PHYSICS - Government of Tamil Nadu

PH YSICS

HIGHER SECONDARY SECOND YEAR

VOLUME - II

Revised based on the recommendation of the Textbook Development Committee

Untouchability is a sin Untouchability is a crime Untouchability is inhuman

TAMILNADU TEXTBOOK CORPORATION

COLLEGE ROAD, CHENNAI - 600 006

c Government of Tamilnadu

First edition - 2005

Revised edition - 2007

CHAIRPERSON

Dr. S. GUNASEKARAN

Reader Post Graduate and Research Department of Physics

Pachaiyappa's College, Chennai - 600 030

REVIEWERS

P. SARVAJANA RAJAN

Selection Grade Lecturer in Physics Govt.Arts College Nandanam, Chennai - 600 035

S. RASARASAN

P.G. Assistant in Physics Govt. Hr. Sec. School Kodambakkam, Chennai - 600 024

S. KEMASARI

Selection Grade Lecturer in Physics Queen Mary's College (Autonomous) Chennai - 600 004

Dr. K. MANIMEGALAI

Reader in Physics The Ethiraj College for Women Chennai - 600 008

G. SANKARI

Selection Grade Lecturer in Physics Meenakshi College for Women Kodambakkam, Chennai - 600 024

G. ANBALAGAN

Lecturer in Physics Aringnar Anna Govt. Arts College Villupuram.

AUTHORS

S. PONNUSAMY

Asst. Professor of Physics S.R.M. Engineering College S.R.M. Institute of Science and Technology (Deemed University) Kattankulathur - 603 203

GIRIJA RAMANUJAM

P.G. Assistant in Physics Govt. Girls' Hr. Sec. School Ashok Nagar, Chennai - 600 083

P. LOGANATHAN

P.G. Assistant in Physics Govt. Girls' Hr. Sec. School Tiruchengode - 637 211 Namakkal District

Dr. N. VIJAYAN

Principal Zion Matric Hr. Sec. School Selaiyur Chennai - 600 073

Dr. HEMAMALINI RAJAGOPAL

Senior Scale Lecturer in Physics Queen Mary's College (Autonomous) Chennai - 600 004

Price : Rs.

This book has been prepared by the Directorate of School Education on behalf of the Government of Tamilnadu

This book has been printed on 60 G.S.M paper

Printed by offsetat:

Preface

The most important and crucial stage of school education is the higher secondary level. This is the transition level from a generalised curriculum to a discipline-based curriculum.

In order to pursue their career in basic sciences and professional courses, students take up Physics as one of the subjects. To provide them sufficient background to meet the challenges of academic and professional streams, the Physics textbook for Std. XII has been reformed, updated and designed to include basic information on all topics.

Each chapter starts with an introduction, followed by subject matter. All the topics are presented with clear and concise treatments. The chapters end with solved problems and self evaluation questions.

Understanding the concepts is more important than memorising. Hence it is intended to make the students understand the subject thoroughly so that they can put forth their ideas clearly. In order to make the learning of Physics more interesting, application of concepts in real life situations are presented in this book.

Due importance has been given to develop in the students, experimental and observation skills. Their learning experience would make them to appreciate the role of Physics towards the improvement of our society.

The following are the salient features of the text book.

N The data has been systematically updated. N Figures are neatly presented. N Self-evaluation questions (only samples) are included to sharpen

the reasoning ability of the student.

While preparing for the examination, students should not restrict themselves, only to the questions/problems given in the self evaluation. They must be prepared to answer the questions and problems from the text/syllabus.

? Dr. S. Gunasekaran Chairperson

III

CONTENTS

6. Atomic Physics 7. Dual Nature of Radiation and

Matter and Relativity 8. Nuclear Physics 9. Semiconductor Devices and

their Applications 10. Communication Systems

Appendix Logarithmic and other tables

Page No. 1

56 83

131 198 238 242

IV

6. Atomic Physics

At atmospheric pressure, air and other gases are poor conductors of electricity. This is because, they do not have free charged particles. However, electric current may be passed through a gas if by some mechanism, charged particles are produced in the gas. This can be done in many ways, such as (i) by applying a large potential difference across a gas column at very low pressure and (ii) by allowing X-rays to pass through the gases.

The study of electric discharge through gases gives valuable information regarding the structure of atoms. This has led to the discovery of electrons by J. J. Thomson and later on, to the discovery of X-rays by Roentgen.

6.1 Discharge of electricity through gases at low pressure -

Discovery of electrons A discharge tube is an arrangement to study the

-+

Induction coil

conduction of electricity through

gases. It is a closed, strong glass

C

A

tube of length 50 cm and diameter 4 cm, filled with a gas. Two metal electrodes C and A are fitted inside

P

Fig 6.1 Discharge tube

the tube at the ends as shown in Fig 6.1. The side tube P is connected

to a high vacuum pump and a low pressure gauge. The electrodes C and

A are connected to the secondary of a powerful induction coil, which

maintains a potential difference of 50,000 V. The electrode C connected

to the negative terminal of the induction coil is called the cathode and

the electrode A connected to the positive terminal is called the anode.

When the pressure of the gas inside the discharge tube is reduced by working the vacuum pump, to about 110 mm of Hg, no discharge occurs through the tube. At a pressure of about 100 mm of Hg, the discharge of electricity through the gas begins and irregular streaks of

1

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