1.
Inductive reactance is measured in what ?
Correct Answer
E. Ohms
Explanation
Inductive reactance is a measure of the opposition that an inductor presents to the flow of alternating current (AC). It is caused by the inductor's ability to store and release energy in the form of a magnetic field. Reactance is measured in ohms, which is the unit of electrical resistance. Therefore, the correct answer is "Ohms."
2.
RMS power is ?
Correct Answer
B. True power
Explanation
True power refers to the actual power consumed or delivered by an electrical device. It is the power that is converted into useful work or dissipated as heat. True power takes into account both the resistive and reactive components of the load, providing an accurate measure of the power being used. This is different from apparent power, which only considers the magnitude of the power and does not take into account the phase difference between the voltage and current. RMS power, on the other hand, is the root mean square value of the power waveform and is a measure of the average power over time. Therefore, the correct answer for the given question is true power.
3.
How does DC react to a capacitor ?
Correct Answer
C. It is blocked
Explanation
When a DC voltage is applied to a capacitor, it is blocked from flowing through the capacitor. This is because a capacitor allows the flow of AC (alternating current) but blocks the flow of DC (direct current). The capacitor acts as an open circuit for DC voltage, preventing it from passing through. Therefore, the correct answer is "It is blocked."
4.
How many alternations form a cycle ?
Correct Answer
B. 2
Explanation
In this question, the term "alternations" refers to the number of changes or shifts that occur before returning to the original state. A cycle is a complete round or sequence of events. Therefore, the correct answer is 2 because it indicates that there are two alternations required to complete a cycle.
5.
Inductors in series are the same as ?
Correct Answer
D. Resistors in series
Explanation
When inductors are connected in series, their total inductance adds up. This is similar to how resistors in series add up their resistances. In a series circuit, the total resistance or inductance is the sum of the individual values. Therefore, the correct answer is "Resistors in series".
6.
What is the wavelength of a waveform ?(Multiple)
Correct Answer(s)
D. The distance traveled by a waveform during one second
E. The Lambda of a waveform
Explanation
The wavelength of a waveform refers to the distance traveled by the waveform during one second. It represents the spatial length of one complete cycle of the waveform. The term "Lambda" is often used to symbolize the wavelength of a waveform.
7.
The portion of the apparent power caused by inductors and capacitors ?
Correct Answer
C. Reactive power
Explanation
Reactive power refers to the portion of apparent power that is caused by inductors and capacitors in an electrical circuit. Unlike true power, which represents the actual power consumed by the circuit, reactive power does not perform any useful work. Instead, it oscillates between the source and the reactive elements, creating magnetic and electric fields. Reactive power is measured in volt-amperes reactive (VAR) and is necessary for the proper functioning of electrical systems, but it does not contribute to the overall power consumption or energy usage.
8.
In a capacitance circuit what is the relationship of voltage and current ?
Correct Answer
A. Current leads voltage
Explanation
In a capacitance circuit, the current leads the voltage. This means that the current reaches its peak value before the voltage does. This is because in a capacitor, the current flows in response to the changing voltage across it. As the voltage increases, the capacitor charges up and allows more current to flow. Therefore, the current reaches its peak value before the voltage does, resulting in a phase shift between the two.
9.
In an AC circuit with only resistance the current is ?
Correct Answer
A. Always in phase with the voltage
Explanation
In an AC circuit with only resistance, the current is always in phase with the voltage. This means that the current and voltage reach their maximum and minimum values at the same time. This is because in a purely resistive circuit, there is no reactance to cause a phase shift between the current and voltage. Therefore, the current and voltage waveforms are aligned and have the same frequency and shape.
10.
In a capacitive circuit the charge and discharge current must ?
Correct Answer
C. Always be in different directions
Explanation
In a capacitive circuit, the charge and discharge current must always be in different directions. This is because when the capacitor is charging, the current flows in one direction, and when it is discharging, the current flows in the opposite direction. This alternating flow of current is essential for the functioning of the capacitor and the circuit as a whole.
11.
A Farad is a measurement of what ?
Correct Answer
B. Capacitance
Explanation
A Farad is a unit of measurement used to quantify capacitance. Capacitance is the ability of a capacitor to store an electric charge. It is a measure of how much charge can be stored per unit voltage. Therefore, the correct answer is "Capacitance."
12.
The characteristic of an electrical circuit to oppose the change of current flow.
Correct Answer
C. Inductance
Explanation
Inductance is the correct answer because it is the characteristic of an electrical circuit to oppose the change of current flow. Inductance is caused by the presence of an inductor in a circuit, which is a passive electronic component that stores energy in a magnetic field. When the current in a circuit changes, the inductor generates a voltage that opposes this change, resulting in the opposition of current flow. Therefore, inductance is responsible for resisting changes in current flow in an electrical circuit.
13.
Unlike a resistor there is no power dissipation in an ideal ?
Correct Answer
A. Inductor
Explanation
An ideal inductor does not dissipate power because it stores and releases energy in its magnetic field. It does not have any resistance that converts electrical energy into heat.
14.
What is the formula for capacitance reactance ?
Correct Answer
C. XC = 1 / 6.28 x f x c
Explanation
The formula for capacitance reactance is XC = 1 / 6.28 x f x c. This formula is derived from the relationship between capacitance reactance (XC), frequency (f), and capacitance (c). The reciprocal of 6.28 (which is approximately equal to 2π) is used to calculate the reactance. By dividing 1 by the product of 6.28, frequency, and capacitance, we can determine the value of XC. This formula is commonly used in electrical and electronic circuits to calculate the reactance of a capacitor at a given frequency.
15.
What is the period of a waveform with a frequency of 60hz ?
Correct Answer
A. 17 milliseconds
Explanation
The period of a waveform is the time it takes for one complete cycle. The frequency is the number of cycles per second. To find the period, we can take the reciprocal of the frequency. In this case, the frequency is 60Hz, so the period is 1/60 seconds. Converting this to milliseconds, we get 1000/60 milliseconds, which is approximately 16.67 milliseconds. Since none of the given options match exactly, the closest answer is 17 milliseconds.
16.
Capacitors in series are the same as ?
Correct Answer
A. Inductors in parallel
Explanation
When capacitors are connected in series, their total capacitance decreases. This is similar to when inductors are connected in parallel, where their total inductance decreases. Therefore, the correct answer is "Inductors in parallel".
17.
Commercial power is always given in ?
Correct Answer
D. RMS
Explanation
Commercial power is always given in RMS (Root Mean Square) because RMS represents the effective value of an alternating current or voltage. In the case of commercial power, which is typically an AC (alternating current) signal, the RMS value is used to calculate the average power delivered to a load. RMS takes into account both the magnitude and the fluctuation of the signal, providing a more accurate measure of power compared to other options like peak, peak to peak, average, or periodic values.
18.
The power factor is relationship between what to figures ?
Correct Answer
C. True and apparent power
Explanation
The power factor is a measure of how effectively electrical power is being used. It is the ratio of true power (the power actually consumed by the load) to apparent power (the total power supplied to the load). A high power factor indicates efficient utilization of power, while a low power factor indicates wastage of power. Therefore, the relationship between true power and apparent power is important in determining the power factor.
19.
In an inductive circuit what happens when frequency increases ?
Correct Answer
D. There is an increase in inductive reactance
Explanation
When the frequency increases in an inductive circuit, there is an increase in inductive reactance. Inductive reactance is the opposition to the flow of alternating current caused by the inductor in the circuit. As the frequency increases, the inductive reactance also increases, limiting the flow of current through the circuit. This is because the rate of change of current in the inductor becomes greater, resulting in a larger opposition to the current flow.
20.
What is the formula to find RMS voltage ?
Correct Answer
B. RMS = .707 x Peak
Explanation
The formula to find RMS voltage is RMS = .707 x Peak. This formula is derived from the relationship between the RMS value and the peak value of a waveform. The value 0.707 is the square root of 2 divided by 2, which is a constant used to convert the peak value to the RMS value. By multiplying the peak value by 0.707, we can calculate the RMS voltage.
21.
On a current transformer which set of windings always has more turns ?
Correct Answer
D. The secondary
Explanation
The secondary winding of a current transformer always has more turns compared to the primary winding. This is because the primary winding is responsible for carrying the actual current, while the secondary winding is used to measure or monitor the current. In order to step down the current to a manageable level for measurement, the secondary winding needs to have more turns.
22.
How is a current transformer connected ?
Correct Answer
A. In series
Explanation
A current transformer is connected in series with the circuit that carries the current to be measured. By connecting it in series, the current flowing through the transformer is proportional to the current flowing through the circuit. This allows the current transformer to accurately measure and transform high currents to lower, more manageable levels for measurement or protection purposes. Connecting it in parallel or across differing phases would not provide an accurate measurement of the current, while wrapping it around the circuit is not a proper method of connection.
23.
The product of the source voltage and total current ?
Correct Answer
B. Apparent power
Explanation
Apparent power is the product of the source voltage and total current. It represents the total power that is being supplied to a circuit, including both the real power (which is used to perform useful work) and the reactive power (which is used to establish and maintain the electric and magnetic fields in the circuit). Apparent power is measured in volt-amperes (VA) and is important for sizing electrical equipment and determining the capacity of electrical systems.
24.
In an inductive circuit what is the relationship of voltage and current ?
Correct Answer
C. Voltage leads current
Explanation
In an inductive circuit, voltage leads current. This means that the voltage waveform reaches its peak before the current waveform reaches its peak. This is due to the presence of inductance in the circuit, which causes the current to lag behind the voltage. The phase shift between voltage and current in an inductive circuit is typically 90 degrees. This relationship can be observed in devices such as inductors and transformers.
25.
A transformer 400 turns on the primary and 100 turns on the secondary ?
Correct Answer
D. Step down 4:1
Explanation
The given answer, "Step down 4:1," suggests that the transformer is designed to decrease the voltage. This means that the voltage on the primary side is four times higher than the voltage on the secondary side. This step-down ratio indicates that the transformer is intended to reduce the voltage and increase the current, making it suitable for applications where a lower voltage is required.
26.
The power consumed by resistance is ?
Correct Answer
D. True power
Explanation
The correct answer is "True power." True power refers to the actual power consumed by a resistance in a circuit. It is the power that is converted into useful work or dissipated as heat. True power is measured in watts and is calculated by multiplying the voltage across the resistance by the current flowing through it. This is different from reactive power, which represents the power that oscillates between the source and the load due to the presence of inductance and capacitance in the circuit.
27.
True power is the product of resistance and ?
Correct Answer
B. Current squared
Explanation
The correct answer is "Current squared." In electrical circuits, true power is calculated by multiplying the resistance of the circuit by the square of the current flowing through it. This is known as the formula for power, P = I^2 * R, where P represents power, I represents current, and R represents resistance. Therefore, the product of resistance and current squared gives the true power in a circuit.
28.
The period of a waveform is the inverse of what ?
Correct Answer
C. Frequency
Explanation
The period of a waveform represents the time it takes for one complete cycle of the waveform to occur. Therefore, it is the inverse of the frequency, which measures the number of cycles per second. As frequency increases, the period decreases, and vice versa.
29.
What is resonance ?
Correct Answer
E. Inductive reactance is equal to capacitance reactance
Explanation
Resonance refers to a condition in an electrical circuit where the inductive reactance is equal to the capacitance reactance. This means that the impedance of the circuit is at its minimum value, resulting in a higher current flow. At resonance, the energy exchange between the inductor and capacitor is at its maximum, leading to a more efficient transfer of power.
30.
What is the formula for inductive reactance ?
Correct Answer
D. XL = 6.28 x f x l
Explanation
The formula for inductive reactance is XL = 6.28 x f x l. This formula calculates the inductive reactance (XL) by multiplying the frequency (f) with 6.28 (which is approximately equal to 2π) and the inductance (l). The inductive reactance represents the opposition to the flow of alternating current in an inductor, and it increases with the increase in frequency and inductance.
31.
Total capacitance of a two 40 microfarad capacitors
Correct Answer
D. 20
Explanation
The total capacitance of two capacitors connected in parallel is given by the sum of their individual capacitances. In this case, the two capacitors have a capacitance of 40 microfarads each. Therefore, when they are connected in parallel, the total capacitance is 40 microfarads + 40 microfarads = 80 microfarads.
32.
At resonance what happens to resistance ?
Correct Answer
A. Nothing
Explanation
At resonance, the resistance in a circuit remains unchanged. This is because resonance occurs when the inductive reactance and the capacitive reactance cancel each other out, resulting in a purely resistive circuit. Therefore, the resistance does not increase or decrease but stays the same.
33.
In a transformer how is the frequency when crossing the coils ?
Correct Answer
D. Stays the same
Explanation
The frequency stays the same when crossing the coils in a transformer because the primary and secondary coils are connected magnetically, not electrically. The coils are wound around a common core, and the alternating current passing through the primary coil induces a magnetic field in the core. This magnetic field then induces a current in the secondary coil, resulting in the same frequency as the primary coil. Therefore, the frequency remains constant throughout the transformer.
34.
What is the peek voltage of a 120Vac circuit ?
Correct Answer
D. 170 volts
35.
What is the formula to find the average voltage ?
Correct Answer
D. Average = Peak x .637
Explanation
The formula to find the average voltage is given by Average = Peak x .637. This formula suggests that to calculate the average voltage, you need to multiply the peak voltage value by 0.637.
36.
Total opposition of current flow in a circuit ?
Correct Answer
B. Impedance
Explanation
Impedance refers to the total opposition of current flow in a circuit. It is a combination of resistance, which is the opposition to the flow of current in a circuit, and reactance, which is the opposition to the change in current flow caused by inductors or capacitors. Therefore, impedance encompasses both resistive and reactive components and represents the overall opposition to current flow in a circuit.
37.
A transformer in which the primary and secondary voltages are out of phase ?
Correct Answer
E. Unlike-wound
Explanation
An unlike-wound transformer is a type of transformer where the primary and secondary windings are wound in opposite directions. This results in a phase shift between the primary and secondary voltages. When the primary voltage is at its maximum, the secondary voltage will be at its minimum, and vice versa. This phase shift can be useful in certain applications where a specific phase relationship between the primary and secondary voltages is required.
38.
Total inductive reactance of a 25 henry inductor in a 60 Hz circuit ?
Correct Answer
D. 9420 ohms
Explanation
The total inductive reactance of an inductor in a circuit is given by the formula Xl = 2πfL, where Xl is the inductive reactance, f is the frequency, and L is the inductance. In this case, the inductance is given as 25 henries and the frequency is 60 Hz. Plugging these values into the formula, we get Xl = 2π(60)(25) = 9420 ohms. Therefore, the correct answer is 9420 ohms.
39.
What is the frequency of a waveform that repeats 10 times in a half second ?
Correct Answer
B. 20 Hz
Explanation
The frequency of a waveform is the number of times it repeats per unit of time. In this case, the waveform repeats 10 times in a half second. To find the frequency, we divide the number of repetitions (10) by the time period (0.5 seconds). Therefore, the frequency is 10/0.5 = 20 Hz. Therefore, the correct answer is 20 Hz.
40.
A Henry is a measurement of what ?
Correct Answer
D. Impedance
Explanation
A Henry is a measurement of impedance. Impedance refers to the total opposition to the flow of alternating current in a circuit, including both resistance and reactance. It is measured in ohms and is represented by the symbol Z. The unit Henry is specifically used to measure inductance, which is a type of reactance caused by the presence of an inductor in a circuit. Therefore, the correct answer is impedance.