DC CIRCUIS EXCEL SOURCE Flashcards
PROBLEMS AND OBJECTIVE TYPE QUESTIONS
If a complex circuit is reduced to an equivalent circuit consisting of a single voltage source in series with a single resistor, this is an example of:
Thevenin`s theorem
Two equal resistors when connected in series across a supply draws a total power of 20 watts. What is the total power drawn when the two resistors are connected in parallel across the same supply?
20 W
Assuming a power source to have a fixed value of internal impedance, maximum power will be transferred to the load when:
The load impedance equals the internal impedance of the source.
Two resistors x and y are connected in parallel. Resistor x having a value of 6 ohms while resistor y being adjustable over a wide range. The parallel combination is then connected through a 2 – ohm line resistor to a 120 V DC source. For what resistance y will its power be the greatest?
1.5 Ω
A load is connected to a network. At terminals to which the load is connected, Rth = 10 Ω and Vth = 40 V. The maximum possible power supplied to the load is:
40 W
An ampere is how many abampere?
0.1
If a complex circuit is reduced to an equivalent circuit consisting of a single current source in parallel with a single resistor, this is an example of:
Norton`s theorem
In any closed loop in a network, the algebraic sum of the voltage drops (i.e. products of current and resistance) taken around the loop is equal to the resultant e.m.f. acting in that loop. This is known as:
Voltage law
In any network made up of linear resistances and containing more than one source of e.m.f., the resultant current flowing in any branch is the algebraic sum of the currents that would flow in that branch if each source was considered separately. What is this theorem?
Superposition theorem
The current in any branch of a network is that which would result if an e.m.f. equal to the p.d. across a break made in the branch, were introduced into the branch, all other e.m.f.’s being removed and represented by the internal resistances of the sources.
Thevenin`s theorem
The power transferred from a supply source to a load is at its maximum when the resistance of the load is _______ the internal resistance of the source.
equal to
The terminal voltage of a battery is 11.8 V when delivering 20W of power to an external load resistor R. If the battery has an emf of 15V, find the internal resistance of the battery.
1.89 Ω
Three series resistors A, B and C are connected across a 120 – V supply. If the resistor A = 50 ohms and the voltage across resistor B = 40V. when the current is ½ A. what is the resistance in resistor C in ohms?
110 Ω
Under the conditions of maximum power transfer, a voltage source is delivering a power of 15 W to the load. What is the power generated by the source?
30 W
What is the efficiency for maximum power transfer?
50%
What is the first step in Norton’s theorem?
Short the load under test
What is the first step in Thevenin’s theorem?
Open the load under test
A conductor whose diameter is 0.175 inch has a resistance of 0.5 ohm. The wire is drawn through a series of dies until its diameter is reduced to 0.08 inch. Assuming the specific resistance of the material remains constant, what is the resistance of the lengthened conductor?
11.45 Ω
In a voltage divider network, the total resistance
Should be as small as the power supply will allow
Two (2) 115-V incandescent lamps A and B are connected in series across a 230-V source. If lamp A is rated at 75 watts and lamp B is rated 50 watts, determine the current by the series connection.
0.52 A
A process equipment contains 100 gallons of water at 25°C. It is required to bring it to boiling point in 10 minutes. The heat loss is estimated to be 5%. What is the kW rating of the heater?
208.47
The resistance of a transformer winding is 0.25 ohm at 25°C. When operating at full load, the temperature of the winding is 75°C. The temperature coefficient of resistance for copper is 0.00427 per °C. What is the winding resistance at full load?
0.298 Ω
Resistors are identified as to wattage by:
size
Derived units are obtained from various combinations of ______.
fundamental units
Good engineering practice usually requires that a series-parallel resistive network be made:
From resistors that are all the same.
How much heat in kcal is produced by a current of 20 Amperes flowing for half of an hour in a circuit having a resistance of 6 ohms?
1032
The resistance of a copper wire at 30°C is 50 ohms. If the temperature coefficient of copper at 0°C is 0.00427°C^-1, what is the resistance at 100°C?
63.25
A copper bar is 1/2 inch by 4 inches by 20 feet. If the resistivity of the copper bar is 10.37 ohms-cmf, then what is the resistance of the copper bar?
8.1445 x 10ˉ⁵ Ω
If the reference point is changed to the earth point, then any voltage taken w.r.t. the earth is known as ____.
absolute potential
If a 220 V heater us used on 110 V supply, heat produced by it will be ____ as much
one-fourth
A wire with a smaller cross-sectional area will produce:
more heat
For a given line voltage, four heating coils will produce maximum heat when connected:
All in parallel
You have an unlimited supply of 1-W, 100-Ω resistors. You need to get a 100-Ω, 10-W resistor. This can be done most cheaply by means of a series-parallel matrix of:
4 x 4 resistors
Scientific notation is a method _____.
all of the choices
What is the size of 250MCM in square millimeter?
126.677
Four wires of same material, same cross – sectional area and same length when connected in parallel gives a resistance of 0.25 ohm. If the same four wires are connected in series, its effective resistance will be equal to ____.
4 ohms
A carbon resistor dissipates 60 watts of power from a 120-volt source at 20°C. How much power will be dissipated in the resistor at 120°C if connected across the same source? Assume that the temperature coefficient of carbon at 20°C is – 0.0005 per °C.
63.16 W
The power taken by a 500-ft resistive coil made of copper wire is 250 watts at 100 volts. The resistivity of copper is 10.4 ohm-cm per ft. Calculate the cross-sectional area of the coil in circular mil.
107
A 500 MCM ACSR cable has 37 strands. Determine the diameter in mils of each strand.
116.25
The resistance of two wires is 25 ohms when connected in series and 6 ohms when joined in parallel. The resistance of each wire is ____.
15 ohms and 10 ohms
Suppose you double the voltage in a simple dc circuit and cut the resistance in half. The current will become:
Four times as great
In a series-connected string of holiday ornament bulbs, if one bulb gets shorted out, which of these is most likely?
The current in the string will go up.
The presence of electric current is
only made known by the effect if
produces. Three important effects
are:
C. generation, chemical & electric
shock
It is a cell designed to produce
electric current and can be
recharged.
A. Secondary cell
Which is the best conductor of
electricity?
A. Aluminum
B. Silver
C. Copper
D. Carbon
B. Silver
What is the other term for American
Wire Gauge?
A. JIS
B. Brown & Sharpe
C. DIN
D. VDE
B. Brown & Sharpe
The Ampere – Hour capacity of a
battery depends on ___ of the plates.
A. Area
B. Strength
C. Thickness
D. Distance
D. Distance
A 120-volt dc motor has 100A rated
current. The allowable voltage drop
is 3% of the input voltage. What is
the maximum distance from the
supply if the wire has a diameter of
316 mils and resistivity of wire is
10.4 ohm-cmf?
A. 508 ft
B. 316 ft
C. 178 ft
D. 203 ft
C. 178 ft
A one-meter rod of 2 cm diameter is
drawn until its resistance is 100
times the initial resistance, its length
afterward is ___.
A. 8 m
B. 100 m
C. 12.5 m
D. 10 m
D. 10 m
What is the area in circular mils
(CM) of a conductor whose
diameter is 0.25 inch?
A. 65,000
B. 62,500
C. 70,000
D. 67,500
B. 62,500
A wire has a resistance of 1Ω. If the
length is increased four times and
the area is doubled the original, find
the new resistance of the wire.
A. 2 Ω
B. 4 Ω
C. 3 Ω
D. 5 Ω
A. 2 Ω
An aluminum wire has a diameter of
2 mm. What must be the diameter of
copper wire of the same resistance
and length as aluminum?
A. 1.33 mm
B. 1.56 mm
C. 1.45 mm
D. 1.75 mm
B. 1.56 mm
A copper bar has a length of 20 ft,
width of 4 inches and thickness of
0.5 inch. If the resistivity of copper
is 10.37 ohm – cmf, what is the
resistance of the bar?
A. 81.4 µΩ
B. 814 µΩ
C. 8.14 µΩ
D. 0.814 µΩ
A. 81.4 µΩ
A copper wire is drawn down such
that its length is doubled but the
volume remains the same, what is
the new resistance of the wire?
A. R/4
B. 2R
C. R/2
D. 4R
D. 4R
The resistance of a copper wire at
30°C is 50 ohms. If the temperature
coefficient of copper at 0°C is
0.00427 per °C, what is the
resistance at 100°C?
A. 63.24 ohms
B. 58.2 ohms
C. 24.5 ohms
D. 72.26 ohms
A. 63.24 ohms
A copper wire whose resistivity is
0.0043/℃ at 0℃ has its resistance
increased by 25% of its initial value
at 20℃. What is the operating
temperature?
A. 56.8℃
B. 52.5℃
C. 83.1℃
C. 83.1℃
A 120V DC motor draws a current
of 100A and is located 1000ft from
the supply. If the diameter of the
copper transmission line is 0.45 in,
what must be the voltage supply?
A. 128.32V
B. 137.05V
C. 129.82V
D. 130.24V
D. 130.24V
An electric water heater has a rating
of 1kW, 230V. The coil used as the
heating element is 10 m long and
has a resistivity of 1.724x10^-6 ohm
– cm. Determine the required
diameter of the wire in mils.
A. 2.52 mils
B. 2.43 mils
C. 3.21 mils
D. 1.36 mils
A. 2.52 mils
A hot resistance of an incandescent
lamp is 10 ohms and the rated
voltage is 50V. Find the series
resistance required to operate the
lamp from an 80V supply.
A. 8 ohms
B. 4 ohms
C. 6 ohms
D. 10 ohms
C. 6 ohms
What is the total resistance of eleven
33 kΩ resistors connected in
parallel?
A. 33 kΩ
B. 3 kΩ
C. 333 kΩ
D. 11 kΩ
B. 3kΩ
Two Resistors R1 and R2 are
connected in parallel. R1 is twice of
R2. If the current in R1, is I, what is
the current in R2?
A. I/2
Find the total resistance if 3Ω is
connected in series with the parallel
combination of 4Ω,5Ω and 20Ω
B. 5Ω
According to superposition theorem,
in a network of linear resistances
containing more than one generator
(or source of emf),
(a) the current flow at any point is
the sum of all the currents which
would flow at that point if each
generator were considered
separately, and
(b) all the other generators replaced
for the time being by resistances
equal to their voltage drops.
A. Only statement a is true.
B. Only statement b is true.
C. Both statements a and b are
true.
D. Both statements a and b are
false.
A. Only statement a is true
It is a property of matter that results
from the presence or movement of
electric charge.
A. Conductivity
B. Electricity
C. Admittance
D. Electromagnetism
B. Electricity
These are materials that allow the
essentially free passage of current
when connected to a battery or other
source of electrical energy.
A. conductors
B. Insulators
C. semiconductors
D. resistors
A. conductors
These are materials that possess low
conductivity or offer a relatively
high resistance to the flow of
electric current.
A. Conductors
B. Insulators
C. Semiconductors
D. Resistors
B. Insulators
These are materials that have
conductivity about midway between
good conductors and good
insulators.
A. conductors
B. insulators
C. semiconductors
D. resistors
C. semiconductors
It is the driving force behind current
flow.
A. voltage
B. current
C. resistance
D. mmf
A. voltage
It is the motion or transfer of
charges from one region of a
conductor to another.
A. voltage
B. emf
C. current
D. mmf
C. current
It is the difference in electric
potentials of two charged bodies.
A. voltage
B. current
C. potential difference
D. magnetomotive force
C. potential difference
Delta to wye or wye to delta
transformation technique is applied
to a ______ network.
A. one-terminal
B. two-terminal
C. three-terminal
D. complex
C. three-terminal
A load of 10 Ω was connected to a
12-V battery. The current drawn was
1.18 A. What is the internal
resistance of the battery?
A. 0.35 Ω C. 0.20 Ω
B. 0.25 Ω D. 0.30 Ω
C. 0.20 Ω
Which of the following safety rules
should be observed while working on
live electric circuit?
A. Keep yourself well insulated from
earth ground.
B. When making measurements in a
live circuit place one hand behind
your back or in your pocket.
C. Make resistance measurements
only in a live circuit.
D. Both A and B.
D. Both A and B
“The sum of the emf’s and potential
differences around a closed loop
equals zero” is a consequence of:
A. Newton’s third law
B. Newton’s second law
C. Conservation of energy
D. Conservation of charge
C. Conservation of energy
A Barangay power station supplies
60 kW to a load over 2,500 ft, 100
mm2
, two-conductors copper feeder,
the resistance of which is 0.078 ohm
per 1000 ft. The bus bar voltage is
maintained constant at 600 V.
Determine the load current.
A. 105 A C. 108 A
B. 110 A D. 102 A
C. 108 A
A circuit of three resistors rated: 10
ohms, 15 ohms and 20 ohms are
connected in delta. What would be
the resistances of the equivalent wye
connected load?
A. 0.30, 0.23 and 0.15 ohm
B. 3.0, 4.0 and 5.0 ohms
C. 3.33, 4.44 and 6.66 ohms
D. 5.77, 8.66 and 11.55 ohms
C. 3.33, 4.44 and 6.66 ohms
The hot resistance of an incandescent
lamp is about _____ times its cold
resistance.
A. 10 C. 5
B. 50 D. 100
A. 10
A certain factory takes 250 A at 220
V. It is supplied through a pair of
feeders 73.2 meters long and 1.29
cm2
in cross section. What voltage
must be maintained at the supply end
of the feeders? (Use = 1.78 -cm)
A. 111.5 V C. 333.5 V
B. 222.5 V D. 444.5 V
B. 222.5 V
Four cubic meters of water is to be
heated by means of four 1.5 kW,
230-V immersion heating elements.
Assuming the efficiency of the heater
as 90%, determine the time required
boiling the water if the initial
temperature is 20oC and if all four
elements are connected in parallel.
A. 71 hrs C. 63 hrs
B. 69 hrs D. 66 hrs
B. 69 hrs
The equivalent wye element of 3
equal resistors each equal to R and
connected in delta is
A. R C. 3/2 R
B. R/3 D. 3R
B. R/3
A coil of aluminum wire has a
resistance of 50 when its
temperature is 0°C. Determine its
resistance at 100°C if the temperature
coefficient of resistance of aluminum
at 0°C is 0.0038/°C.
A. 69 Ω C. 96 Ω
B. 65 Ω D. 90 Ω
A. 69 Ω
What is the significance of
connecting loads in parallel?
A. It makes power consumption less
B. It provides greater efficiency
C. It increases the safety factor
D. It allows independent operations
of loads
14. A wire with a smaller cross-sectional
area will produce
D. It allows independent
operations of loads
- Halving the cross-sectional area of a
conductor will:
A. Not affect the resistance.
B. Quarter the resistance.
C. Half the resistance.
D. Double the resistance.
D. Double the resistance.
An aluminum wire has a resistance of
50 at 20°C. The wire is heated to a
temperature of 100°C. Determine the
resistance of the wire at 100°C,
assuming that the temperature
coefficient of resistance at 0°C is
0.004/°C
A. 64.81 Ω C. 68.14 Ω
B. 61.84 Ω D. 63.16 Ω
A. 64.81 Ω
.If the diameter of a wire is doubled,
its current carrying capacity becomes
A. one-fourth
B. half
C. twice
D. four times
D. four times
Suppose you double the voltage in a
simple dc circuit, and cut the
resistance in half. The current will
become:
A. Four times as great
B. Twice as great
C. The same as it was before
D. Half as great
A. Four times as great
In a series circuit, the current, I, is
A. different in each resistor.
B. the same everywhere.
C. the highest near the positive and
negative terminals of the voltage
source.
D. different at all, the largest
resistance has
. B. the same everywhere
When a material becomes a
superconductor, its resistivity
becomes
A. very small
B. zero
C. about 10% of normal value
D. about 20% of normal value
B. zero
Two (2) 115-V incandescent lamps A
and B are connected in series across a
230-V source. If lamp A is rated 75
watts and lamp B is rated 50 watts,
determine the current drawn by the
series connection.
A. 0.52 A C. 0.64 A
B. 0.48 A D. 0.57 A
A. 0.52 A
. A network contains linear resistors
and ideal voltage sources. If values of
all the resistors are doubled, then the
voltage across each resistor is
A. increase by 4 times
B. half
C doubled
D. no change
D. no change
Which of the following is neither a
basic physical law nor derivable from
one?
A. Ohm’s law
B. Coulomb’s law
C. Kirchhoff’s first law
D. Kirchhoff’s second law
. A. Ohm’s law
A process equipment contains 100
gallons of water at 25oC. It is
required to bring it to boiling in 10
minutes. The heat loss is estimated to
be 5%. What is the kW rating of the
heater?
A. 125 kW C. 252 kW
B. 50.5 k D. 207 kW
D. 207 kW
If a resistor in a series circuit
becomes open, how much is the
voltage across each of the remaining
resistors that are still good?
A. Each good resistor has the full
value of applied voltage.
B. The applied voltage is split
evenly among the good resistors.
C. 0 V.
D. It cannot be determined.
C. 0 V.
A series circuit in which desired
portions of the source voltage may be
tapped off for use in equipment.
A. Voltage selector
B. Dividing network
C. Voltage trap
D. Voltage divider
D. Voltage divider
If a complex circuit is reduced to an
equivalent circuit consisting of a
single voltage source in series with a
single resistor, this is an example of:
A. Norton’s theorem
B. Thevenin’s theorem
C. Ohm’s law
D. Kirchhoff’s law
B. Thevenin’s theorem
Two resistances of 10 and 15 ohms,
each respectively are connected in
parallel. The two are then connected
in series with a 5-ohm resistance. It is
then connected across a 12-V battery,
what are the current and power?
A. 1.2 A, 17.28 W
B. 0.96 A, 11.52 W
C. 1.09 A, 13.1 W
D. 1.5 A, 20.25 W
C. 1.09 A, 13.1 W
Twelve 1 Ω resistance are used as
edges to form a cube. What is the
resistance between two diagonally
opposite corners of the cube?
A. 5/6 Ω C. 1 Ω
B. 6/5 Ω D. 3/2 Ω
A. 5/6 Ω
The polarity of a resistor’s voltage
drop is determined by
A. the direction of current through
the resistor.
B. how large the resistance is.
C. how close the resistor is to the
voltage source.
D. how far away the resistor is from
the voltage source
A. the direction of current through
the resistor.
The electric energy required to raise
the temperature of a given amount of
water is 1000 kWh. If heat losses are
25%, the total heating energy
required is _____ kWh.
A. 1500 C. 1250
B. 1333 D. 1000
B. 1333
. The resistance of a 5 m length of
wire is 600 . Determine the
resistance of an 8 m length of the
same wire.
A. 960 Ω C. 690 Ω
B. 906 Ω D. 609 Ω
C. Provides more powe
What is expected when two 20 k, 1
watt resistor in parallel are used
instead of one 10 k, 1 watt?
A. Provides higher current
B. Provides less power
C. Provides more power
D. Provides wider tolerance
C. Provides more power
Twelve identical wires of resistance 6
ohms each are arranged to form the
edge of a cube. A current of 40 mA is
led into the cube at one corner and
out at the other diagonally opposite
corner. Calculate the potential
difference developed between these
corners.
A. 0.20 V C. 0.28 V
B. 0.22 V D. 0.24 V
A. 0.20 V
The superposition theorem is used
when the circuit contains
A. reactive elements
B. active elements
C. number of voltage sources
D. single voltage source
C. number of voltage sources
.If a resistance element is part of two
loops, how many voltage drops must
be calculated for that component?
A. Two C. One
B. None D. Three
A. Two
In a normally operating parallel
circuit, the individual branch currents
are
A. independent of each other.
B. not affected by the value of the
applied voltage.
C. larger than the total current, IT.
D. None of the above.
A. independent of each other
. What is a closed path made of
several branches of the network
called?
A. Junction C. Node
B. Terminal D. Loop
. D. Loop
What is expected when two 20 k, 1
watt resistor in parallel are used
instead of one 10k, 1 watt?
A. Provides higher current
B. Provides less power
C. Provides more power
D. Provides wider tolerance
C. Provides more power
A 5-ohm resistance is connected in
parallel with a 10-ohm resistance.
Another set, a 6-ohm and 8-ohm
resistances are also connected in
parallel. The two sets are connected
in series. What is the equivalent
resistance?
A. 6.76 ohms C. 9.25 ohms
B. 14.4 ohms D. 21.2 ohms
A. 6.76 ohms
.In a parallel circuit, the individual
branch currents are
A. not related to the branch
resistance values
B. directly proportional to the branch
resistance values
C. inversely proportional to the
branch resistance values.
D. None of the above
C. inversely proportional to the
branch resistance values.
In any network made up of linear
resistances and containing more than
one source of e.m.f., the resultant
current flowing in any branch is the
algebraic sum of the currents that
would flow in that branch if each
source was considered separately.
What is this theorem?
A. Thevenin’s theorem
B. Norton’s theorem
C. Superposition theorem
D. Millman’s theorem
. C. Superposition theorem
Two resistors of 4 ohms and 6 ohms
are connected in parallel. If the total
current is 30 amperes, find the
current through each.
A. 17 A and 13 A
B. 18 A and 12A
C. 20 A and 30 A
D. 16 A and 14 A
B. 18 A and 12A
If an emf in circuit A produces a
current in circuit B, then the same
emf in circuit B produces the same
current in circuit A. This theorem is
known as
A. Maximum power transfer
theorem
B. Millman’s theorem
C. Reciprocity theorem
D. Norton’s theorem
C. Reciprocity theorem
. A 100- resistor, R1, and a 300-
resistor, R2, are in parallel across a
dc voltage source. Which resistor
dissipates more power?
A. The 300- resistor.
B. Both resistors dissipate the same
amount of power.
C. The 100- resistor.
D. It cannot be determined.
C. Reciprocity theorem
The power transferred from a supply
source to a load is at its maximum
when the resistance of the load is
_______ the internal resistance of the
source.
A. lower than
B. greater than
C. equal to
D. one-half of the
C. equal to
What If you have a 12-strand
conductor and each strand has a
radius (one-half the diameter) of 2/10
inch, what is the square mil area of
the conductor?
A. 1507965 sq. mil
B. 1705965 sq. mil
C. 1607955 sq. mil
D. 1907565 sq. mil
A. 1507965 sq. mil
A 5- and 10- resistor are
connected in series across a dc
voltage source. Which resistor will
dissipate more power?
A. the 5- resistor.
B. the 10- resistor.
C. It depends on how much the
current is.
D. They will both dissipate the same
amount or power.
B. the 10- resistor.
The first step in Thevenin’s theorem
is to:
A. determine the short-circuit current
B. open the load under test
C. short the load under test
D. determine the open-circuit current
B. open the load under test
