequency increases?
a. Increases.
b.Decreases.
c. Remains the same.
d.Doubles.
21. What is the formula used to find the peak voltage of 100 volts effective?
a. Peak voltage = .707 x 100 Veff.
b.Peak voltage = .9 x 100 Veff.
c. Peak voltage = 1.414 x 100 Veff.
d.None of the above.
22. Which of the following is another name used when referring to the RMS (Root-Mean-Square) value?
a. Peak value.
b.Effective value.
c. Peak-to-peak value.
d.Average value.
23. What is the effective value of 200 volts peak-to-peak?
a. 70.7 Veff.
b.141.4 Veff.
c. 14.14 Veff.
d.707.0 Veff.
24. What is the instantaneous value of current at 90 degrees of a sine wave whose peak value is 200 amps?
a. 100 A
b.0
c. 200 A
25. A voltage waveform has a peak value of 100 V. What is the average value( RMS )?
a. 63.7 V
b.70.7 V
c. 50 V
26. A voltage waveform has RMS value of 70.7 volts. What is the peak to peak value of the waveform?
a. 50 V
b.100 V
c. 200 V1
27. The magnitude of the emf generated in simple generator depends on the followings:
a. The flux density of the magnetic field (Tesla) only
b.The flux density and the length of the conductor in the field (meter) only
c. The flux density, the length and the velocity (speed) of the conductor(meter/sec) moving through the field
Answer: c
28. An aircraft supply has an RMS value of 115 V. Which one of the following gives the approximate peak value of the
supply voltage?
a. 67.5 V
b. 115 V
c. 163 V
29. The peak value of current supplied to an aircraft is 28 A. Which one of the following gives the approximate value of
RMS current supplied?
a. 10 A
b. 14 A
c. 20 A
30. A single-phase AC generator has twelve poles and it runs at 600 rpm. Which of the following gives the output frequency
of the generator?
a. 50 Hz
b. 60 Hz
c. 120 Hz
31. The slip rings in an AC generator provide a means of:
a. connecting an external circuit to a rotating armature winding
b. supporting a rotating armature without the need for bearings
c. periodically reversing the current produced by an armature winding
32. A sinusoidal voltage of 40 V peak-to-peak flows in a circuit. What is the RMS value of the voltage?
a. 14.12 V
b. 13 V
c. 10.5 V
Review 8
1.
The total inductance for this circuit is __________ mh.
4 mh
2 mh
3 mh
1 mh
L2
L3
L4
L1
2.
3.
The total inductance for this circuit is ___________ mh.
L1
L2
5 mh
10 mh
The total capacitance for this circuit is __________ mF.
5 µF 10 µF
C1
4.
C2
10 µF
C3
. mF
The total capacitance for this circuit is __________
C1
C2
C3
5 µF
10 µF
10 µF
L3
10 mh
5.
Which of the following statements best describes capacitance?
a. The opposition the capacitor offers to voltage.
b. The capacitor's ability to store energy.
c. The opposition the capacitor offers to current.
d. The capacitor's ability to store resistance.
6.
What factors determine the capacitance of a capacitor?
a. Area of the plates and thickness of the dielectric.
b. Area of the plates and the length of the dielectric.
c. Distance between the plates only.
d. Type of dielectric used only.
7.
What is the total capacitance of a circuit with three capacitors connected in series with the following values, C1 = .015
fd, C2 = .015 fd, and C3= .015 fd?
a. .5 fd.
b. .05 fd.
c. .015 fd.
d. .005 fd.
What is the total capacitance of a circuit containing a .01 fd, a .015 fd, and a .001 fd capacitor, all connected in parallel?
a. .035 fd.
b. .06 fd.
c. .026 fd.
d. .0026 fd.
8.
9.
What is the inductance of a circuit containing two 10 mh inductors connected in parallel?
a. 20 mh.
b. 10 mh.
c. 5 mh.
d. 15 mh.
10. What is the total inductance of a circuit containing three 5 mh inductors connected in series?
a. 5 mh.
b. 15 mh.
c. 1.67 mh.
d. d. 10 mh.
U
5 H each
V
figure 05
13. Each of the inductors shown in figure 05 has a 5 H value, what is the effective total
inductance:
a.
b.
c.
d.
0.2 H
1H
5H
25 H
5H
5H
A
5H
5H
B
figure 06
14. The effective inductance exhibited by the circuit shown in figure 06 is:
a.
b.
c.
d.
H
8.3 H
6.5 H
5.7 H
5K
2.5F
5K
figure 08
15. The time constant of the circuit shown in figure 08 is:
a.
b.
c.
d.
25 sec
usec
0.025 sec
0.25 sec
SW-1
100 Vdc
R
C
figure 09
16. For the circuit shown in figure 09, after SW-1 is closed the voltage across the capacitor
after one time constant has passed is:
a.
b.
c.
d.
63 volts
37 volts
100 volts
0 volts
17. What is the phase relationship of the current and voltage in a pure inductive circuit?
a. The current leads voltage by 90o.
b. The current lags voltage by 90o.
c. The current leads voltage by 45o.
d. The current lags voltage by 45o.
18. What is the inductance of a circuit containing two 10 mh inductors connected in parallel?
a. 20 mh.
b. 10 mh.
c. 5 mh.
d. 15 mh.
19. What is the total inductance of a circuit containing three 5 mh inductors connected in series?
a. 5 mh.
b. 15 mh.
c. 1.67 mh.
d. 10 mh.
20. What happens to the current in purely inductive circuit when the frequency is increased?
a. Current will increase
b. Current will decrease
c. No change of value of current
Review 9
1.
Opposition to current flow in an AC circuit caused by
inductors and capacitors is called ____________ .
2.
Total opposition to current flow in an AC circuit with
both resistance and reactance is called ____________ .
3.
In a 50 hertz circuit, containing a 10 mh inductor, the
inductive reactance is ____________ ohms.
4.
In a purely inductive circuit, ____________
a. current and voltage are in phase
b. current leads voltage by 90 degrees
c. current lags voltage by 90 degrees
5.
In a purely capacitive circuit, ____________
a. current and voltage are in phase
b. current leads voltage by 90 degrees
c. current lags voltage by 90 degrees
6.
In a 50 hertz circuit, containing a 10 microfarad
capacitor, the capacitive reactance is ____________ ohms.
7.
In a circuit with 5 Ω resistance, and 10 Ω inductive
reactance, impedance is ____________ ohms.
8.
In a circuit with 5 Ω resistance, and 4 Ω capacitive
reactance, impedance is ____________ ohms.
9.
What is the capacitive reactance of a capacitor valued at .05 µfd when a 5kHz signal is applied?
a. 6363.1 Ω.
b. 636 Ω.
c. 122 Ω.
d. 235 Ω.
10. What is the inductive reactance of a circuit containing an inductor valued at 15 mh, with a 10kHz signal applied?
a. 942 Ω.
b. 9843 Ω.
c. 98 Ω.
d. 9042 Ω.
11. What is the inductive reactance of a circuit containing an inductor valued at 15 mh, with a 10kHz signal applied?
a. 942 Ω.
b. 9843 Ω.
c. 98 Ω.
d. 9042 Ω.
12. If the voltage applied to a pure inductive circuit is 100 volts and the current is5 amps, what is the inductive reactance
of the circuit?
a. 0.05 ohms
b. 20 ohms
c. 500 ohm
13. Find the inductive reactance of a pure inductor if the supply frequency is 1kHzand the inductance is 1 MH.
a. 6.28 Ohm
b. 0.166 Ohm
c. 166 Ohm
14. What is the applied voltage to a resistive-capacitive circuit if the voltage drop across the resistor is 15 V and the
voltage drop across the capacitor is 20 V?
a. 10 V.
b. 15 V.
c. 20 V.
d. 25 V.
15. What is the total impedance of a circuit when the resistance is 15K Ω and the capacitive reactance is 10K Ω?
a. 18K Ω.
b. 1.8K Ω.
c. 180 Ω.
d. 180K Ω.
11. The power factor in an AC circuit is the same as:
a. the sine of the phase angle
b. the sine of the phase angle
c. the tangent of a phase angle
12. An AC load has a power factor of 0.8. What is the true power dissipated in the load if it consumes a current of 2 A at
100V?
a. 180 W
b. 160 W
c. 200 W
13. A resistor of 120 ohms is connected in series with a capacitive reactance of 160 ohms. What is the current flowing
when the circuit is connected to a 200 VAC supply?
a. 1 A
b. 0.5 A
c. 0.8 A
5uF
5uF
C
5uF
5uF
D
figure 07
18. The total effective capacitance exhibited by the circuit shown in figure 07 is:
a.
b.
c.
d.
uF
0.133 uF
2.5 uF
3.0 uF
19. If an 8 uF capacitor, rated at 660 Vac is placed directly across a 230 Vac 50 Hz circuit, the resulting
current through the circuit is:
a.
b.
c.
d.
3.98 amps
0.58 amps
1.15 amps
1.99 amps
20. Which of the following statements best describes capacitance?
a. The opposition the capacitor offers to voltage.
b. The capacitor's ability to store energy.
c. The opposition the capacitor offers to current.
d. The capacitor's ability to store resistance.
21. What factors determine the capacitance of a capacitor?
a. Area of the plates and thickness of the dielectric.
b. Area of the plates and the length of the dielectric.
c. Distance between the plates only.
d. Type of dielectric used only.
22. What is the total capacitance of a circuit with three capacitors connected in series with the following values, C1 = .015
μfd, C2 = .015 μfd, and C3 = .015 μfd?
a. .5 μfd.
b. .05 μfd.
c. .015 μfd.
d. .005 μfd.
23. What is the total capacitance of a circuit containing a .01 μfd, a .015 μfd, and a .001 μfd capacitor, all connected in
parallel?
a. .035 μfd.
b. .06 μfd.
c. .026 μfd.
d. .0026 μfd.
24. What is the capacitive reactance of a capacitor valued at .05 μfd when a 5kHz signal is applied?
a. 6363.1 Ω.
b. 636 Ω.
c. 122 Ω.
d. 235 Ω.
25. What happens to the current in purely capacitive circuit when the frequency is increased?
a. Current will decrease
b. Current will increase
c. Current remain the same
26. If the voltage applied to a pure capacitive circuit is 50 volts and the current is 2amp, what is the capacitive reactance of
the circuit?
a. 100 Ohm
b. 25 Ohm
c. 0.04 Ohm
27. Find the capacitive reactance of a pure inductive circuit if the supply frequency is 10 kHz and the capacitance is 1uF?
a. 15.9 ohm
b. 0.62 ohm
c. 10 ohm
28. In purely capacitive circuit, the current ________ the voltage by ________degrees.
a. Lags, 90
b. Leads, 45
c. Leads, 90
Review 10
1.
An AC circuit is ____________ if inductive reactance and
capacitive reactance are equal.
2.
A series AC circuit is ____________ if there is more
inductive reactance than capacitive reactance.
3.
A series AC circuit is ____________ if there is more
capacitive reactance than inductive reactance.
4.
In a 120 VAC, 60 hertz series circuit, with 1000 Ω
of resistance, 10 mh of inductance and 4 mF of
capacitance, impedance is ____________ Ω and current
is ____________ amps.
5.
For the following circuit, calculate impedance and
current.
R = 1000 Ω
XL = 200 Ω
XC = 1200 Ω
120 V
60 Hz
Impedance is __________ Ω, and It is __________ amps.
6.
For a circuit with a 120 volt AC source and a current of
10 amps, the apparent power is __________VA.
7.
For a circuit with an apparent power of 3000 VA and a
power factor of 0.8, the true power is __________ watts.
8.
In the diagram below determine the current and the voltage drops.
9.
In the diagram below determine the currents, using three methods of calculation. If your calculations are correct, you
should obtain three times the same value for the total current.
10. Find the impedance in the figure below.
11. Calculate the current and the voltage drops in the following diagram, check your answers by adding the voltages
together.
12. Express the impedance of the circuit below.
13. Is the circuit in the previous question 12 more capacitive or more inductive? Explain.
14. For the circuit given in question 12 find all currents. Double check your work by finding the total current using the
total impedance.
1K
1K
240 Vac
60 Hz
33uF
figure 10
15. What is the reactance/resistance/impedance (read carefully) of the circuit shown in figure 10:
a.
b.
c.
d.
80/2000/2002 ohms
80/2000/80 ohms
40/2000/80 ohms
80/2000/500 ohms
16. If the voltage leads the current by 30 degrees, the power factor is:
a.
b.
c.
d.
0.86 lagging
0.86 leading
0.5 lagging
0.5 leading
17. What is the applied voltage to a resistive-capacitive circuit if the voltage drop across the resistor is 15 V and the
voltage drop across the capacitor is 20 V?
a. 10 V.
b. 15 V.
c. 20 V.
d. 25 V.
18. What is the total impedance of a circuit when the resistance is 15K Ω and the capacitive reactance is 10K Ω?
a. 18K Ω.
b. 1.8K Ω.
c. 180 Ω.
d. 180K Ω.
19. A coil has a pure inductance value of 0.159 H and a resistance of 100 ohms and is connected to a 240 V 50 Hz supply.
What is the impedance of the coil?
a. 159 Ohm
b. 112 Ohm
c. 7950 Ohm
20. A 15.9uF capacitor and a 100 ohms resistor are connected in series across a240 V 50 Hz supply. Calculate the circuit
impedance?
a. 50 ohm approximately
b. 100 ohms approximately
c. 224 ohms approximately
21. The ratio of TRUE POWER to APPARENT POWER is termed POWER FACTOR. If a 40 KVA generator produces a power
output of 30 KW, what is the Power Factor of the generator?
a. 0.75
b. 1.33
c. 0.8
Review 11
1.
If the primary of a transformer has more turns than the
secondary, it is a ____________ transformer.
2.
If the primary of a transformer has fewer turns than the
secondary, it is a ____________ transformer.
3.
The secondary voltage of an iron-core transformer with
240 volts on the primary, 40 amps on the primary, and
20 amps on the secondary is ____________ volts.
4.
A transformer with a 480 volt, 10 amp primary, and a
240 volt, 20 amp secondary will be rated for
____________ kVA.
5.
A wye connected, three-phase transformer secondary,
with 240 volts line-to-line will have ____________ volts
line-to-neutral.
6.
A certain transformer has 250 turns in its primary winding. In order to double the voltage, how many turns must be
on the secondary winding?
7.
In the figure below determine Is. What is the value of RL?
8.
Determine each unknown voltage indicated in the figure
9.
A transformer has 2400 primary turns and 600 secondary turns. If the primary is supplied from a 220 VAC supply,
which one of the following gives the resultant secondary voltage?
a.
d. 55 V
b.
e. 110 V
c.
f. 880 V
10. A transformer has 2000 primary turns and 120 secondary turns and turn ratio of 4:1. What is the output power?
a.
a. 240 kVA
b.
b. 100 kW
c.
c. 60 kVA
11. A transformer has a turns-per-volt rating of 1.2. How may turns are required to produce secondary output of 50 V?
d.
a. 50 turns
e.
b. 60 turns
f.
c. 100 turns
12. A transformer has 1200 primary turns and 60 secondary turns. Assuming that the transformer is loss-free, what is the
primary current if the load current of 20 A is taken from the secondary?
a. 1 A
b. 0.5 A
c. 2 A
13. A transformer produces an output voltage of 100 V under no-load conditions and an output voltage of 101 V when a
full load is applied. What is the percent regulation?
a. 5 %
b. 8 %
c. 10 %
14. A three phase transformer bank is composed of three single-phase transformers having a primary
voltage of 4800 Vac and a secondary voltage of 2400 Vac. If the transformers are connected wyedelta to a 4160 Vac source, the line-to-line voltage on the secondary is:
a.
b.
c.
d.
2400 Vac
4160 Vac
3600 Vac
1200 Vac
15. A transformer is wound with 100 turns on the primary and 450 turns on the secondary. The primary is connected to
250 volts ac supply. Find the secondary voltage?
a. 1125 volts
b. 55.5 volts
c. 112500 Volts
Answer: a
16. Transformer losses are due to Iron losses and copper losses. Iron losses are due to eddy current and hysteresis losses.
Eddy current losses are reduced by ____________and hysteresis losses by _______of low hysteresis loss.
a. Laminating core material, choosing correct material
b. Using solid metal core, not using material
c. Laminating iron core, using material such as silicon steel