Alternating Current Class 12 Case Study Questions Physics Chapter 7

Reading Time: 8 minutes

Last Updated on December 26, 2024 by XAM CONTENT

Hello students, we are providing case study questions for class 12 physics. Case study questions are the new question format that is introduced in CBSE board. The resources for case study questions are very less. So, to help students we have created chapterwise case study questions for class 12 physics. In this article, you will find case study questions for cbse class 12 physics chapter 7 Alternating Current.

Chapter	Alternating Current
Type of Questions	Case Study Questions
Nature of Questions	Competency Based Questions
Board	CBSE
Class	12
Subject	Physics
Unit	Unit 4 Electromagnetic Induction and Alternating Currents
Useful for	Class 12 Studying Students
Answers provided	Yes
Difficulty level	Mentioned
Important Link	Class 12 Physics Chapterwise Case Study

Case Study Questions on Alternating Current

Questions

Question 1:

An $L C$ circuit also called a resonant circuit or tank circuit or tuned circuit, is an electric circuit consisting of an inductor represented by the letter $L$ and a capacitor, represented by the letter $C$ connected together. An $L C$ circuit is an idealised model since it assumes there is no dissipation of energy due to resistance.

An $L C$ circuit contains a 20 mH inductor and a $50 \mu \mathrm{~F}$ capacitor with an initial charge of 10 mC . The resistance of the circuit is negligible. Let the instant of circuit is closed be $t=0$.

Read the given passage carefully and give the answer of the following questions:

Q 1. What will be the total energy stored initially?

Q 2. What will be the natural frequency of the circuit?

Q 3. At what time is the energy stored completely electrical?

Q 4. At what time is the energy stored completely magnetic?

Q 5. Calculate the value of X_L.

Answers

1. Energy, $E=\frac{1}{2} \frac{Q_0^2}{C}=\frac{\left(10 \times 10^{-3}\right)^2}{2 \times 50 \times 10^{-6}}=1 \mathrm{~J}$

2. Frequency, $v=\frac{1}{2 \pi \sqrt{L C}}=\frac{1}{2 \pi \sqrt{20 \times 10^{-3} \times 50 \times 10^{-6}}}$

$$
=\frac{10^3}{2 \pi}=159.24 \mathrm{~Hz}
$$

3. Period of one complete cycle

$$
T=\frac{1}{v}=\frac{2 \pi}{10^3}=6.28 \mathrm{~ms}
$$

At $t=0, Q=Q_0=10 \mathrm{mC}$
$\therefore$ Oscillatory charge at time $t$ is

$$
Q=Q_0 \cos \frac{2 \pi}{T} t
$$

For energy stored as electrical, we can write $Q= \pm Q_0$.

$$
\begin{aligned}
& \Rightarrow \quad \pm Q_0=Q_0 \cos \frac{2 \pi t}{T} \Rightarrow \cos \frac{2 \pi t}{T}= \pm 1 \\
& \Rightarrow \quad \frac{2 \pi t}{T}=n \pi \Rightarrow t=\frac{n T}{2}, n=0,1,2,3
\end{aligned}
$$

Hence, energy stored in the capacitor is completely electrical at $t=0, \frac{T}{2}, T, \frac{3 T}{2}, \ldots$.

4. Magnetic energy is maximum when electrical energy is equal to zero i.e., when Q = 0

$$
\begin{array}{ll}
\Rightarrow & \cos \frac{2 \pi t}{T}=0 \Rightarrow \frac{2 \pi t}{T}=\frac{(2 n+1) \pi}{2} \\
\Rightarrow & t=\frac{(2 n+1) T}{4} \\
\text { Hence, } & t=\frac{T}{4}, \frac{3 T}{4}, \frac{5 T}{4}, \cdots \cdots .
\end{array}
$$

5.

$$
\begin{aligned}
X_L & =\omega L=2 \pi v L \\
& =2 \times \pi \times \frac{10^3}{2 \neq} \times 20 \times 10^{-3} \\
\Rightarrow \quad X_L & =20 \Omega
\end{aligned}
$$

Also check

Case study questions for other chapters of class 12 physics is given below.

• Semiconductor Electronics Class 12 Case Study Questions Physics Chapter 14
• Nuclei Class 12 Case Study Questions Physics Chapter 13
• Atoms Class 12 Case Study Questions Physics Chapter 12
• Dual Nature of Radiation and Matter Class 12 Case Study Questions Physics Chapter 11
• Wave Optics Class 12 Case Study Questions Physics Chapter 10
• Ray Optics and Optical Instruments Class 12 Case Study Questions Physics Chapter 9
• Electromagnetic Waves Class 12 Case Study Questions Physics Chapter 8
• Alternating Current Class 12 Case Study Questions Physics Chapter 7
• Electromagnetic Induction Class 12 Case Study Questions Physics Chapter 6
• Magnetism and Matter Class 12 Case Study Questions Physics Chapter 5
• Moving Charges and Magnetism Class 12 Case Study Questions Physics Chapter 4
• Current Electricity Class 12 Case Study Questions Physics Chapter 3
• Electrostatic Potential and Capacitance Class 12 Case Study Questions Physics Chapter 2
• Electric Charges and Fields Class 12 Case Study Questions Physics Chapter 1
• Case Study Questions for Class 12 Physics

We hope the given case study questions for Alternating Current Class 12 helps you in your learning.

Download eBooks for CBSE Class 12 Physics (Exam Special)

• 120 Case Study Questions for Class 12 Physics
• 320 Assertion Reasoning Questions for Class 12 Physics
• 95 Reasoning Based Questions for Class 12 Physics
• Important Derivation for Class 12 Physics
• MCQ Questions for Class 12 Physics
• Chapter Test for Class 12 Physics with Solutions
• 230 Important Numerical for Class 12 Physics
• 75 Important Diagrams & Graphs for Class 12 Physics

Topics from which case study questions may be asked

• Alternating Currents
• Peak and RMS Value of Alternating Current/Voltage
• Reactance and Impedance
• LCR Series Circuit (Phasors Only)
• Resonance in AC Circuits
• Power in AC Circuits
• Power Factor
• Wattless Current
• AC Generator
• Transformer

Two electric field lines never cross each other. If they intersect, then there will be two directions of electric field at the point of intersection which is not possible.

For further practice on case study questions related to Alternating Current Class 12 Physics, we recommend exploring the link given below.

Frequently Asked Questions (FAQs) on Alternating Current Case Study Questions