# 31 Lecture

## PHY101

### Midterm & Final Term Short Notes

## Alternating Current

Alternating current (AC) is a type of electrical current that periodically reverses direction, unlike direct current (DC), which flows in only one direction. AC is widely used in power generation, transmission, and distribution systems, as well

**Important Mcq's**

Midterm & Finalterm Prepration

Past papers included

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**What is the phase difference between voltage and current in an ideal inductor in an AC circuit?**

A. 0 degrees

B. 90 degrees

C. 180 degrees

D. 270 degrees

**Answer: B. 90 degrees**

**What is the unit of frequency in an AC circuit?**

A. Hertz

B. Volt

C. Ampere

D. Ohm

**Answer: A. Hertz**

**What is the term for the opposition of an AC circuit to the flow of current?**

A. Resistance

B. Reactance

C. Impedance

D. Conductance

**Answer: B. Reactance**

**Which of the following components is commonly used to reduce the reactance of an AC circuit?**

A. Resistor

B. Capacitor

C. Inductor

D. Transformer

**Answer: B. Capacitor**

**What is the effect of increasing the frequency of an AC circuit?**

A. Increases the reactance of inductors

B. Decreases the reactance of inductors

C. Increases the reactance of capacitors

D. Decreases the reactance of capacitors

**Answer: B. Decreases the reactance of inductors**

**What is the term for the measure of the amount of AC power being used in a circuit?**

A. Amplitude

B. Frequency

C. Power factor

D. RMS voltage

A**nswer: C. Power factor**

**What is the relationship between the voltage and current in a purely resistive AC circuit?**

A. They are in phase

B. Voltage leads current by 90 degrees

C. Voltage lags current by 90 degrees

D. Voltage and current are 180 degrees out of phase

**Answer: A. They are in phase**

**Which of the following is true for a parallel AC circuit?**

A. Voltage is the same across all components

B. Current is the same across all components

C. Resistance increases as more components are added

D. Capacitance decreases as more components are added

**Answer: A. Voltage is the same across all components**

**What is the unit of power in an AC circuit?**

A. Watt

B. Volt-ampere

C. Ohm

D. Joule

**Answer: B. Volt-ampere**

**What is the term for the time delay between the peak voltage and peak current in an AC circuit?**

A. Phase angle

B. Power factor

C. Impedance

D. Reactance

**Answer: A. Phase angle**

**Subjective Short Notes**

Midterm & Finalterm Prepration

Past papers included

Download PDF
**What is meant by alternating current?**

Answer: Alternating current is an electric current that periodically reverses direction, constantly changing its magnitude and direction.

**What is the frequency of AC current in India?**

Answer: The frequency of AC current in India is 50 Hz.

**Define RMS value of AC current.**

Answer: RMS (Root Mean Square) value of AC current is the value of the current which when passed through a resistor for a given time produces the same amount of heat as produced by the corresponding DC current when passed for the same time through the same resistor.

**What is the phase difference between the voltage and current in a purely resistive circuit?**

Answer: In a purely resistive circuit, the voltage and current are in phase with each other, i.e., there is no phase difference between them.

**What is an inductor in an AC circuit?**

Answer: An inductor is a passive electrical component that stores energy in a magnetic field when electric current flows through it in an AC circuit.

**What is the reactance of a capacitor in an AC circuit?**

Answer: The reactance of a capacitor in an AC circuit is given by Xc = 1/(2?fC), where f is the frequency of the AC signal and C is the capacitance of the capacitor.

**What is the power factor of a purely resistive circuit?**

Answer: The power factor of a purely resistive circuit is unity or 1.

**What is meant by the resonance frequency of an AC circuit?**

Answer: The resonance frequency of an AC circuit is the frequency at which the circuit offers maximum impedance to the flow of current.

**What is the phase difference between the voltage and current in an inductive circuit?**

Answer: In an inductive circuit, the current lags behind the voltage by 90 degrees.

**What is an LC circuit?**

Answer: An LC circuit is a resonant circuit consisting of an inductor (L) and a capacitor (C) connected together. It can store electrical energy oscillating at its resonant frequency.