MCQs Based On Alternating Current

Ans. a) Admittance

Explanation: Admittance is an indicator of the ease with which a connection or mechanism permits a current to pass. Impedance is the resistance presented by a connection to a flow when a value is given. Comparing admittance and impedance, admittance is the opposite (inverse) of impedance. Consequently, it serves the opposite purpose of resistance. Consequently, admittance is described as the inverse of impedance, similar to how conductivity and resistance are described.

Ans. d) Zero is the average value of a whole cycle.

Explanation: A.C. current has alternating values, the average amount of current for a whole period is zero, and actual speeds are between 50 and 60 hertz, meaning it switches indications more than 100 times per sec, which isn't really apparent on D.C. ammeters.

An alternating current is a cyclic current, which implies that its cycle resumes after a fixed amount of time. Occasionally, or after a fixed amount of space, its polarity is reversed. The alternating current has a positive electrical charge during the first half cycle and negative polarity during the second half cycle. The maximum integer figure in both orientations is the same. Consequently, the mean result of an alternating current phase is usually zero.

Ans. b) 50 Hz 

Explanation: The primary reason for the Indian power supply norm of 220-250 Volts and 50 Hz is because the Indian temperature is greater and high intensity might heat cabling, etc. In the mountainous region in the north, the weather is low. However, we cannot alter the wavelength of the energy to 60Hz since we would also need to update the specifications for all electronic systems.

50Hz requires a voltage range of 220 to 250 volts, whereas 60Hz requires less voltage. Places like the United States use 60 Hz. So that all electrical equipment is necessary to keep 60 Hz.

Ans. b) Dynamo

Explanation: Alternators and dynamos are the two most common forms of electromagnetic converters. Dynamos employ commutators to generate pulsing direct energy. The basic practicable generator consists of a revolving rectangular coil in a magnetic force of constant intensity. A persistent magnet typically supplies the magnetic field. When a wire coil spins inside a magnetic force, magnetic energy passes through it. As a result, the generated potential changes with each half revolution, producing an alternating current.

Ans. a) increases

Explanation: In accordance with Lenz's law, an inductor resists the passage of power through it by generating a generated emf. The generated voltage has an orientation that maintains the actual value of the stream. If the current is dropping, the produced emf will have the opposite polarity to raise the flow, and vice versa. As the induced emf is proportionate to the pace of variation of current, it will give stronger reactance to the flow of electricity when the rate of shift is quicker, i.e., when the frequency is larger. Hence, the reactance of inductance is equal to the wavelength.

Ans. b) Decreases

Explanation: The Q factor is the ratio of energy conserved each cycle to energy lost per cycle. The greater the Q factor, the more electricity can be retained. The quality factor regulates oscillation dampening. Underdamping occurs when the Q factor is less than 50 percent. The quality factor in an LCR loop measures the crispness of an LCR circuit. It is a number without dimensions. The greater the resonance's intensity, the finer the Q factor. In a series-connected circuitry, recurrence happens when the source frequency equalizes the voltage between the inductor and capacitor.

Ans. a) effective resistance due to capacity

Explanation: Similar to resistance, capacitive reactance is evaluated in ohms of the resistor and is dependent on the rate of the voltage source and the capacitor's magnitude. In an AC circuit, the capacitor is continually charged and released. The capacitor loads and releases as the Ac source voltage rises and falls. We are aware that the power flowing through a capacitor opposes the rate of increase of the input load. Similar to a resistive, the capacitance in an AC circuit provides resistance to the passage of electricity.

Ans. (c) Pure resistor

Explanation: When an alternating current flows through an electrical system, a phase mismatch between the voltage and stream develops. This phase shift is contingent upon the sort of load linked to the circuit. This phase difference is reflected by the power factor.

Consequently, the active power is only the cosine of the ratio between volts and flow. If an alternating circuit consists of a single pure resistor, it is a completely resistive connection. No matter whether the form of energy (AC or DC) is provided to a completely resistive circuitry, the current will always move in phase with the input signal since the resistor exhibits the same properties for both types of supply.

Ans. c) R only

Explanation: There is always an energy loss in RLC circuits dependent on the nature of the components and the operating electrical parameters. In an LCR circuitry, energy is dissipated only via the resistance since the phase shift between the current and volts is zero. A resistor is a mechanism that resists the passage of current through it, and resistance includes the conversion of electrical potential into thermal energy. The decline in resistance is equivalent to the stream and, thus, to the power dissipation on the transistor.

Ans. a) Series Resonant Circuit

Explanation: The series resonant circuit is often referred to as an 'acceptor' circuit. By providing the lowest possible resistance to the stream at the harmonic resonance, it is able to choose or accept one specific frequency above others. Because during resonance, the circuit's resistivity is at its lowest. Therefore, merely take the flow whose frequency corresponds to its frequency range, or we may say that it operates mostly at equilibrium.

At its frequency responsiveness, the acceptor circuit gives the highest responsiveness to currents. As a sequential resonance circuit, the only purpose of radiation characteristics and acceptor circuit resistance is minimal, but the voltage may be amplified.

Ans. a) Impedance is very high

Explanation: An inductor and capacitors are connected to one another in a parallel resonant circuit. Additionally, a generator of alternating current is connected to this concurrent combination of attributes. High resistance in the parallel resonant circuitry has the impact of causing the circuitry to deny the wavelength of the incoming ac voltage that is identical to the resonant frequency.

This occurs when the wavelength of the input ac electrical equals the resonant frequency. Due to the fact that this attribute may be used to both enable and disable the passage of current at a certain frequency across a circuitry, this circuit is utilized as a rejector loop.

Ans. c) Mutual Induction

Explanation: The Voltage Transformer is an electrical element, as opposed to an electrical component. A converter is essentially a static (or immobile) passive electromagnetic electronic appliance. Using Faraday's rule of induction, this device converts electrical power from one number to another.

The transformer does this by connecting two or more electronic circuits through a time-varying magnetic circuit formed by the generator itself. The operation of a transformer is based on electromagnetic induction in the manner of Mutual Induction. Mutual induction is the technique by which one wire coil magnet generates a voltage into a nearby coil. Therefore, transformers operate in the "magnetic field." Transformers are so-called because they "change" one voltage or flow level into another.

Ans. b) 1.57 A

Explanation: Given

• Capacitance, C = 50 μF = 50 x 10^-6 F
• rms voltage, V_rms = 100 V
• Frequency of alternating supply, f = 50 Hz

Capacitive reactance, X_C = 1/2πfC = 1/(2 x 3.14 x 50 x 50 x 10^-6) = 63.69 ohm

Now, I_rms = V_rms / X_C = 100/63.69 = 1.57 A

Ans. a) 12.74 A

Explanation: Given

• Inductance, L = 50 mH = 50 x 10^-3 H
• rms voltage, V_rms = 200 V
• Frequency of alternating supply, f = 50 Hz

Inductive reactance, X_L = 2πfL = 2 x 3.14 x 50 x 50 x 10^-3 = 15.7 ohm

Now, I_rms = V_rms / X_L = 200/15.7 = 12.74 A