12th Physics - Book Back Answers - Unit 8 Dual nature Of Radiation And Matter - English Medium Guides

  

 

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Tamil Nadu Board 12th Standard Physics - Unit 8: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Unit 8 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 8 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 wavelength ${\mathbf{\lambda }}_{\mathbf{e}}$ of an electron and ${\mathbf{\lambda }}_{\mathbf{p}}$ of a photon of same energy E are related by 

a) ${\mathbf{\lambda }}_{\mathbf{p}}\mathbf{\propto }\mathbf{ }{\mathbf{\lambda }}_{\mathbf{e}}$ 

b) ${\mathbf{\lambda }}_{\mathbf{p}}\mathbf{\propto }\sqrt{\mathbf{ }{\mathbf{\lambda }}_{\mathbf{e}}}$  

c) ${\mathbf{\lambda }}_{\mathbf{p}}\mathbf{\propto }\mathbf{ }\frac{\mathbf{1}}{\sqrt{{\mathbf{\lambda }}_{\mathbf{e}}}}$

d) ${\mathbf{\lambda }}_{\mathbf{p}}\mathbf{\propto }\mathbf{ }{{\mathbf{\lambda }}_{\mathbf{e}}}^{\mathbf{2}}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

d) ${\mathbf{\lambda }}_{\mathbf{p}}\mathbf{\propto }\mathbf{ }{{\mathbf{\lambda }}_{\mathbf{e}}}^{\mathbf{2}}$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$

2. In an electron microscope, the electrons are accelerated by a voltage of 14 kV. If the voltage is changed to 224 kV, then the de Broglie wavelength associated with the electrons would
a) increase by 2 times
b) decrease by 2 times
c) decrease by 4 times
d) increase by 4 times

${\mathbf{<b>Answer\; Key: </b>}}^{}$

c) decrease by 4 times${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$ 

3. The wave associated with a moving particle of mass 3 × ${\mathbf{10}}^{\mathbf{-}\mathbf{6}}$ g has the same wavelength as an electron moving with a velocity 6 x ${\mathbf{10}}^{\mathbf{6}}\mathbf{ }\mathbf{m}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$ . The velocity of the particle is
a) 1.82 × ${\mathbf{10}}^{\mathbf{-}\mathbf{18}}\mathbf{ }\mathbf{m}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$
b) 9 × ${\mathbf{10}}^{\mathbf{-}\mathbf{2}}\mathbf{ }\mathbf{m}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$
c) 3 × ${\mathbf{10}}^{\mathbf{-}\mathbf{31}}\mathbf{ }\mathbf{m}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$
d) 1.82 × ${\mathbf{10}}^{\mathbf{-}\mathbf{15}}\mathbf{ }\mathbf{m}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

d) 1.82 × ${\mathbf{10}}^{\mathbf{-}\mathbf{15}}\mathbf{ }\mathbf{m}\mathbf{ }{\mathbf{s}}^{\mathbf{-}\mathbf{1}}$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$${\mathbf{ }}^{}$

4. When a metallic surface is illuminated with radiation of wavelength  , the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2 , the stopping potential is $\frac{\mathbf{V}}{\mathbf{4}}$. The threshold wavelength for the metallic surface is (NEET 2016)
a) 4λ 

b) 5λ
c) $\frac{\mathbf{5}}{\mathbf{2}}$λ
d) 3λ

${\mathbf{<b>Answer\; Key: </b>}}^{}$

d) 3λ${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$ 

5. If a light of wavelength 330 nm is incident on a metal with work function 3.55 eV, the electrons are emitted. Then the wavelength of the wave associated with the emitted electron is (Take h = 6.6 × ${\mathbf{10}}^{\mathbf{-}\mathbf{34}}$Js)
a) <2.75×10${\mathbf{10}}^{\mathbf{-}\mathbf{9}}$m 

b) $\ge 2.75\times {\mathbf{10}}^{\mathbf{-}\mathbf{9}}m$
c) $\le 2.75\times {\mathbf{10}}^{\mathbf{-}\mathbf{12}}m$

d) <2.5×10${\mathbf{10}}^{\mathbf{-}\mathbf{10}}$m

${\mathbf{<b>Answer\; Key: </b>}}^{}$

b) $\ge 2.75\times {\mathbf{10}}^{\mathbf{-}\mathbf{9}}m$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$
6. A photoelectric surface is illuminated successively by monochromatic light of wavelength $\frac{\mathbf{\lambda }}{}$ and $\frac{\mathrm{\lambda }}{2}$ . If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the material is
a) $\frac{\mathbf{h}\mathbf{c}}{\mathbf{\lambda }}$
b) $\frac{\mathbf{2}\mathbf{hc}}{\mathbf{\lambda }}$
c) $\frac{\mathbf{hc}}{\mathbf{3}\mathbf{\lambda }}$
d) $\frac{\mathbf{hc}}{\mathbf{2}\mathbf{\lambda }}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

d) $\frac{\mathbf{hc}}{\mathbf{2}\mathbf{\lambda }}$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$$\frac{\mathbf{ }}{}$
7. In photoelectric emission, a radiation whose frequency is 4 times threshold frequency of a certain metal is incident on the metal. Then the maximum possible velocity of the emitted electron will be
a) $\sqrt{\frac{\mathbf{h}{\mathbf{v}}_{\mathbf{0}}}{\mathbf{m}}}$

b) $\sqrt{\frac{\mathbf{6}\mathbf{h}{\mathbf{v}}_{\mathbf{0}}}{\mathbf{m}}}$
c) $\mathbf{2}\sqrt{\frac{\mathbf{h}{\mathbf{v}}_{\mathbf{0}}}{\mathbf{m}}}$
d) $\sqrt{\frac{\mathbf{h}{\mathbf{v}}_{\mathbf{0}}}{\mathbf{2}\mathbf{m}}}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

b) $\sqrt{\frac{\mathbf{6}\mathbf{h}{\mathbf{v}}_{\mathbf{0}}}{\mathbf{m}}}$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$
8. Two radiations with photon energies 0.9 eV and 3.3 eV respectively are falling on a metallic surface successively. If the work function of the metal is 0.6 eV, then the ratio of maximum speeds of emitted
electrons in the two cases will be
a) 1:4 

b) 1:3
c) 1:1 

d)1:9 

${\mathbf{<b>Answer\; Key: </b>}}^{}$

b) 1:3

 ${\mathbf{<b> </b>}}^{}$

${\mathbf{b)\; 1.02<br>c)\; 1.5 }}^{}$

${\mathbf{d)\; 0.98}}^{}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

${\mathbf{c)\; 1.5 }}^{}$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$
${\mathbf{<b>11.\; The\; threshold\; wavelength\; for\; a\; metal\; surface\; whose\; photoelectric\; work\; function\; is\; 3.313\; eV\; is<br></b>a)\; 4125\AA }}^{}$

${\mathbf{b)\; 3750\AA <br>c)\; 6000\AA }}^{}$

${\mathbf{d)\; 2062.5\AA }}^{}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

${\mathbf{b)\; 3750\AA }}^{}$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$

${\mathbf{b)\; 2.48\; eV<br>c)\; 1.24\; eV }}^{}$

${\mathbf{d)\; 1.16\; eV}}^{}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

${\mathbf{c)\; 1.24\; eV }}^{}$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$
${\mathbf{<b>13.\; Photons\; of\; wavelength\; \lambda \; are\; incident\; on\; a\; metal.\; The\; most\; energetic\; electrons\; ejected\; from\; the\; metal\; are\; bent\; into\; a\; circular\; arc\; of\; radius\; R\; by\; a\; perpendicular\; magnetic\; field\; having\; magnitude\; B.\; The\; work\; function\; of\; the\; metal\; is </b>}}^{}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$${\mathbf{ }}^{}$

${\mathbf{<b>14.\; The\; work\; functions\; for\; metals\; A,\; B\; and\; C\; are\; 1.92\; eV,\; 2.0\; eV\; and\; 5.0\; eV\; respectively.\; The\; metal/metals\; which\; will\; emit\; photoelectrons\; for\; a\; radiation\; of\; wavelength\; 4100\AA \; is/are</b><br>a)\; A\; only<br>b)\; both\; A\; and\; B<br>c)\; all\; these\; metals<br>d)\; none}}^{}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

${\mathbf{b)\; both\; A\; and\; B}}^{}$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$
${\mathbf{<b>15.\; Emission\; of\; electrons\; by\; the\; absorption\; of\; heat\; energy\; is\; called\_\_\_\_\_\_\_\_\_emission.</b><br>a)\; photoelectric<br>b)\; field<br>c)\; thermionic<br>d)\; secondary }}^{}$

${\mathbf{<b>Answer\; Key: </b>}}^{}$

${\mathbf{c)\; thermionic}}^{}$${\mathbf{<b> </b>}}^{}$

${\mathbf{<b> </b>}}^{}$ 

II. Short answer questions.

12th Physics

III. Long answer questions. 

12th Physics

IV. Exercises.   

12th Physics