12th Physics - Book Back Answers - Unit 5 Electromagnetic Waves - English Medium Guides

  

 

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Tamil Nadu Board 12th Standard Physics - Unit 5: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Unit 5 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 5 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. The dimension of  is

(a) [L ${\mathrm{T}}^{-1}$] 

(b) [${\mathrm{L}}^2{\mathrm{T}}^{-2}$]

(c) [L−1 T] 

(d) [${\mathrm{L}}^{-2}{\mathrm{T}}^2$]

Answer Key:

(b) [${\mathrm{L}}^2{\mathrm{T}}^{-2}$] 

 

2. If the amplitude of the magnetic field is 3 × 10${\mathbf{10}}^{\mathbf{-}\mathbf{6}}$T, then amplitude of the electric field for a electromagnetic waves is

(a) 100 V ${\mathit{m}}^{\mathbf{-}\mathbf{1}}$

(b) 300 V ${\mathit{m}}^{\mathbf{-}\mathbf{1}}$

(c) 600 V ${\mathit{m}}^{\mathbf{-}\mathbf{1}}$

(d) 900 V ${\mathit{m}}^{\mathbf{-}\mathbf{1}}$

Answer Key:

(d) 900 V ${\mathit{m}}^{\mathbf{-}\mathbf{1}}$ 

 
3. Which of the following electromagnetic radiations is used for viewing objects through fog
(a) microwave 

(b) gamma rays
(c) X- rays 

(d) infrared

Answer Key:

(d) infrared 

 
4. Which of the following is false for electromagnetic waves
(a) transverse
(b) non-mechanical waves
(c) longitudinal
(d) produced by accelerating charges

Answer Key:

(c) longitudinal 

 
5. Consider an oscillator which has a charged particle oscillating about its mean position with a frequency of 300 MHz. The wavelength of electromagnetic waves produced by this oscillator is
(a) 1 m 

(b) 10 m
(c) 100 m 

(d) 1000 m

Answer Key:

(a) 1 m  

 
6. The electric and the magnetic fields, associated with an electromagnetic wave, propagating along negative X axis can be represented by
(a) $\overrightarrow{\mathit{E}}\mathbf{=}{\mathit{E}}_{\mathit{o}}\widehat{\mathit{i}} \mathit{a}\mathit{n}\mathit{d}\mathbf{ }\overrightarrow{\mathit{B}}\mathbf{=}{\mathit{B}}_{\mathit{o}}\widehat{\mathit{k}}$
(b) $\overrightarrow{\mathit{E}}\mathbf{=}{\mathit{E}}_{\mathit{o}}\widehat{\mathit{k}} \mathit{a}\mathit{n}\mathit{d}\mathbf{ }\overrightarrow{\mathit{B}}\mathbf{=}{\mathit{B}}_{\mathit{o}}\widehat{\mathit{j}}$

(c) $\overrightarrow{\mathit{E}}\mathbf{=}{\mathit{E}}_{\mathit{o}}\widehat{\mathit{i}} \mathit{a}\mathit{n}\mathit{d}\mathbf{ }\overrightarrow{\mathit{B}}\mathbf{=}{\mathit{B}}_{\mathit{o}}\widehat{\mathit{j}}$
(d) $\overrightarrow{\mathit{E}}\mathbf{=}{\mathit{E}}_{\mathit{o}}\widehat{\mathit{j}} \mathit{a}\mathit{n}\mathit{d}\mathbf{ }\overrightarrow{\mathit{B}}\mathbf{=}{\mathit{B}}_{\mathit{o}}\widehat{\mathit{i}}$

Answer Key:

(b) $\overrightarrow{\mathit{E}}\mathbf{=}{\mathit{E}}_{\mathit{o}}\widehat{\mathit{k}} \mathit{a}\mathit{n}\mathit{d}\mathbf{ }\overrightarrow{\mathit{B}}\mathbf{=}{\mathit{B}}_{\mathit{o}}\widehat{\mathit{j}}$ 

 
7. In an electromagnetic wave travelling in free space the rms value of the electric field is 3 V ${\mathit{m}}^{\mathbf{-}\mathbf{1}}$. The peak value of the magnetic field is
(a) 1.414 × ${10}^{-8}$ T 

(b) 1.0 × ${10}^{-8}$ T
(c) 2.828 × ${10}^{-8}$ T 

(d) 2.0 × ${10}^{-8}$ T

Answer Key:

(a) 1.414 × ${10}^{-8}$ T 

 
8. An e.m. wave is propagating in a medium with a velocity $\overrightarrow{\mathrm{v}}=\mathrm{v}\widehat{\mathrm{i}}$. The instantaneous oscillating electric field of this e.m. wave is along +y-axis, then the direction of oscillating magnetic field of the e.m. wave will be along:
(a) –y direction
(b) –x direction
(c) +z direction
(d) –z direction

Answer Key:

(c) +z direction 

 
9. If the magnetic monopole exists, then which of the Maxwell’s equation to be modified?.
(a) $\underset{\mathbf{s}}{\mathbf{\oint }}\overrightarrow{\mathbf{E}}\mathbf{.}\mathbf{d}\overrightarrow{\mathbf{A}}\mathbf{=}\frac{{\mathbf{Q}}_{\mathbf{e}\mathbf{n}\mathbf{c}\mathbf{l}\mathbf{o}\mathbf{s}\mathbf{e}\mathbf{d}}}{{\mathbf{ϵ}}_{\mathbf{o}}}$
(b) $\underset{\mathbf{s}}{\mathbf{\oint }}\overrightarrow{\mathbf{B}}\mathbf{.}\mathbf{d}\overrightarrow{\mathbf{A}}\mathbf{=}\mathbf{0}$
(c) $\underset{l}{\mathbf{\oint }}\overrightarrow{\mathbf{B}}\mathbf{.}\mathbf{d}\overrightarrow{l}={\mathit{\mu }}_{\mathit{o}}{\mathit{i}}_{\mathit{c}}\mathbf{+}{\mathit{\mu }}_{\mathit{o}}{\mathit{ϵ}}_{\mathit{o}}\frac{\mathit{d}}{\mathit{d}\mathit{t}}\underset{\mathbf{s}}{\mathbf{\oint }}\overrightarrow{\mathbf{E}}\mathbf{.}\mathbf{d}\overrightarrow{\mathbf{A}}$     
(d) $\underset{l}{\mathbf{\oint }}\overrightarrow{\mathbf{B}}\mathbf{.}\mathbf{d}\overrightarrow{l}=\mathbf{-}\frac{\mathit{d}}{\mathit{d}\mathit{t}}{\mathit{\Phi }}_{\mathit{B}}$

Answer Key:

(b) $\underset{\mathbf{s}}{\mathbf{\oint }}\overrightarrow{\mathbf{B}}\mathbf{.}\mathbf{d}\overrightarrow{\mathbf{A}}\mathbf{=}\mathbf{0}$ 

 
10. Fraunhofer lines are an example of _______ spectrum.
(a) line emission 

(b) line absorption
(c) band emission 

(d) band absorption

Answer Key:

(b) line absorption 

 

11. Which of the following is an electromagnetic wave?
(a) α - rays 

(b) β - rays
(c) γ - rays 

(d) all of them

Answer Key:

(c) γ - rays  

12. Which one of them is used to produce a propagating electromagnetic wave?
(a) an accelerating charge
(b) a charge moving with constant velocity

(c) a stationary charge
(d) an uncharged particle

Answer Key:

(a) an accelerating charge 

 
13. If $\mathbf{E}\mathbf{=}{\mathbf{E}}_{\mathbf{o}}\mathbf{ }\mathbf{s}\mathbf{i}\mathbf{n}\mathbf{[}{\mathbf{10}}^{\mathbf{6}}\mathbf{ }\mathbf{x}\mathbf{-}\mathbf{\omega }\mathbf{t}\mathbf{]}$ be the electric field of a plane electromagnetic wave, the value of ω is
(a) 0.3×${\mathbf{10}}^{\mathbf{-}\mathbf{14}}\mathbf{ }\mathbf{r}\mathbf{a}\mathbf{d}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$
(b) 3×${\mathbf{10}}^{\mathbf{-}\mathbf{14}}\mathbf{ }\mathbf{r}\mathbf{a}\mathbf{d}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$
(c) 0.3×${\mathbf{10}}^{\mathbf{-}\mathbf{14}}\mathbf{ }\mathbf{r}\mathbf{a}\mathbf{d}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$
(d) 3×${\mathbf{10}}^{\mathbf{-}\mathbf{14}}\mathbf{ }\mathbf{r}\mathbf{a}\mathbf{d}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$

Answer Key:

(d) 3×${\mathbf{10}}^{\mathbf{-}\mathbf{14}}\mathbf{ }\mathbf{r}\mathbf{a}\mathbf{d}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$

${\mathbf{ }}^{}$ 
14. Which of the following is NOT true for electromagnetic waves?.
(a) it transports energy
(b) it transports momentum
(c) it transports angular momentum
(d) in vacuum, it travels with different speeds which depend on their frequency

Answer Key:

(d) in vacuum, it travels with different speeds which depend on their frequency 

 
15. The electric and magnetic fields of an electromagnetic wave are
(a) in phase and perpendicular to each other
(b) out of phase and not perpendicular to each other
(c) in phase and not perpendicular to each other
(d) out of phase and perpendicular to each other 
Answer Key:

(a) in phase and perpendicular to each other 

  

II. Short answer questions.

12th Physics

III. Long answer questions. 

12th Physics

IV. Exercises.   

12th Physics