#### Chapters

Chapter 2: Kinetic Theory of Gases

Chapter 3: Calorimetry

Chapter 4: Laws of Thermodynamics

Chapter 5: Specific Heat Capacities of Gases

Chapter 6: Heat Transfer

Chapter 7: Electric Field and Potential

Chapter 8: Gauss’s Law

Chapter 9: Capacitors

Chapter 10: Electric Current in Conductors

Chapter 11: Thermal and Chemical Effects of Current

Chapter 12: Magnetic Field

Chapter 13: Magnetic Field due to a Current

Chapter 14: Permanent Magnets

Chapter 15: Magnetic Properties of Matter

Chapter 16: Electromagnetic Induction

Chapter 17: Alternating Current

Chapter 18: Electromagnetic Waves

Chapter 19: Electric Current through Gases

Chapter 20: Photoelectric Effect and Wave-Particle Duality

Chapter 21: Bohr’s Model and Physics of Atom

Chapter 22: X-rays

Chapter 23: Semiconductors and Semiconductor Devices

Chapter 24: The Nucleus

Chapter 25: The Special Theory of Relativity

#### HC Verma Concepts of Physics - Vol. 2

## Chapter 17: Alternating Current

#### HC Verma solutions for Class 11 Physics Chapter 17 Exercise Short Answers [Pages 328 - 329]

What is the reactance of a capacitor connected to a constant DC source?

The voltage and current in a series AC circuit are given by V = V_{0}cos ω*t* and *i* = *i*_{0} sin ω*t*. What is the power dissipated in the circuit?

Two alternating currents are given by `i_1 = i_0 sin wt and i_2 = i_0 sin (wt + pi/3)` Will the rms values of the currents be equal or different?

Can the peak voltage across the inductor be greater than the peak voltage of the source in an LCR circuit?

In a circuit, containing a capacitor and an AC source, the current is zero at the instant the source voltage is maximum. Is it consistent with Ohm's Law?

An AC source is connected to a capacitor. Will the rms current increase, decrease or remain constant if a dielectric slab is inserted into the capacitor?

When the frequency of the AC source in an LCR circuit equals the resonant frequency, the reactance of the circuit is zero. Does it mean that there is no current through the inductor or the capacitor?

When an AC source is connected to a capacitor, there is a steady-state current in the circuit. Does it mean that the charges jump from one plate to the other to complete the circuit?

A current *i*_{1} = *i*_{0} sin ω*t* passes through a resistor of resistance R. How much thermal energy is produced in one time period? A current* **i*_{2} = −*i*_{0} sin ω*t* passes through the resistor. How much thermal energy is produced in one time period? If *i*_{1} and *i*_{2} both pass through the resistor simultaneously, how much thermal energy is produced? Is the principle of superposition obeyed in this case?

Is energy produced when a transformer steps up the voltage?

A transformer is designed to convert an AC voltage of 220 V to an AC voltage of 12 V. If the input terminals are connected to a DC voltage of 220 V, the transformer usually burns. Explain.

Can you have an AC series circuit in which there is a phase difference of (a) 180° (b) 120° between the emf and the current?

A resistance is connected to an AC source. If a capacitor is included in the series circuit, will the average power absorbed by the resistance increase or decrease? If an inductor of small inductance is also included in the series circuit, will the average power absorbed increase or decrease further?

Can a hot-wire ammeter be used to measure a direct current of constant value? Do we have to change the graduations?

#### HC Verma solutions for Class 11 Physics Chapter 17 Exercise MCQ [Page 329]

A capacitor acts as an infinite resistance for

DC

DC

DC as well as AC

neither AC nor DC

An AC source producing emf ε = ε_{0} [cos (100 π s^{−1})*t* + cos (500 π s^{−1})*t*] is connected in series with a capacitor and a resistor. The steady-state current in the circuit is found to be *i *= *i*_{1} cos [(100 π s^{−1})*t* + φ_{1}) + *i*_{2} cos [(500π s^{−1})*t* + ϕ_{2}]. So,

*i*_{1}>*i*_{2}*i*_{1}=*i*_{2}*i*_{1}<*i*_{2}The information is insufficient to find the relation between

*i*_{1}and*i*_{2}.

The peak voltage of a 220 V AC source is

220 V

about 160 V

about 310 V

440 V

An AC source is rated 220 V, 50 Hz. The average voltage is calculated in a time interval of 0.01 s. It

must be zero

may be zero

is never zero

`is (220//sqrt2 )V`

The magnetic field energy in an inductor changes from maximum to minimum value in 5.0 ms when connected to an AC source. The frequency of the source is

20 Hz

50 Hz

200 Hz

500 Hz

Which of the following plots may represent the reactance of a series LC combination?

A series AC circuit has a resistance of 4 Ω and a reactance of 3 Ω. The impedance of the circuit is

5 Ω

7 Ω

12/7 Ω

7/12 Ω

Transformers are used

in DC circuits only

in AC circuits only

in both DC and AC circuits

neither in DC nor in AC circuits

An alternating current is given by *i* =* **i*_{1} cos ω*t* + *i*_{2} sin ω*t*. The rms current is given by

`(l_1 +l_2)/sqrt2`

`|i_1 + i_2|/sqrt2`

`sqrt(i_1^2 + i_2^2)/2`

`sqrt(i_1^2+i_2^2)/sqrt2`

An alternating current of peak value 14 A is used to heat a metal wire. To produce the same heating effect, a constant current *i* can be used, where *i* is

14 A

about 20 A

7 A

about 10 A

A constant current of 2.8 A exists in a resistor. The rms current is

2.8 A

about 2 A

1.4 A

undefined for a direct current

#### HC Verma solutions for Class 11 Physics Chapter 17 Exercise MCQ [Pages 329 - 330]

An inductor, a resistance and a capacitor are joined in series with an AC source. As the frequency of the source is slightly increased from a very low value, the reactance

of the inductor increases

of the resistor increases

of the capacitor increases

of the circuit increases

The reactance of a circuit is zero. It is possible that the circuit contains

(a) an inductor and a capacitor

(b) an inductor but no capacitor

(c) a capacitor but no inductor

(d) neither an inductor nor a capacitor

In an AC series circuit, the instantaneous currt is zero when the instantaneous voltage is maximum. Connected to the source may be a

(a) pure inductor

(b) pure capacitor

(c) pure resistor

(d) combination of an inductor and a capacitor

An inductor coil of some resistance is connected to an AC source. Which of the following quantities have zero average value over a cycle?

(a) Current

(b) Induced emf in the inductor

(c) Joule heat

(d) Magnetic energy stored in the inductor

The AC voltage across a resistance can be measured using

a potentiometer

a hot-wire voltmeter

a moving-magnet galvanometer

To convert mechanical energy into electrical energy, one can use

(a) DC dynamo

(b) AC dynamo

(c) motor

(d) transformer

An AC source rated 100 V (rms) supplies a current of 10 A (rms) to a circuit. The average power delivered by the source

(a) must be 1000 W

(b) may be 1000 W

(c) may be greater than 1000 W

(d) may be less than 1000 W

#### HC Verma solutions for Class 11 Physics Chapter 17 [Pages 33 - 331]

Find the time required for a 50 Hz alternating current to change its value from zero to the rms value.

The household supply of electricity is at 220 V (rms value) and 50 Hz. Find the peak voltage and the least possible time in which the voltage can change from the rms value to zero.

A bulb rated 60 W at 220 V is connected across a household supply of alternating voltage of 220 V. Calculate the maximum instantaneous current through the filament.

An electric bulb is designed to operate at 12 volts DC. If this bulb is connected to an AC source and gives normal brightness, what would be the peak voltage of the source?

The peak power consumed by a resistive coil, when connected to an AC source, is 80 W. Find the energy consumed by the coil in 100 seconds, which is many times larger than the time period of the source.

The dielectric strength of air is 3.0 × 10^{6} V/m. A parallel-plate air-capacitor has area 20 cm^{2} and plate separation 0.10 mm. Find the maximum rms voltage of an AC source that can be safely connected to this capacitor.

The current in a discharging LR circuit is given by* i* = *i*_{0}_{ }*e*^{−t/τ} , where τ is the time constant of the circuit. Calculate the rms current for the period *t *= 0 to *t* = τ.

A capacitor of capacitance 10 μF is connected to an oscillator with output voltage ε = (10 V) sin ωt. Find the peak currents in the circuit for ω = 10 s^{−1}, 100 s^{−1}, 500 s^{−1} and 1000 s^{−1}.

A coil of inductance 5.0 mH and negligible resistance is connected to the oscillator of the previous problem. Find the peak currents in the circuit for ω = 100 s^{−1}, 500 s^{−1}, 1000 s^{−1}.

A coil has a resistance of 10 Ω and an inductance of 0.4 henry. It is connected to an AC source of 6.5 V, `30/pi Hz`. Find the average power consumed in the circuit.

A resistor of resistance 100 Ω is connected to an AC source ε = (12 V) sin (250 π *s*^{−1})*t*. Find the energy dissipated as heat during *t* = 0 to *t* = 1.0 ms.

In a series RC circuit with an AC source, R = 300 Ω, C = 25 μF, ε_{0} = 50 V and ν = 50/π Hz. Find the peak current and the average power dissipated in the circuit.

An electric bulb is designed to consume 55 W when operated at 110 volts. It is connected to a 220 V, 50 Hz line through a choke coil in series. What should be the inductance of the coil for which the bulb gets correct voltage?

In a series LCR circuit with an AC source, R = 300 Ω, C = 20 μF, L = 1.0 henry, ε_{rms} = 50 V and ν = 50/π Hz. Find (a) the rms current in the circuit and (b) the rms potential difference across the capacitor, the resistor and the inductor. Note that the sum of the rms potential differences across the three elements is greater than the rms voltage of the source.

Consider the situation of the previous problem. Find the average electric field energy stored in the capacitor and the average magnetic field energy stored in the coil.

An inductance of 2.0 H, a capacitance of 18μF and a resistance of 10 kΩ are connected to an AC source of 20 V with adjustable frequency. (a) What frequency should be chosen to maximise the current in the circuit? (b) What is the value of this maximum current?

An inductor-coil, a capacitor and an AC source of rms voltage 24 V are connected in series. When the frequency of the source is varied, a maximum rms current of 6.0 A is observed. If this inductor coil is connected to a battery of emf 12 V and internal resistance 4.0 Ω, what will be the current?

Following figure shows a typical circuit for a low-pass filter. An AC input V_{i }= 10 mV is applied at the left end and the output V_{0} is received at the right end. Find the output voltage for ν = 10 k Hz, 1.0 MHz and 10.0 MHz. Note that as the frequency is increased the output decreases and, hence, the name low-pass filter.

A transformer has 50 turns in the primary and 100 in the secondary. If the primary is connected to a 220 V DC supply, what will be the voltage across the secondary?

## Chapter 17: Alternating Current

#### HC Verma Concepts of Physics - Vol. 2

## HC Verma solutions for Class 11 Physics chapter 17 - Alternating Current

HC Verma solutions for Class 11 Physics chapter 17 (Alternating Current) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CBSE Concepts of Physics - Vol. 2 solutions in a manner that help students grasp basic concepts better and faster.

Further, we at Shaalaa.com provide such solutions so that students can prepare for written exams. HC Verma textbook solutions can be a core help for self-study and acts as a perfect self-help guidance for students.

Concepts covered in Class 11 Physics chapter 17 Alternating Current are Lc Oscillations, Reactance and Impedance, Peak and Rms Value of Alternating Current Or Voltage, Alternating Currents, Power in Ac Circuit: the Power Factor, Ac Voltage Applied to a Series Lcr Circuit, Ac Voltage Applied to an Inductor, Representation of Ac Current and Voltage by Rotating Vectors - Phasors, Ac Voltage Applied to a Resistor, Alternating Currents and Direct Currents, Forced Oscillations and Resonance, Ac Voltage Applied to a Capacitor, Transformers.

Using HC Verma Class 11 solutions Alternating Current exercise by students are an easy way to prepare for the exams, as they involve solutions arranged chapter-wise also page wise. The questions involved in HC Verma Solutions are important questions that can be asked in the final exam. Maximum students of CBSE Class 11 prefer HC Verma Textbook Solutions to score more in exam.

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