1.
A resistor is connected across a 50 V source. What is the current in the resistor if the color code is red, orange, orange, silver?
Correct Answer
B. 2.2 mA
Explanation
The color code for the resistor indicates its resistance value. In this case, red represents 2, orange represents 3, and silver represents a decimal multiplier of 0.01. Therefore, the resistance of the resistor is 23 * 0.01 = 0.23 ohms. Using Ohm's Law (V = IR), we can calculate the current by dividing the voltage (50 V) by the resistance (0.23 ohms). The current is approximately 217.39 mA, which is closest to 2.2 mA.
2.
How much voltage is needed to produce 2.5 A of current through a 200 resistor?
Correct Answer
B. 500 V
Explanation
To calculate the voltage needed, we can use Ohm's Law which states that voltage (V) is equal to current (I) multiplied by resistance (R). In this case, the current is given as 2.5 A and the resistance is 200 Ω. Plugging these values into the formula, we get V = 2.5 A * 200 Ω = 500 V. Therefore, the correct answer is 500 V.
3.
Twelve volts are applied across a resistor. A current of 3 mA is measured. What is the value of the resistor?
Correct Answer
C. 4 k
Explanation
The value of the resistor is 4 k. This can be determined using Ohm's Law, which states that the current flowing through a resistor is equal to the voltage across it divided by its resistance. In this case, the voltage is 12 volts and the current is 3 mA (or 0.003 A). By rearranging the formula, we can solve for the resistance: R = V/I = 12/0.003 = 4000 ohms, which is equivalent to 4 k.
4.
When a fourth resistor is connected in series with three resistors, the total resistance
Correct Answer
B. Increases
Explanation
When a fourth resistor is connected in series with three resistors, the total resistance increases. This is because when resistors are connected in series, their resistances add up. Adding a fourth resistor increases the total resistance even more, resulting in an overall increase in the total resistance.
5.
The total power in a certain circuit is 12 W. Each of the four equal-value series resistors making up the circuit dissipates
Correct Answer
C. 3 W
Explanation
The answer is 3 W because the total power in the circuit is given as 12 W and there are four equal-value series resistors. Since the resistors are in series, the total power is divided equally among them. Therefore, each resistor dissipates 12 W / 4 = 3 W.
6.
Three 680 resistors are connected in series with a 470 V source. Current in the circuit is
Correct Answer
B. 230 mA
Explanation
When resistors are connected in series, the total resistance is equal to the sum of individual resistances. In this case, the three 680 Ω resistors are connected in series, so the total resistance is 680 Ω + 680 Ω + 680 Ω = 2040 Ω.
According to Ohm's Law, the current flowing through a circuit is equal to the voltage divided by the resistance. In this case, the voltage is 470 V and the resistance is 2040 Ω.
Using Ohm's Law, we can calculate the current as follows:
Current = Voltage / Resistance = 470 V / 2040 Ω = 0.230 A = 230 mA.
Therefore, the correct answer is 230 mA.
7.
If a 6 V and a 9 V source are connected series aiding, the total voltage is
Correct Answer
D. 15 V
Explanation
When two voltage sources are connected in series aiding, their voltages add up. In this case, the 6 V and 9 V sources are connected in series aiding, so the total voltage is the sum of the two voltages, which is 6 V + 9 V = 15 V.
8.
A certain Wheatstone bridge has the following resistor values: R_{1} = 10 k, R_{2} = 720 , and R_{4} = 2.4 k. The unknown resistance is
Correct Answer
D. 3,000
Explanation
The unknown resistance in the Wheatstone bridge can be calculated using the formula:
R3 = (R1 * R4) / R2
Plugging in the given values, we get:
R3 = (10k * 2.4k) / 720
Simplifying the expression:
R3 = 24k / 720
R3 = 30
Therefore, the unknown resistance is 3,000.
9.
The branch current method uses
Correct Answer
A. Kirchhoff's voltage and current laws
Explanation
The branch current method uses Kirchhoff's voltage and current laws because these laws are fundamental principles in circuit analysis. Kirchhoff's voltage law states that the sum of the voltage drops around any closed loop in a circuit is equal to the sum of the voltage sources in that loop. Kirchhoff's current law states that the sum of currents entering a node is equal to the sum of currents leaving that node. These laws are essential for determining the currents flowing through different branches in a circuit using the branch current method.
10.
How many degrees are there in /3 rad?
Correct Answer
B. 60°
Explanation
One radian is equal to 180 degrees. Therefore, dividing 180 degrees by 3 gives us 60 degrees.
11.
To produce an 800 Hz sine wave, a four-pole generator must be operated at
Correct Answer
B. 400 rps
Explanation
To produce an 800 Hz sine wave, a four-pole generator must be operated at 400 rps. This is because the frequency of the output voltage of a generator is directly proportional to the rotational speed of the rotor. In a four-pole generator, each complete revolution of the rotor produces two cycles of the output voltage. Therefore, to generate a frequency of 800 Hz, the rotor must rotate at a speed of 400 revolutions per second (rps), which corresponds to 400 Hz.
12.
If the peak of a sine wave is 13 V, the peak-to-peak value is
Correct Answer
C. 26 V
Explanation
The peak-to-peak value of a sine wave is twice the peak value. Since the peak value is given as 13 V, the peak-to-peak value would be 2 times 13 V, which equals 26 V. Therefore, the correct answer is 26 V.
13.
A signal with a 400 s period has a frequency of
Correct Answer
B. 2,500 Hz
Explanation
The frequency of a signal is the number of cycles it completes in one second. To find the frequency, we can use the formula: frequency = 1/period. In this case, the period is given as 400 s. Using the formula, we can calculate the frequency as 1/400 = 0.0025 Hz. However, the options provided are in Hz, so we need to convert the frequency to Hz by multiplying it by 1000. Therefore, the correct answer is 2,500 Hz.
14.
A sawtooth wave has a period of 10 ms. Its frequency is
Correct Answer
C. 100 Hz
Explanation
The frequency of a wave is the number of complete cycles it completes in one second. Since the period of the sawtooth wave is given as 10 ms (milliseconds), we can find the frequency by taking the reciprocal of the period. 1/10 ms is equal to 100 Hz, which means the sawtooth wave completes 100 cycles in one second. Therefore, the correct answer is 100 Hz.
15.
A 2 mH, a 3.3 mH, and a 0.2 mH inductor are connected in series. The total inductance is
Correct Answer
D. 5.5 mH
Explanation
When inductors are connected in series, the total inductance is equal to the sum of the individual inductances. Therefore, in this case, the total inductance is 2 mH + 3.3 mH + 0.2 mH = 5.5 mH.
16.
An ohmmeter is connected across an inductor and the pointer indicates zero ohms. The inductor is
Correct Answer
C. Shorted
Explanation
If an ohmmeter is connected across an inductor and the pointer indicates zero ohms, it means that there is a direct connection between the terminals of the inductor, resulting in a short circuit. This indicates that the inductor is shorted.
17.
The current through a 120 mH coil is changing at a rate of 150 mA/s. The voltage induced across the coil is
Correct Answer
B. 18 mV
Explanation
The voltage induced across a coil is given by the formula V = L * di/dt, where V is the induced voltage, L is the inductance of the coil, and di/dt is the rate of change of current. In this case, the inductance is given as 120 mH and the rate of change of current is 150 mA/s. Plugging these values into the formula, we get V = 120 mH * 150 mA/s = 18 mV. Therefore, the voltage induced across the coil is 18 mV.
18.
In a three-phase system, the voltages are separated by
Correct Answer
C. 120°
Explanation
In a three-phase system, the voltages are separated by 120°. This is because a three-phase system consists of three voltages that are 120° out of phase with each other. This phase separation allows for a more efficient and balanced distribution of power in electrical systems.
19.
In a three-phase system, when the loads are perfectly balanced, the neutral current is
Correct Answer
A. Zero
Explanation
In a three-phase system, when the loads are perfectly balanced, the neutral current is zero. This is because in a balanced system, the three phases carry equal currents and have equal magnitudes but are out of phase with each other by 120 degrees. As a result, the sum of the currents in the three phases cancels out at the neutral point, resulting in zero current flowing through the neutral conductor.
20.
In a balanced three-phase load, each phase has
Correct Answer
A. An equal amount of power
Explanation
In a balanced three-phase load, each phase has an equal amount of power. This means that the power consumption is evenly distributed among the three phases. This is achieved by ensuring that the loads connected to each phase are of equal magnitude and have the same power factor. By having an equal amount of power in each phase, the load is balanced and the system operates efficiently without any phase imbalance issues.
21.
In a Y-connected circuit, between each line voltage and the nearest phase voltage, there is a phase angle of
Correct Answer
B. 30°
Explanation
In a Y-connected circuit, the phase angle between each line voltage and the nearest phase voltage is 30°. This is because in a Y-connected system, the line voltage is equal to the square root of 3 times the phase voltage. The phase angle between them is determined by the relationship between the line voltage and the phase voltage. In a Y-connected system, the line voltage leads the phase voltage by 30°.
22.
The most common type of ac motor is the
Correct Answer
C. Three-phase induction motor
Explanation
The most common type of AC motor is the three-phase induction motor. This type of motor is widely used in industrial and commercial applications due to its efficiency, reliability, and simplicity. It consists of a stator with three windings and a rotor that is made of conducting bars. The rotating magnetic field produced by the stator windings induces currents in the rotor, which in turn creates a magnetic field. The interaction between the stator and rotor magnetic fields causes the rotor to rotate, making it suitable for a wide range of applications.
23.
In Delta connected generator, all of the phase voltages are
Correct Answer
B. Equal in magnitude
Explanation
In a Delta connected generator, the phase voltages are equal in magnitude. This means that each phase of the generator produces the same voltage, ensuring balanced and consistent power output. The equal magnitude of the phase voltages allows for efficient distribution of electrical energy and ensures that the load receives a balanced supply of power.
24.
Materials with lots of free electrons are called
Correct Answer
A. Conductors
Explanation
Materials with lots of free electrons are called conductors. Conductors are substances that allow the flow of electric current through them easily due to the presence of a large number of free electrons. These free electrons are not tightly bound to their atoms and can move freely within the material. This property makes conductors good at conducting electricity and heat. Examples of conductors include metals like copper, silver, and aluminum.
25.
The unit of electrical charge is the
Correct Answer
A. Coulomb
Explanation
The unit of electrical charge is the coulomb. The coulomb is a fundamental unit of electric charge in the International System of Units (SI). It is defined as the amount of electric charge that passes through a point in a conductor in one second when a current of one ampere is flowing. The coulomb is named after the French physicist Charles-Augustin de Coulomb, who made significant contributions to the field of electromagnetism.
26.
Current flows in a circuit when
Correct Answer
B. A switch is closed
Explanation
When a switch is closed in a circuit, it completes the electrical path between the power source and the load, allowing current to flow. This is because the closed switch creates a continuous loop for the electrons to move through, enabling the flow of electric charge. On the other hand, when the switch is opened, it breaks the circuit and interrupts the flow of current. Therefore, the correct answer is that current flows in a circuit when a switch is closed.
27.
The minimum resistance value for a blue, gray, red, silver resistor is
Correct Answer
B. 6,120
Explanation
The correct answer is 6,120. This is because the color code for blue, gray, red, silver resistors corresponds to the values 6, 1, 2, and 0 respectively. By combining these values, we get 6,120 as the minimum resistance value for this type of resistor.
28.
Which of the following is not a type of energy source?
Correct Answer
B. Rheostat
Explanation
A rheostat is not a type of energy source. It is a variable resistor that is used to control the flow of electric current in a circuit. It does not generate or provide energy like a generator, solar cell, or battery. Instead, it regulates the amount of current flowing through a circuit by changing its resistance.
29.
Electrons in the outer orbit are called
Correct Answer
B. Valences
Explanation
Electrons in the outer orbit of an atom are called valence electrons. These electrons are involved in chemical bonding and determine the reactivity and properties of an element. Valence electrons are responsible for the formation of chemical bonds between atoms, allowing them to share or transfer electrons and form compounds. Understanding the number and arrangement of valence electrons is crucial in predicting the behavior and interactions of elements in chemical reactions.
30.
A thermistor is a type of
Correct Answer
B. Resistor
Explanation
A thermistor is a type of resistor. A resistor is an electrical component that restricts the flow of electric current. In the case of a thermistor, its resistance changes with temperature. This property makes it useful in applications where temperature monitoring or control is required, such as in thermostats or temperature sensors. Therefore, the correct answer is resistor.
31.
A two-terminal variable resistor is known as a
Correct Answer
C. Rheostat
Explanation
A two-terminal variable resistor is known as a rheostat. A rheostat is a type of resistor that can be adjusted to vary the amount of current flowing through a circuit. It is commonly used to control the brightness of lights or the speed of motors. Unlike a potentiometer, which has three terminals and is used to measure voltage, a rheostat only has two terminals and is used to control current. A thermistor, on the other hand, is a type of resistor that changes its resistance with temperature, and a wiper is a part of a potentiometer that makes contact with the resistive element.
32.
When the current is 2.5 A, how many coulombs pass a point in 0.2 s?
Correct Answer
C. 0.5 C
Explanation
In order to calculate the number of coulombs that pass a point in a given time, we can use the formula Q = I * t, where Q is the charge in coulombs, I is the current in amperes, and t is the time in seconds. In this case, the current is 2.5 A and the time is 0.2 s. Plugging these values into the formula, we get Q = 2.5 A * 0.2 s = 0.5 C. Therefore, 0.5 C is the correct answer.
33.
A multimeter measures
Correct Answer
D. Current, voltage, and resistance
Explanation
A multimeter is a versatile device used to measure electrical quantities. It can measure current, which is the flow of electric charge in a circuit. It can also measure voltage, which is the potential difference between two points in a circuit. Additionally, a multimeter can measure resistance, which is the opposition to the flow of electric current. Therefore, the correct answer is that a multimeter can measure current, voltage, and resistance.
34.
A circuit breaker is a
Correct Answer
C. Resettable protective device
Explanation
A circuit breaker is a resettable protective device. Unlike a fuse, which needs to be replaced once it has blown, a circuit breaker can be reset after it has tripped due to an overload or short circuit. It is designed to automatically interrupt the flow of electricity when it detects a fault, protecting the electrical circuit and preventing damage to the connected devices. By resetting the circuit breaker, the circuit can be restored to its normal functioning, making it a convenient and efficient protective device for electrical systems.
35.
An ohmmeter is an instrument for measuring
Correct Answer
C. Resistance
Explanation
An ohmmeter is an instrument specifically designed to measure resistance. It works by applying a known voltage to the component being tested and measuring the resulting current. By using Ohm's law (V=IR), the ohmmeter can calculate the resistance of the component. Therefore, the correct answer is resistance.
36.
If the cross-sectional area of a magnetic field increases, but the flux remains the same, the flux density
Correct Answer
B. Decreases
Explanation
When the cross-sectional area of a magnetic field increases but the flux remains the same, it means that the same amount of magnetic field lines are spread over a larger area. This implies that the magnetic field is less concentrated, resulting in a decrease in flux density.
37.
The unit for reluctance is
Correct Answer
B. At/Wb
Explanation
The unit for reluctance is At/Wb. Reluctance is a measure of the opposition offered by a magnetic circuit to the flow of magnetic flux. It is analogous to resistance in an electrical circuit. The unit At/Wb represents ampere-turns per weber, where ampere-turns is the measure of magnetomotive force and weber is the measure of magnetic flux. Therefore, At/Wb is the appropriate unit for reluctance.
38.
The unit for permeability is
Correct Answer
A. Wb/At × m
Explanation
The unit for permeability is Wb/At × m, which stands for Weber per Ampere times meter. Permeability is a measure of how easily a material can be magnetized, and it is represented by the symbol μ. The unit Wb/At × m represents the amount of magnetic flux (Weber) per unit current (Ampere) times the distance (meter). This unit is commonly used in physics and engineering to quantify the magnetic properties of materials.
39.
The direction of a magnetic field within a magnet is
Correct Answer
A. From south to north
Explanation
The correct answer is from south to north. In a magnet, the magnetic field lines always flow from the south pole to the north pole. This is because magnetic field lines are imaginary lines that represent the direction and strength of the magnetic field. They are conventionally drawn from the north pole to the south pole outside the magnet and from the south pole to the north pole inside the magnet.
40.
The ability of a material to remain magnetized after removal of the magnetizing force is known as
Correct Answer
D. Retentivity
Explanation
Retentivity refers to the ability of a material to retain its magnetization even after the magnetizing force is removed. It is a measure of how well a material can "remember" its magnetic properties. A material with high retentivity will retain its magnetization for a longer period of time, while a material with low retentivity will quickly lose its magnetization.
41.
An electromagnetic field exists only when there is
Correct Answer
D. Current
Explanation
An electromagnetic field exists only when there is a current. This is because an electromagnetic field is created by the flow of electric current. When current flows through a conductor, it generates a magnetic field around it. This magnetic field, in turn, creates an electromagnetic field. Without the presence of current, there is no flow of electrons to generate the magnetic field, and therefore no electromagnetic field.
42.
A 10 F, 20 F, 22 F, and 100 F capacitor are in parallel. The total capacitance is
Correct Answer
D. 152 F
Explanation
When capacitors are connected in parallel, the total capacitance is equal to the sum of the individual capacitances. Therefore, the total capacitance in this case would be 10F + 20F + 22F + 100F = 152F.
43.
What is the capacitance when Q = 60 C and V = 12 V?
Correct Answer
B. 5 F
Explanation
The capacitance of a capacitor is defined as the ratio of the charge stored on the capacitor to the voltage across it. In this case, the charge (Q) is given as 60 C and the voltage (V) is given as 12 V. By using the formula for capacitance, C = Q/V, we can calculate the capacitance as 60 C / 12 V = 5 F. Therefore, the correct answer is 5 F.
44.
Which of the following capacitors is polarized?
Correct Answer
D. Electrolytic
Explanation
Electrolytic capacitors are polarized capacitors, meaning they have a positive and negative terminal. This is because they are constructed with an electrolyte solution and a thin oxide layer, which allows them to store large amounts of charge. The polarity is important because reversing the voltage can damage the capacitor. In contrast, mica, ceramic, and plastic-film capacitors are non-polarized and can be connected in either direction without any issues.
45.
Of the following capacitors, which one has the highest dielectric constant?
Correct Answer
C. Glass
Explanation
Glass has the highest dielectric constant among the given options. The dielectric constant is a measure of the ability of a material to store electrical energy in an electric field. A higher dielectric constant indicates that the material can store more electrical energy. Glass has a higher dielectric constant compared to air, mica, and paper, making it the option with the highest dielectric constant.
46.
When the plate area of a capacitor increases,
Correct Answer
A. The capacitance increases
Explanation
When the plate area of a capacitor increases, the capacitance increases. This is because capacitance is directly proportional to the plate area of a capacitor. As the plate area increases, there is more surface area available for the electric field to store charge, resulting in an increase in capacitance.
47.
When the voltage across a capacitor is tripled, the stored charge
Correct Answer
A. Triples
Explanation
When the voltage across a capacitor is tripled, the stored charge also triples. This is because the charge stored in a capacitor is directly proportional to the voltage across it. Therefore, when the voltage is increased by a factor of 3, the stored charge will also increase by the same factor.
48.
When the turns ratio of a transformer is 20 and the primary ac voltage is 12 V, the secondary voltage is
Correct Answer
C. 240 V
Explanation
The secondary voltage of a transformer can be calculated by multiplying the turns ratio with the primary voltage. In this case, the turns ratio is given as 20 and the primary voltage is 12 V. Therefore, the secondary voltage would be 20 times 12 V, which equals 240 V.
49.
A certain transformer has 400 turns in the primary winding and 2,000 turns in the secondary winding. The turns ratio is
Correct Answer
C. 5
Explanation
The turns ratio of a transformer is calculated by dividing the number of turns in the secondary winding by the number of turns in the primary winding. In this case, the transformer has 2,000 turns in the secondary winding and 400 turns in the primary winding. Therefore, the turns ratio is 5.
50.
The mutual inductance when k = 0.65, L_{1} = 2 H, and L_{2} = 5 H is
Correct Answer
B. 2 H
Explanation
The mutual inductance between two coils is given by the formula M = k * sqrt(L1 * L2), where k is the coupling coefficient, L1 is the inductance of the first coil, and L2 is the inductance of the second coil. In this case, k = 0.65, L1 = 2 H, and L2 = 5 H. Plugging these values into the formula, we get M = 0.65 * sqrt(2 * 5) = 0.65 * sqrt(10) ≈ 2 H. Therefore, the correct answer is 2 H.