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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