12th Physics - Book Back Answers - Unit 4 Electromagnetic Induction and Alternating Current - English Medium Guides

  

 

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Tamil Nadu Board 12th Standard Physics - Unit 4: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Unit 4 from the Tamil Nadu State Board 12th Standard Physics textbook. These detailed answers have been carefully prepared by our expert teachers at KalviTips.com.

    We have explained each answer in a simple, easy-to-understand format, highlighting important points step by step under the relevant subtopics. Students are advised to read and memorize these subtopics thoroughly. Once you understand the main concepts, you’ll be able to connect other related points with real-life examples and confidently present them in your tests and exams.

    By going through this material, you’ll gain a strong understanding of Unit 4 along with the corresponding book back questions and answers (PDF format).

Question Types Covered:

• 1 Mark Questions: Choose the correct answer, Fill in the blanks, Identify the correct statement, Match the following 
• 2 Mark Questions: Answer briefly 
• 3, 4, and 5 Mark Questions: Answer in detail

All answers are presented in a clear and student-friendly manner, focusing on key points to help you score full marks.

All the best, Class 12 students! Prepare well and aim for top scores. Thank you!

I. Multiple choice questions.

1. An electron moves on a straight line path XY as shown in the figure. The coil abcd is adjacent to the path of the electron. What will be the direction of current, if any, induced in the coil?

(a) The current will reverse its direction as the electron goes past the coil
(b) No current will be induced
(c) abcd
(d) adcb

Answer Key:

(a) The current will reverse its direction as the electron goes past the coil

  

2. A thin semi-circular conducting ring (PQR) of radius r is falling with its plane vertical in a horizontal magnetic field B, as shown in the figure.

The potential difference developed across the ring when its speed v , is

(a) Zero

(b) $\frac{\mathbf{B}\mathbf{v}\mathbf{\pi }{\mathbf{r}}^{\mathbf{2}}}{\mathbf{2}}$ and P is at higher potential

(c) $\frac{\mathbf{\pi }}{}$rBv and R is at higher potential
(d) 2rBv and R is at higher potential

Answer Key:

(d) 2rBv and R is at higher potentia 

  
3. The flux linked with a coil at any instant t is given by ${\mathrm{\Phi }}_{\mathrm{B}}=10{\mathrm{t}}^2$ − 50t + 250 . The induced emf at t = 3 s is
(a) −190 V 

(b) −10 V
(c) 10 V 

(d) 190 V

Answer Key:

(b) −10 V 

  
4. When the current changes from +2A to −2A in 0.05 s, an emf of 8 V is induced in a coil. The co-efficient of self-induction of the coil is
(a) 0.2 H 

(b) 0.4 H
(c) 0.8 H 

(d) 0.1 H

Answer Key:

(b) 0.4 H 

  
5. The current i flowing in a coil varies with time as shown in the figure. The variation of induced emf with time would be 

 

(a) 

(b) 

(c) 

(d) 

 

Answer Key:

(a) 

  

6. A circular coil with a cross-sectional area of 4 $\mathbf{c}{\mathbf{m}}^{\mathbf{2}}$ has 10 turns. It is placed at the centre of a long solenoid that has 15 turns/cm and a cross-sectional area of $\mathbf{c}{\mathbf{m}}^{\mathbf{2}}$. The axis of the coil coincides with the axis of the solenoid. What is their mutual inductance?
(a) 7.54 μH 

(b) 8.54 μH
(c) 9.54 μH 

(d) 10.54 μH

Answer Key:

(a) 7.54 μH  

 
7. In a transformer, the number of turns in the primary and the secondary are 410 and 1230 respectively. If the current in primary is 6A, then that in the secondary coil is
(a) 2 A 

(b) 18 A
(c) 12 A 

(d) 1 A

Answer Key:

(a) 2 A 

 
8. A step-down transformer reduces the supply voltage from 220 V to 11 V and increase the current from 6 A to 100 A. Then its efficiency is
(a) 1.2 

(b) 0.83
(c) 0.12 

(d) 0.9

Answer Key:

(b) 0.83 

 
9. In an electrical circuit, R, L, C and AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and current in the circuit is $\frac{\mathbf{\pi }}{\mathbf{3}}$. Instead, if C is removed from the circuit, the phase difference is again $\frac{\mathrm{\pi }}{3}$
The power factor of the circuit is  

(a) $\frac{\mathbf{1}}{\mathbf{2}}$

(b) $\frac{\mathbf{1}}{\sqrt{\mathbf{2}}}$
(c) 1 

(d) $\frac{\sqrt{\mathbf{3}}}{\mathbf{3}}$

Answer Key:

(c) 1  

 
10. In a series RL circuit, the resistance and inductive reactance are the same. Then the phase difference between the voltage and current in the circuit is

(a) $\frac{\mathbf{\pi }}{\mathbf{4}}$

(b) $\frac{\mathbf{\pi }}{\mathbf{2}}$
(c) $\frac{\mathbf{\pi }}{\mathbf{6}}$

(d) zero

Answer Key:

(a) $\frac{\mathbf{\pi }}{\mathbf{4}}$ 

 
11. In a series resonant RLC circuit, the voltage across 100 Ω resistor is 40 V. The resonant frequency ω is 250 rad/s. If the value of C is 4 μF, then the voltage across L is
(a) 600 V 

(b) 4000 V
(c) 400V 

(d) 1 V

Answer Key:

(c) 400V  

 
12. An inductor 20 mH, a capacitor 50 μF and a resistor 40 Ω are connected in series across a source of emf V = 10 sin 340 t. The power loss in AC circuit is
(a) 0.76 W 

(b) 0.89 W
(c) 0.46 W 

(d) 0.67 W

Answer Key:

(c) 0.46 W  

 
13. The instantaneous values of alternating current and voltage in a circuit are
$\mathbf{i}\mathbf{=}\frac{\mathbf{1}}{\sqrt{\mathbf{2}}}\mathbf{sin}\mathbf{\left(}\mathbf{100}\mathbf{\pi }\mathbf{t}\mathbf{\right)}\mathbf{A}\mathbf{ }\mathbf{a}\mathbf{n}\mathbf{d}$

$\mathbf{v}\mathbf{=}\frac{\mathbf{1}}{\sqrt{\mathbf{2}}}\mathbf{sin}\mathbf{(}\mathbf{100}\mathbf{\pi }\mathbf{t}\mathbf{+}\frac{\mathbf{\pi }}{\mathbf{3}}\mathbf{)}\mathbf{v}\mathbf{.}$
The average power in watts consumed in the circuit is
(a) $\frac{\mathbf{1}}{\mathbf{4}}$

(b) $\frac{\sqrt{\mathbf{3}}}{\mathbf{4}}$
(c) $\frac{\mathbf{1}}{\mathbf{2}}$

(d) $\frac{\mathbf{1}}{\mathbf{8}}$

Answer Key:

(d) $\frac{\mathbf{1}}{\mathbf{8}}$ 

 
14. In an oscillating LC circuit, the maximum charge on the capacitor is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic fields is
(a) $\frac{\mathrm{Q}}{2}$

(b) $\frac{\mathrm{Q}}{\sqrt{3}}$
(c) $\frac{\mathrm{Q}}{\sqrt{2}}$

(d) Q

Answer Key:

(c) $\frac{\mathrm{Q}}{\sqrt{2}}$ 

15. $\frac{20}{{\mathrm{\pi }}^2}$ inductor is connected to a capacitor of capacitance C. The value of C in order to impart maximum power at 50 Hz is
(a) 50 μF 

(b) 0.5 μF
(c) 500 μF 

(d) 5 μF  

Answer Key:

(d) 5 μF    

 

II. Short answer questions.

12th Physics

III. Long answer questions. 

12th Physics

IV. Exercises.   

12th Physics