WorksheetsDC Circuits Quiz
Total questions: 122
Worksheet time: 1hrs 4mins
If a resistance to which a constant voltage is applied is halved, what power dissipation will result?
Doubled
Halved
Stays the same
Quadrupled
If the reference point is changed to the earth point then any voltage taken w.r.t. the earth is known as
Absolute potential
Earth ground
Relative voltage
Absolute point
What is the significance of connecting loads in parallel?
It makes power consumption less
It provides greater efficiency
It increases the safety factor
It allows independent operations of loads
Which of the following safety rules should be observed while working on live electric circuit?
Keep yourself well insulated from earth ground.
When making measurements in a live circuit place one hand behind your back or in your pocket.
Make resistance measurements only in a live circuit.
Both A and B.
Under the maximum power transfer condition, what is the power absorbed by the load resistance R_L?
526 W
562 W
625 W
652 W
The hot resistance of an incandescent lamp is about _____ times its cold resistance.
10
50
5
100
If a resistor in a series circuit is shorted, the series current, I,
decreases
stays the same.
increases.
drops to zero.
The equivalent wye element of 3 equal resistors each equal to R and connected in delta is
R
R/3
3/2 R
3R
A coil of aluminum wire has a resistance of 50 Ω 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.
69 Ω
65 Ω
96 Ω
90 Ω
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 ρ = 1.78 μΩ-cm)
111.5 V
222.5 V
333.5 V
444.5 V
A wire with a smaller cross-sectional area will produce:
less heat
more conductance
less resistance
more heat
Halving the cross-sectional area of a conductor will:
Not affect the resistance.
Quarter the resistance.
Half the resistance.
Double the resistance.
An aluminum wire has a resistance of 50 Ω 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
64.81 Ω
61.84 Ω
68.14 Ω
63.16 Ω
In Norton’s Theorem, the short circuit current is obtained by
opening the load terminals
shorting the load terminals
opening the voltage source
shorting the voltage source
Delta to wye or wye to delta transformation technique is applied to a ______ network.
one-terminal
two-terminal
three-terminal
complex
If the diameter of a wire is doubled, its current carrying capacity becomes
one-fourth
half
twice
four times
If a resistance element is part of two loops, how many voltage drops must be calculated for that component?
Two
None
One
Three
Find the equivalent resistance of the figure shown below:
10 ohms
20 ohms
15 ohms
5 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
Twice as great
The same as it was before
Half as great
In a series circuit, the current, I, is
different in each resistor.
the same everywhere.
the highest near the positive and negative terminals of the voltage source.
different at all, the largest resistance has
When a material becomes a superconductor, its resistivity becomes
very small
zero
about 10% of normal value
about 20% of normal value
“The sum of the emf’s and potential differences around a closed loop equals zero” is a consequence of:
Newton’s third law
Newton’s second law
Conservation of energy
Conservation of charge
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.
0.52 A
0.48 A
0.64 A
0.57 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
increase by 4 times
half
doubled
no change
Which of the following is neither a basic physical law nor derivable from one?
Ohm’s law
Coulomb’s law
Kirchhoff’s first law
Kirchhoff’s second law
Which of the following is the poorest conductor of electricity?
Aluminum
Nichrome
Copper
All of the above
If a resistor in a series circuit becomes open, how much is the voltage across each of the remaining resistors that are still good?
Each good resistor has the full value of applied voltage.
The applied voltage is split evenly among the good resistors.
0 V.
It cannot be determined.
A series circuit in which desired portions of the source voltage may be tapped off for use in equipment.
Voltage selector
Dividing network
Voltage trap
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:
Norton's theorem
Thevenin's theorem
Ohm's law
Kirchhoff's law
If one branch of a parallel circuit is short-circuited.
the fuse in the main line will blow.
the voltage across the short-circuited branch will measure the full value of applied voltage.
all the remaining branches are effectively short-circuited as well.
Both A and C.
Twelve 1 Ω resistance are used as edges to form a cube. What is the resistance between two diagonally opposite corners of the cube?
5/6 Ω
6/5 Ω
1 Ω
3/2 Ω
The polarity of a resistor’s voltage drop is determined by
the direction of current through the resistor.
how large the resistance is.
how close the resistor is to the voltage source.
how far away the resistor is from the voltage source
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.
1500
1333
1250
1000
The resistance of a 5 m length of wire is 600 Ω. Determine the resistance of an 8 m length of the same wire.
960 Ω
906 Ω
690 Ω
609 Ω
What is expected when two 20 kΩ, 1 watt resistor in parallel are used instead of one 10 kΩ, 1 watt?
Provides higher current
Provides less power
Provides more power
Provides wider tolerance
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.
0.20 V
0.22 V
0.24 V
0.28 V
The superposition theorem is used when the circuit contains
reactive elements
active elements
number of voltage sources
single voltage source
In a normally operating parallel circuit, the individual branch currents are
independent of each other.
not affected by the value of the applied voltage.
larger than the total current, IT.
None of the above.
What is a closed path made of several branches of the network called?
Junction
Node
Terminal
Loop
If one branch of a parallel circuit becomes open,
all remaining branch currents increase.
the voltage across the open branch will be 0 V.
the remaining branch currents do not change in value.
the equivalent resistance of the circuit decreases.
In a parallel circuit, the individual branch currents are
not related to the branch resistance values
directly proportional to the branch resistance values
inversely proportional to the branch resistance values.
None of the above
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?
Thevenin's theorem
Norton's theorem
Superposition theorem
Millman's 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.
17 A and 13 A
18 A and 12A
20 A and 30 A
16 A and 14 A
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
Maximum power transfer theorem
Millman’s theorem
Reciprocity theorem
Norton’s theorem
A 100-Ω resistor, R1, and a 300-Ω resistor, R2, are in parallel across a dc voltage source. Which resistor dissipates more power?
The 300-Ω resistor.
Both resistors dissipate the same amount of power.
The 100-Ω resistor.
It cannot be determined.
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.
lower than
greater than
equal to
one-half of the
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?
1507965 sq. mil
1705965 sq. mil
1607955 sq. mil
1907565 sq. mil
A 5-Ω and 10-Ω resistor are connected in series across a dc voltage source. Which resistor will dissipate more power?
the 5-Ω resistor.
the 10-Ω resistor.
It depends on how much the current is.
They will both dissipate the same amount or power.
The first step in Thevenin's theorem is to:
determine the short-circuit current
open the load under test
short the load under test
determine the open-circuit current
In a parallel ac circuit with XL and XC,
IL and Ic are 90° out of phase.
IL and IC are in phase.
IL and IC are 180° out of phase.
XL and XC are 90° out of phase.
What is the term for the out-of-phase power associated with inductors and capacitors?
Effective power.
True power.
Peak envelope power.
Reactive power.
In an AC circuit, if the voltage and current are in phase, the circuit is
resistive
capacitive
reactive
inductive
For a capacitor in a sine-wave ac circuit,
Vc lags ic by 90°
ic leads Vc by 90°
ic and Vc have the same frequency.
All of the above.
Calculate the r.m.s. value of a sinusoidal current of maximum value 20A.
7.07 A
14.14 A
28.28 A
26.25 A
An alternating voltage is given by v=75 sin (200πt −0.25) volts. Find the phase angle (in degrees and minutes)
14.32 (lagging)
14.32 (leading)
31.83 (lagging)
31.83 (leading)
In a parallel RL circuit,
IL lags IR by 90°.
IL leads IR by 90°.
IL and IR are in phase.
IR lags IL by 90°.
Calculate the current taken by a 10 μF capacitor when connected to a 200 V, 100 Hz supply.
0.1257 A
12.57 A
125.7 A
1.257 A
What is the power factor (PF) of a purely resistive ac circuit?
0.
1.
0.707.
Without values, it cannot be determined.
A resistive and a capacitive load of equal magnitude is connected in series, determine the phase difference between the voltage and the current.
current leads the voltage by 45°
current lags the voltage by 45°
current leads the voltage by 90°
current lags the voltage by 90°
For an inductor in a sine-wave ac circuit,
VL leads iL by 90°.
VL lags iL by 90°.
VL and iL are in phase.
None of the above.
What will happen when the power factor of a circuit is increased?
Reactive power increases
Active power increases
Both active and reactive powers increases
Both active and reactive powers decreases
Calculate the capacitive reactance of a capacitor of 20 μF when connected to an a.c. circuit of frequency 20 Hz
397.9 ohms
379
Calculate the capacitive reactance of a capacitor of 20 μF when connected to an a.c. circuit of frequency 20 Hz
397.9 ohms
379.8 ohms
399.7 ohms
378.9 ohms
The impedance in the study of electronics is represented by resistance and ________.
inductance and capacitance
inductance
reactance
capacitance
In a series RLC circuit,
X_L and X_C are 180 out of phase.
I_L and I_C are 180 out of phase.
I_L and X_C are 180 out of phase.
I_L and X_C are in phase.
A resistive and a capacitive load of equal magnitude is connected in series, determine the phase difference between the voltage and the current.
current leads the voltage by 45°
current lags the voltage by 45°
current leads the voltage by 90°
current lags the voltage by 90°
In a series RC circuit,
V_c leads V_R by 90°
V_c and I are in phase.
V_c lags V_r by 90°
Both B and C.
An e.m.f. of 200 V at a frequency of 2 kHz is applied to a coil of pure inductance 50 mH. Determine the reactance of the coil and the current flowing in the coil.
628 Ω; 0.318 A
628 Ω; 0.328 A
630 Ω; 0.318 A
618 Ω; 0.318 A
If a circuit has an admittance of Y = 0.2 + j0.6, the circuit is
purely inductive
inductive
capacitive
reactive
What is the significance of connecting loads in parallel?
It makes power consumption less
It provides greater efficiency
It increases the safety factor
It allows independent operations of loads
What is the term used to identify an AC voltage that would cause the same heating in a resistor as a corresponding value of DC voltage?
Cosine voltage.
Power factor.
Root mean square (RMS).
Average voltage.
When the frequency of the applied voltage increases in a series RC circuit,
the phase angle, θ, becomes more negative.
Z_T increases.
Z_T decreases.
Both A and C.
The voltages across three components in a series circuit when connected across an a.c. supply are: 1 v30 sin 300 t 6 π = π− volts, 2 v40 sin 300 t 4 π = π+ volts and 3 v50 sin 300 t 3 π = π+ volts. Calculate the supply voltage in sinusoidal form.
(S V97.39sin300t0.620V=π+)
(S V97.93sin300t0.620V=π+)
(S V79.39sin300t0.620V=π+)
(S V97.39sin300t0.602V=π+)
The product of the readings of an AC voltmeter and AC ammeter is called:
Apparent power.
True power.
Power factor.
Current power.
A resistor of 150 Ω, a coil with reactance 100 Ω and a capacitor with reactance - 200 Ω are connected in series. What is the complex impedance R + jX?
150 + j100
150 – j200
100 – j200
150 – j100
In an ac circuit with only series capacitors,
V_T leads I_T by 90°.
V_T lags I_T by 90°.
each capacitor voltage drop leads I_T by 90°.
Both A and C.
A value of –j500Ω represents
500 Ω of inductive reactance.
500 Ω of capacitive reactance.
500 Ω of resistance.
500 Ω of conductance.
Inductive reactance, X_L,
applies only to non-sinusoidal waveforms or dc.
applies only to sine waves.
applies to either sinusoidal or non-sinusoidal waveforms.
is inversely proportional to frequency.
Susceptance, B, is the
reciprocal of impedance.
reciprocal of reactance.
reciprocal of resistance.
same as conductance.
What is the total impedance of a series AC circuit having a resistance of 6 ohms, an inductive reactance of 17 ohms, and zero capacitive reactance?
6.6 Ω
18 Ω
11 Ω
23 Ω
When the frequency of the applied voltage decreases in a parallel RL circuit,
the phase angle, θ_1, becomes less negative.
Z_EQ increases.
Z_EQ decreases.
Both A and B.
An impedance draws a current i = 10 cos (ωt – 30°) from a voltage, v = 220 sin (ωt + 30°). What is the impedance?
15.6 – j15.6
15.6 + j15.6
19.1 – j11.1
11.1 + j19.1
In a parallel RC circuit,
I_c lags I_R by 90°
I_R and I_C are in phase.
I_C leads I_R by 90°.
I_R leads I_C by 90°.
If a circuit has an admittance of Y = 0.5- j0.9, the circuit is
resistive
capacitive
inductive
reactive
A coil, resistor and capacitor are in parallel. The resistance is 1 Ω; the capacitive susceptance is 1.0 siemens; the inductive susceptance is - 1.0 siemens. Then the frequency is cut to half its former value. What will be the admittance vector, G + jB, at the new frequency?
1 + j0
1 + j1.5
1 – j1.5
1 – j2
A branch current of +j250 mA represents
250 mA of inductive current.
250 mA of resistive current.
250 mA of capacitive current.
250 mA of in-phase current.
A capacitor has a capacitive reactance of 400 Ω when connected to a 100 V, 25 Hz supply. Determine its capacitance and the current taken from the supply.
15.92 μF; 0.25 A
15.92 μF; 0.15 A
15.29 μF; 0.25 A
15.92 μF; 0.025 A
What happens to reactive power in a circuit that has both inductors and capacitors?
It is dissipated as heat in the circuit.
It alternates between magnetic and electric fields and is not dissipated.
It is dissipated as inductive and capacitive fields.
It is dissipated as kinetic energy within the circuit.
How do you compute true power (power dissipated in the circuit) in a circuit where AC voltage and current are out of phase?
Multiply RMS voltage times RMS current.
Subtract apparent power from the power factor.
Divide apparent power by the power factor.
Multiply apparent power times the power factor.
In a parallel RC circuit,
V_A and I_R are in phase.
V_A and I_C are in phase.
I_C and I_R are in phase.
V_A and I_R are 90° out of phase.
An alternating voltage given by v = 100 sin 240t volts is applied across a coil of resistance 32 Ω and inductance 100 mH. Determine the circuit impedance.
40 ohms
50 ohms
20 ohms
30 ohms
What is a sine wave?
A constant-voltage, varying-current wave.
A wave whose amplitude at any given instant can be represented by the projection of a point on a wheel rotating at a uniform speed.
A wave following the laws of the trigonometric tangent function.
A wave whose polarity changes in a random manner.
A 120 mH inductor has a 50 mA, 1 kHz alternating current flowing through it. Find the p.d. across the inductor
36.7 V
33.7 V
35.7 V
37.7 V
What type of wave is characterized by a rise time significantly faster than the fall time (or vice versa)?
Cosine wave.
Square wave.
Sawtooth wave.
Sine wave.
What type of wave is made up of sine waves of the fundamental frequency and all the odd harmonics?
Square.
Cosine.
Sine.
Tangent.
When the frequency of the applied voltage increases in a parallel RC circuit,
the phase angel, , increases.
Z EQ increases.
Z EQ decreases.
Both A and C.
How many degrees are there in one complete sine wave cycle?
90 degrees.
270 degrees.
180 degrees.
360 degrees.
In a series RC circuit,
V c and V R are in phase.
V T and I are always in phase.
V R and I are in phase.
V R leads I by 90.
What is the description of a square wave?
A wave with only 300 degrees in one cycle.
A wave whose periodic function is always negative.
A wave whose periodic function is always positive.
A wave that abruptly changes back and forth that abruptly changes back and forth between two voltage levels and stays at these levels for equal amounts of time.
What type of wave is made up of sine waves at the fundamental frequency and all the harmonics?
Sawtooth wave.
Square wave.
Sine wave.
Cosine wave.
Magnetic flux can always be attributed to:
Ferromagnetic materials
Aligned atoms
Motion of charged particles *
The geomagnetic field
A straight conductor 500 mm long is moved with constant velocity at right angles both to its length and to a uniform magnetic field. Given that the e.m.f. induced in the conductor is 2.5 V and the velocity is 5 m/s, calculate the flux density of the magnetic field. If the conductor forms part of a closed circuit of total resistance 5 ohms, calculate the force on the conductor.
0.25 N *
0.025 N
2.5 N
250 N
Which of the following statements is true?
Unlike charges repel each other.
Like charges repel each other.
Unlike charges attract each other.
Both B and C.
A changing magnetic field:
Produces an electric current in an insulator.
Magnetizes the earth.
Produces a fluctuating electric field. *
Results from a steady electric current.
A conductor of length 15 cm is moved at 750 mm/s at right-angles to a uniform flux density of 1.2 T. Determine the e.m.f. induced in the conductor.
0.135 V *
0.0135 V
1.350 V
13.50 V
For the current carrying conductor lying in the magnetic field shown in the figure below, the direction of the force on the conductor is:
downwards *
upwards
to the right
to the left
Which is the wrong statement? The magnetizing force at the center of a circular coil varies
directly as the number of its turns*
directly as the current
directly as its radius
inversely as its radius
A 25 cm long conductor moves at a uniform speed of 8 m/s through a uniform magnetic field of flux density 1.2 T. Determine the current flowing in the conductor when its ends are connected to a load of 15 ohms resistance.
1.6 A
0.16 A *
16 A
0.016 A
Two bar magnets are placed parallel to each other and about 2 cm apart, such that the south pole of one magnet is adjacent to the north pole of the other. With this arrangement, the magnets will:
attract each other *
have no effect on each other
repel each other
lose their magnet ism
A car is travelling at 80 km/h. Assuming the back axle of the car is 1.76 m in length and the vertical component of the earth’s magnetic field is 40 T, find the e.m.f. generated in the axle due to motion.
1.56 mV
15.6 mV
0.156 mV
156 mV
Calculate the current required in a 240 mm length of conductor of a d.c. motor when the conductor is situated at right-angles to the magnetic field of flux density 1.25 T, if a force of 1.20 N is to be exerted on the conductor.
4 A *
6 A
2 A
5 A
If a neutral atom loses one of its valence electrons, it becomes a (n)
negative ion.
electrically charged atom.
positive ion.
Both B and C. *
For the current-carrying conductor lying in the magnetic field shown in the figure below, the direction of the current in the conductor is:
towards the viewer
away from the viewer
upwards
downwards
A conductor 300 mm long carries a current of 13 A and is at right-angles to a magnetic field between two circular pole faces, each of diameter 80 mm. If the total flux between the pole faces is 0.75 mWb, calculate the force exerted on the conductor.
0.0582 N
5.82 N
0.582 N *
58.2 N
Calculate the force exerted on a charge of 2x10-18 C travelling at 2x10 6 m/s perpendicular to a field of density 2x10-7 T.
8.0 x 10-19 N *
0.8 x 10-19 N
0.008 x 10-19 N
80.0 x 10-19 N
The most basic particle of negative charge is the ____.
coulomb
proton
electron *
neutron
Which of the following statements is true?
Unlike charges repel each other.
Like charges repel each other.
Unlike charges attract each other.
Both B and C. *
Aluminum, with an atomic number of 13, has
13 valence electrons.
3 valence electrons.
13 protons in its nucleus.
Both B and C. *
The nucleus of an atom is made up of
electrons and neutrons.
ions.
neutrons and protons.
electrons only.
One ampere of current corresponds to
1 C/1 s *
1 J/1 C
6.25 X 10 18 electrons
0.16 x 10-18 C/s
Conventional current is considered
the motion of negative charges in the opposition direction of electron flow.
the motion of positive charges in the same direction as electron flow.
the motion of positive charges in the opposition direction of electron flow.
None of the above.
The coulomb is a unit of
