physics book Output - DelE Directorate of...

Comprehensive Guidelines

For Academic Excellence

in

Comprehensive Guidelines

For Academic Excellence

in

PHYSICS

for

PGT's

2007

300 Copies, 2007Chief Advisor

Guidance

Rina Ray

Prof. N. K. Sehgal

Dr. Charu Varma

Mr.C.B. Verma

Mr. Sher Singh . . .

Mr. Giri Bhardwaj e

Ms. Sneh Lata . . ., . . . . .,

Ms. Sukhda . . ., . . . .,

Dr. Santosh Verma . . .,

,

Reader Physics, Hansraj College, DU.

Lecturer (Science), PSTE, DIET Pitampura

Retd. Principal

H O D , Physics

Navyug School, Lodhi Road.

D.T.E.A., Sr.S.S., Laxmi Bai Nagar.

Science Counsellor, Pitampura Sci nce Center.

P G T Physics, G G S S S No. 1 Tilak Nagar.

P G T Physics, G S K V B-3 Paschim Vihar.

P G T Physics, G.S.V. Rani Bagh.

Secretary, (Education) GNCT of DelhiChairperson, SCERT

Sh. B.N. BajpaiDr. Pratibha Sharma

Course Directors

Material Development Team

Power Point Development Team

Dr. Charu VarmaMr M.M. Roy

Lecturer (Science),PSTE, DIET Pitampura.Lecturer, DRU, DIET Ghumanhera.

Mr. R. Ranga Rajan . . .

Mr. Rakesh Bhardwaj . . .

Prof. N. K. Sehgal

Mr. Sher Singh . . .

Mr. R. Ranga Rajan . . .,

Mr. Rakesh Bhardwaj . . .

H O D , Physics

H O D , Physics

M.A.P.S., Pitampura, Delhi

Reader Physics, Hansraj College, DU.

H O D , Physics

Navyug School, Lodhi Road.

H O D Physics

D.T.E.A., Sr.S.S., Laxmi Bai Nagar.

H O D , Physics

M.A.P.S., Pitampura, Delhi

Educational Stores, 1/1978, Modern Shahdara, Shahdara, Delhi-110032

Published by Mukesh Yadav, Publication officer, State Council of Educational Research & Training, New Delhi on

behalf of SCERT and printed at

(ii)

Quality education has always been a major concern for the educationalists. Inthe advent of Globalization, Liberalization and Economic Reforms, there is aconstant need to restructure the system and make it more flexible and pragmaticand in tune with changing manpower requirements. To keep pace with thechanging scenario, NCERT and CBSE have brought in required changes in theschool curriculum and learners' assessments at all levels. There is a need to orientour teachers about these changes in the textbooks and the latest - technologies foreffective implementation in the teaching learning processes.

Teachers' Manual developed by SCERT and DIET Faculty in differentsubjects at Senior Secondary level is an attempt to meet this objective. TheManuals are based as per the needs of the teachers which include grey areas andhard spots in different subjects meant for quality improvement. The objective isalso to make the teaching learning process interactive and enabling students tomove beyond the textbooks, which is one of the concerns of National CurriculumFramework-2005. It will also give an insight to teachers about different activities,projects, assignments, case- studies, application based questions on new CBSEpattern to develop critical thinking and problem solving abilities. These manualshave been developed through workshop mode incorporating the feedback byteachers on new textbooks by NCERT.

There have been remarkable developments in the Government School resultsof classes X and XII. The results of class X have gone up by 29% in last two years.In Science, the result of objective type questions (MCQ) was 100%, which iscommendable. The aggregate result of class XII (after compartment) is competingwith the results of public schools, which is phenomenal. The credit goes to variousinitiatives taken by Directorate of Education, SCERT/DIET for qualityimprovement in Government Schools of Delhi. This has also been possible due tothe intensive training in content and methodology in the recent past and by thecontinuous monitoring and follow -up by the officials at all levels.

I acknowledge a deep sense of gratitude to the team of Advisors and Expertswho have provided their valuable suggestions in preparing these Manuals andthanks are also extended to the Editors, Co-ordinators, team of subject experts, allSCERT/DIET faculty (academic and administration), publication-division whohave immensely contributed in completing this assignment.

Preface...

(iii)

subject experts, all SCERT/DIET faculty (academic and administration),publication-division who have immensely contributed in completing thisassignment.

I sincerely hope that these Teachers' Manuals will enable our teachers to makethe class room processes more interactive and activity-based for enhancement ofoverall performance of children in Government Schools.

Your suggestions and comments regarding the Teachers' Manual arewelcome.

B.N Bajpai(Director)SCERT, Varun Marg,Defence ColonyNew Delhi

(iv)

CONTENTS Page No.

b. Sovled Sample Papers with Marking Scheme

(v)

1

9

10-34

35-69

74-75

76-78

79-80

81-85

86-87

88-89

70-73

2

2-5

6-8

CHAPTER-1

C.B.S.E SYLLABUS

PHYSICS (Code No. 042)

Senior Secondary stage of school education is a stage of transition from general education to

discipline-based focus on curriculum. The present updated syllabus keeps in view the rigour and depth

of disciplinary approach as well as the comprehension level of learners. Due care has also been taken

that the syllabus is not heavy and is at the same time, comparable to the international standards. Salient

features of the syllabus include:

• Emphasis on basic conceptual understanding of the content

• Emphasis on use of SI units, symbols, nomenclature of physical quantities and

formulations as per international standards.

• Providing logical sequencing of units of the subject matter and proper placement ofconcepts with their linkage for better learning.

• Reducing the curriculum load by eliminating overlapping of concepts/ content with in thediscipline and other disciplines.

• Promotion of process-skills, problem-solving abilities and applications of Physicsconcepts.

Besides, the syllabus also attempts to

• strengthen the concepts developed at the secondary stage to provide firm

foundation for further learning in the subject.

• expose the learners to different processes used in Physics-related industrialand technological applications.

• develop process-skills and experimental, observational, manipulative,decision making and investigatory skills in the learners.

• promote problem solving abilities and creative thinking in learners.

• develop conceptual competence in the learners and make them realize andappreciate the interface of Physics with other disciplines.

(1)

COURSE STRUCTURE

Class XII - Theory

One Paper Time: 3 Hours 70 Marks

Total 70

Unit I: Electrostatics (Periods 25)

Unit I Electrostatics 08

Unit II Current Electricity 07

Unit III Magnetic effect of current & Magnetism 08

Unit IV Electromagnetic Induction andAlternating current 08

Unit V Electromagnetic Waves 03

Unit VI Optics 14

Unit VII Dual Nature of Matter 04

Unit VIII Atoms and Nuclei 06

Unit IX Electronic Devices 07

Unit X Communication Systems 05

• Electric Charges; Conservation of charge, Coulomb's law-force between two point charges,

forces between multiple charges; superposition principle and continuous charge distribution.

Electric field, electric field due to a point charge, electric field lines; electric dipole, electric field

due to a dipole; torque on a dipole in uniform electric field. Electric flux, statement of Gauss's

theorem and its applications to find field due to infinitely long straight wire, uniformly charged

infinite plane sheet and uniformly charged thin spherical shell (field inside and outside). Electric

potential, potential difference, electric potential due to a point charge, a dipole and system of

charges; equipotential surfaces, electrical potential energy of a system of two point charges and of

electric dipole in an electrostatic field. Conductors and insulators, free charges and bound charges

inside a conductor. Dielectrics and electric polarisation, capacitors and

(2)

capacitance, combination of capacitors in series and in parallel, capacitance of a parallel plate capacitor

with and without dielectric medium between the plates, energy stored in a capacitor. Van de Graaff

generator.

Electric current, flow of electric charges in a metallic conductor, drift velocity, mobility and their

relation with electric current; Ohm's law, electrical resistance, V-I characteristics(linear and

non-linear), electrical energy and power, electrical resistivity and conductivity. Carbon resistors,

colour code for carbon resistors; series and parallel combinations of resistors; temperature

dependence of resistance.

Internal resistance of a cell, potential difference and emf of a cell, combination of cells in series

and in parallel. Kirchhoff's laws and simple applications. Wheatstone bridge, metre bridge.

Potentiometer - principle and its applications to measure potential difference and for comparing

emf of two cells; measurement of internal resistance of a cell.

Concept of magnetic field, Oersted's experiment. Biot - Savart law and its application to current

carrying circular loop. Ampere's law and its applications to infinitely long straight wire, straight

and toroidal solenoids. Force on a moving charge in uniform magnetic and electric fields.

Cyclotron. Force on a current-carrying conductor in a uniform magnetic field. Force between two

parallel current-carrying conductors-definition of ampere. Torque experienced by a current loop

in uniform magnetic field; moving coil galvanometer-its current sensitivity and conversion to

ammeter and voltmeter. Current loop as a magnetic dipole and its magnetic dipole moment.

Magnetic dipole moment of a revolving electron. Magnetic field intensity due to a magnetic

dipole (bar magnet) along its axis and perpendicular to its axis. Torque on a magnetic dipole (bar

magnet) in a uniform magnetic field; bar magnet as an equivalent solenoid, magnetic field lines;

Earth'smagnetic field and magnetic elements.

Unit II: Current Electricity (Periods 22)

Unit III: Magnetic Effects of Current and Magnetism (Periods 25)

•

•

(3)

Unit IV: Electromagnetic Induction andAlternating Currents (Periods 20)

Unit V: Electromagnetic waves (Periods 4)

Unit VI: Optics (Periods 30)

•

•

•

Electromagnetic induction; Faraday's law, induced emf and current; Lenz's Law, Eddy currents.

Self and mutual inductance. Need for displacement current.

Alternating currents, peak and rms value of alternating current/voltage; reactance and

impedance; LC oscillations (qualitative treatment only), LCR series circuit, resonance; power in

AC circuits, wattless current.AC generator and transformer.

Electromagnetic waves and their characteristics (qualitative ideas only). Transverse nature of

electromagnetic waves. Electromagnetic spectrum (radio waves, microwaves, infrared, visible,

ultraviolet, Xrays, gamma rays) including elementary facts about their uses.

Reflection of light, spherical mirrors, mirror formula. Refraction of light, total internal reflection

and its applications, optical fibres, refraction at spherical surfaces, lenses, thin lens formula, lens-

maker's formula. Magnification, power of a lens, combination of thin lenses in contact.

Refraction and dispersion of light through a prism. Scattering of light - blue colour of the sky and

reddish appearance of the sun at sunrise and sunset. Optical instruments: Human eye, image

formation and accommodation, correction of eye defects (myopia, hypermetropia, presbyopia

and astigmatism) using lenses. Microscopes and astronomical telescopes (reflecting and

refracting) and their magnifying powers. Wave optics: wave front and Huygens' principle,

reflection and refraction of plane wave at a plane surface using wave fronts. Proof of laws of

reflection and refraction using Huygens' principle. Interference, Young's double slit experiment

and expression for fringe width, coherent sources and sustained interference of light. Diffraction

due to a single slit, width ofcentral maximum. Resolving power

of microscopes and astronomical telescopes. Polarisation, plane polarised light; Brewster's law,

uses of plane polarised light and Polaroids.

(4)

Unit VII: Dual Nature of Matter and Radiation (Periods 8)

Unit VIII:Atoms & Nuclei (Periods 18)

Unit IX: Electronic Devices (Periods 18)

Unit X: Communication Systems (Periods 10)

•

•

•

•

Dual nature of radiation. Photoelectric effect, Hertz and Lenard's observations; Einstein's

photoelectric equation-particle nature of light. Matter waves-wave nature of particles, de Broglie

relation. Davisson-Germer experiment.

Alpha-particle scattering experiment; Rutherford's model of atom; Bohr model, energy levels,

hydrogen spectrum. Composition and size of nucleus, atomic masses, isotopes, isobars; isotones.

Radioactivityalpha, beta and gamma particles/rays and their properties; radioactive decay law.

Mass-energy relation, mass defect; binding energy per nucleon and its variation with mass

number; nuclear fission and fusion.

Semiconductors; semiconductor diode I-V characteristics in forward and reverse bias,diode as a

rectifier; I-V characteristics of LED, photodiode, solar cell, and Zener diode;Zener diode as a

voltage regulator. Junction transistor, transistor action, characteristics of a transistor; transistor as

an amplifier (common emitter configuration) and oscillator. Logic gates (OR, AND, NOT,

NAND and NOR). Transistor as a switch.

Elements of a communication system (block diagram only); bandwidth of signals (speech, TV

and digital data); bandwidth of transmission medium. Propagation of electromagnetic waves

in the atmosphere, sky and space wave propagation. Need for modulation. Production and

detection of an amplitude-modulated wave.

(5)

CLASS XII - PRACTICALS

Every student will perform 10 experiments (5 from each section) & 8 activities (4 from each section)

during the academic year.

One experiment from any one section 8 Marks

Two activities (one from each section) (4+4) 8 Marks

Practical record (experiments & activities) 6 Marks

Viva on experiments & activities 5 Marks

1. To determine resistance per cm of a given wire by plotting a graph of potential difference versus

current.

2. To find resistance of a given wire using metre bridge and hence determine the specific resistance

of its material.

3. To verify the laws of combination (series/parallel) of resistances using a metre bridge.

4. To compare the emf of two given primary cells using potentiometer.

5. To determine the internal resistance of given primary cell using potentiometer.

6. To determine resistance of a galvanometer by half-deflection method and to find its figure of

merit.

7. To convert the given galvanometer (of known resistance and figure of merit) into an ammeter and

voltmeter of desired range and to verify the same.

8. To find the frequency of the a.c. mains with a sonometer.

Two demonstration experiments must be performed by the teacher with

participation of students. The students will maintain a record of these demonstration experiments.

B. Evaluation Scheme for Practical Examination:

Record of demonstration experiments & Viva based on these experiments 3 Marks

Total 30 Marks

•

•

•

•

•

SECTION A

Experiments

(6)

Activities

1. To measure the resistance and impedance of an inductor with or without iron core.

2. To measure resistance, voltage (AC/DC), current (AC) and check continuity of a given circuit

using multimeter.

3. To assemble a household circuit comprising three bulbs, three (on/off) switches, a fuse and a

power source.

4. To assemble the components of a given electrical circuit.

5. To study the variation in potential drop with length of a wire for a steady current.

6. To draw the diagram of a given open circuit comprising at least a battery, resistor/rheostat, key,

ammeter and voltmeter. Mark the components that are not connected in proper order and correct

the circuit and also the circuit diagram.

4. To find the focal length of a concave lens, using a convex lens.

5. To determine angle of minimum deviation for a given prism by plotting a graph between angle of

incidence and angle of deviation.

6. To determine refractive index of a glass slab using a travelling microscope.

7. To find refractive index of a liquid by using (i) concave mirror, (ii) convex lens and plane mirror.

8. To draw the I-V characteristic curve of a p-n junction in forward bias and reverse bias.

9. To draw the characteristic curve of a zener diode and to determine its reverse break down voltage.

10. To study the characteristics of a common - emitter npn or pnp transistor and to find out the values

of current and voltage gains.

SECTION B

Experiments

1. To find the value of v for different values of u in case of a concave mirror and to find the focal

length.

2. To find the focal length of a convex lens by plotting graphs between u and v or between l/u and l/v.

3. To find the focal length of a convex mirror, using a convex lens.

(7)

Activities

1. To study effect of intensity of light (by varying distance of the source) on an L.D.R.

2. To identify a diode, an LED, a transistor, and IC, a resistor and a capacitor from mixed collection

of such items.

3. Use of multimeter to (i) identify base of transistor. (ii) distinguish between npn and pnp type

transistors. (iii) see the unidirectional flow of current in case of a diode and an LED. (iv) check

whether a given electronic component (e.g. diode, transistor or I C) is in working order.

4. To observe refraction and lateral deviation of a beam of light incident obliquely on a glass slab.

5. To observe polarization of light using two Polaroids.

6. To observe diffraction of light due to a thin slit.

7. To study the nature and size of the image formed by (i) convex lens (ii) concave mirror, on a

screen by using a candle and a screen (for different distances of the candle from the lens/mirror).

8. To obtain a lens combination with the specified focal length by using two lenses from the given

set of lenses.

(8)

(9)

CHAPTER - 2

CHAPTER - 3 a

Unsolved Sample Papers

(10)

29

(24)

CHAPTER - 3 b

Solved Sample Papers withMarking Scheme

(35)

CHAPTER-4

LIST OF LAB APPRATUS AND INSTRUMENTS NEEDED BY THE

STUDENTS ( XI & XII)

(a.) Non Consumable

•

• S

•

•

•

Meter scale and half meter scale

pherical and Cylindrical Body

Beaker

Vernier Calliper

Screw gauge

• Spherical surface-mirror (convex and concave)

• Physical balance

• Parallogram Law of vectors apparatus (Grave's sand apparatus)

• Spherical bob

• Stop clock

• Iron stand

• Apparatus for experiment on friction ( Horizontal and Inclined Plane)

• Burette

• Thermometer

• Measuring tape

• Spherical balls

• Young's modulus apparatus

• Helical spring

• Co-efficient of viscosity apparatus

• Calorimeter

• Sonometer

• Tuning fork

• Resonance tube apparatus

• Fortin's barometer

• Bi-metallic strips.

• Microscope (Travelling)

(70)

(71)

••••••••• a••••••••••

•

•

•

•

•

•

•

•

•

•

•

•

•

•

Black body

Different Masses

Wooden blocks

Dry cells

Battery eliminator

Accumulator

D.C. Ammeter

D.C. Voltmeter

D.C. G lvanometer

Rheostat

Resist nce box

Single Plug Key

Two way Plug Key

Resist nce coil

Meter bridge

Post Office Box

Leclanche cell

Daniel cell

Potentiometer

Inductor

A.C. Voltmeter

A. C. ammet r

Multimeter

Optical ench

Concave Mirror

Convex Mirror

Convex

Convace

Glass prism

Glass slab

a

a

e

B

Lens

Lens

Concave Lens

Convex Lens

Glass slab

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

Drawing board

p-n junction diode

Tra sistor npn and pnp

Re ist rs of high resistance

Integrated circu t

Capacitor

Choke coil

Polaroids

Screen

Bar pendulum

LASER

Photo transistor

Telescope

Electric lamps of different powers

Rubber pads

Bar magnet

Slinky

Plane Mirror

Fuse

Electrically maintained tu fork

Compass needle

Magnifying glass

Logic gates

Complete list of apparatus is also available in science branch.

n

s o

i

ning

Note :

(72)

(b.) Consumable Items

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

Awl

u

c

White paper

Capillary tube

pins

Insulating wire

Iron filing

Switches

Cut outs

Gum

Dusters

Ammonium Chloride

Copper Sulphate

Sodium Chloride

Sulph ric Acid

Sand Paper

Glycerine

Hydro hloric Acid

Thread

Candle

Match box

Connecting wire

(73)

CHAPTER-5

TEN COMMANDMENTS FOR STUDENTSTO SCORE GOOD MARKS IN CLASS XII

1. Identify the areas of your interest and having previous knowledge and study these topics 100%without leaving any pot-holes.

2. Prepare the chapters having more weight age of the areas of your interest and previous knowledgefirst and do them with an eye on a 5 mark question.

3. Instead of leaving the topics like E.M.Waves, Principles of Communication understand toexpress all definitions, interpretation of figures, Advantages and disadvantages of variousdevices andApplications etc.

4. Do the super hit questions/topics like Cyclotron, A.C.Generator, Young's experiment, Gauss'stheorem, Wheatstone's bridge, potentiometer etc.., many times before the examination, so thatyou do not flop during the examination because of the tilted nature of a question.

)

5. Do all the worked examples and the graphs with their Interpretation from NCERT during yourpreparation.

6. Go to the examination hall with a positive frame of mind - particularly on the Physicsexamination day, at least half an hour before without any books and please do not discuss anyquestion with anyone in this period.

7. Start the answer script with the best known question and go in an order-ascending or descendingand do the best known questions and then come on the second round doing the rest of thequestions. Be precise with your answer.

(See attached List of 15 topics

8. In case you are not having good Interpretation skill, try to develop the same. If you are stilldoubtful, first do the best known five mark questions and try to create a good impression in theminds of the paper checker.

9. When you approach the numerical question always understand the question, recall the knownconcept of the question and never try to list the formula and substitute the values. The first linethat you write is always an important one as it is to send the signal to the examiner. Soconceptualize the problem, success will be yours.

10. Present the paper neatly and legibly without cutting and leaving space for anything that you planto do later, since there will not be any time to do later. If you happen to cut, do it neatly such thatthe cut and the un-cut portions are distinguishable. Thinking and formatting the answer beforewriting will improve you on this front. Never leave any question. Write something of what youknow of the answer.

Remember “What you think is wrong may be the correct answer” many a times.

(74)

List of some Super hit topics:

1. CE Transistor amplifier and Oscillator

2. A.C.Generator

3. Transformer

4. Cyclotron

5. Potentiometer

6. Wheatstone's Bridge

7. Young's Experiment

8. Components of Earth's field

9. Application of E.M.Waves

10. Moving coil Galvanometer

11. Photo-electric effect

12. Bohr's Model

13. Modulation and Demodulation with need, advantages and disadvantages with relevant circuits

14. Brewster's Law and Condition for I dark in Diffraction pattern

15. Gauss's theorem - proof and major application on Spherical and line of charges

(75)

CHAPTER- 6

CHALLENGES IN LEARNING

PHYSICS CONCEPTS AND PEDAGOGICAL TIPS

Great men have said that all minds are packed with similar contents. But they work differently based on

the way one tries to use. A systematic approach places everyone on a better platform in academics with

the explosion of knowledge. Learning Obstacles do appear in every learning situation- Major

contribution is from sciences - in particular physics. Even though it is relative --Challenges do exist. With

experience in teaching, one could identify some of the areas in physics where student have a fear or

psychological discomfort.

Some of the identified challenges are listed below :

1. Concept of Gauss's Theorem.

2. Force on a Charge in a Magnetic field

3. Finding the direction of Induced current

4. Study ofAmplifiers in CE- Configuration

To find electric field using Gauss Theorem.

(i) Unable to construct a Gaussian surface

(ii) Finding effective Gaussian area

(iii) Checking for charge enclosed.

(i) Gaussian surface is always symmetrical.

(ii) Even if unsymmetrical is made, the area where the field is perpendicular to the

surface has to be accounted for.

(iii) If only field lines pass through the surface and no charge is enclosed the net flux has

to be zero.

(iv) Flux being a scalar, the net flux is the sum of flux due to all the surfaces involved.

1. Concept of Gauss's Theorem:-

Aim :

Problem :

Solution : As per the course XII requirement,

(76)

2.

Aim :

Problem :

Solution :

3.

Problem :

Force on a charge in a magnetic field.

Identifying the direction of Induced current

Identifying force direction

(i) Sense of directional representation

(ii) Unable to identify the differences due to the nature of charges.

(i) During conceptualization, one should understand that the rules are always framed for

the positive charge motion.

(ii) Fleming's rule is used only when the field and the motion are perpendicular to each

other.

(iii) It may be practiced that one can better turn the note book rather than the hand to arrive

at result i.e. force direction.

Unable to identify the direction of induced current

Solution :

if

then

4.

Problem :

Solution :

(i) Express the Fleming's Right hand rule the way it has to be. Students generally associate

the three fingers with the three quantities Magnetic field, Motion of conductor and the

Induced current direction. It should be noted that the fore finger indicates the magnetic

field and the thumb indicates the direction of the motion of the conductor the

middle finger points the direction of Induced current.

(ii) Recall that the rule is applicable for only perpendicular direction of the Magnetic Field

and motion of the conductor.

(iii) Recall that there needs to be a closed path available for the current to flow. If the closed

path exists completely inside the magnetic field, there may be no current but emf may be

produced.

(iv) It must again and again impress upon that there may be constant field or flux but for

induced emf the field or flux has to change.

Unable to draw a circuit diagram and explain the process of Amplification.

(i) Draw the Transistor with indication of npn or pnp.

(ii) Give Bias for the input and Output side Emitter should be forward biased and

Collector has to be reverse biased.

Study ofAmplifiers in Common- Emitter Configuration

(77)

(iii) Recall that to keep forward bias in the emitter, the signal for amplification has to have amplitude

less than the bias potential.

(iv) Show all these three in the circuit and indicate the direction of current and establish the

conservation of current.

(a) No signal exists

(b) Forward cycle is fed in and

(c) Reverse cycle is applied as input along with the bias potential.

(v ) Try to appreciate the fact that the output with zero signal when adds to addition of forward/

reverse cycle signal there will be increased amplitude.

(vii) Recall as Forward bias increases, increases causing V to decrease and vice-versa causing a

180 phase difference between the output and input.

Like these analysis, the teacher may think, prepare some tips and try to simplify the topics without losing

technicality. Teacher preparedness is tested by every child, when a brilliant question is posed in the class

room. A patient listening to the problems of the child, at least five minutes of mind set for each session

and a goal set for the year, may keep the teacher at better level and the taught will overcome the word

“Challenge and Hard” with positive outlook. Teacher is expected to approach every area conceptually

and device simple steps for the child to follow rather than arriving at the answers to the questions. This

will bring a totally refined approach to teaching learning process and no doubt ignited minds will be

grown in our class-rooms.

I = I + I

I

e c b

c

(v) Write the Kirchoff's rule for the output side V = V - I R and try to explain what happens when

i

ce cc c c

cc

o

(78)

CHAPTER-7

TIPS TO SOLVE NUMERICAL QUESTIONS

Out of all the most ways by which a taught is tested by a teacher the most dreaded is with Numerical

Problems in physics. Due to some teachers, the taught is in the impression that numerical solving alone

can take him to good heights in academics. The fact remains hidden that CBSE class XII physics paper

will have numerical problems worth only. This is again specified only in the guidelines of

2007 sample papers physics XII. The very argument here is not to avoid them but to strengthen your-self

to do the numerical problems with ease and develop a systematic approach to solve them. Text book

reading habit is somehow lost by the children of Delhi and it should be the prime task for all concerned to

bring this habit to the minds of the pupil. If ample opportunity is given to the mind to conceptualize a

given topic, it will solve any problem under the mastered topic. So a systematic approach is expected to

solve numerical. Before a child begins to solve numerical problems, he / she should have read,

comprehended, conceptualized and be prepared mentally to face the variations in any parameter. Merely

memorizing the formula and trying to substitute the values will not solve the problem and this practice

should be stop and discouraged.

Let us take some examples in solving numerical problems and see how the change in approach removes

the problem faced:

In potentiometer based questions, the following steps lead to clear understanding and correct

results:-

A. Draw the circuit diagram from the information given in the question.

B. In the Primary Circuit

(i) Find the current through potentiometer wire.

(ii) Find potential difference across the potentiometer wire

(iii) Find potential gradient V = V/Lwhere Lis the length of the potentiometer wire.

C. Using the Secondary circuit

(iv) Try to find the balancing for an emf or terminal voltage of the cell in the secondary circuit using

potential gradient (V .) i.e. V . X = V or E

(v) V or E has to be chosen or found based on whether any shunt resistor exists or not.

15 marks

1.

Student should be advised to use the concepts rather than apply the formula.

Potentiometer related questions:-

.

g

g g

(79)

CHAPTER-8

POINTS TO PONDER (NCERT CLASS XII TEXTBOOK)

1.Electric Charges and Fields

2.Electrostatic Potential and Capacitance

Point 6 :

Point 8 :

Point 4 :

Point 7 :

NCERT

Velocity of a body is different in different frames of reference and so does the kinetic energy.

Kinetic energy is also depends on the mass which differs with the velocity of the particle when it

is comparable to the speed of light. Charge is a scalar and is not a frame dependent quantity.

Quantisation of charge as a phenomena is supported with the Millikan's oil drop experiment. So it

can be a law of nature. However, when the existence of the particles like Quark is established

there will be a drop in the scale of quantization to 1/3 of the charge on electron.

Slight deviation of the dipole from the electric field can bring a restoring torque and as a result

there can be a S.H.M. The restoring torque can be 2 l xq E Sin and can be equated to Time

period can be easily found from the relation �The oscillation will be a damped only

when� there is presence of dissipative forces.

A cavity is free from Electric field even if there are charges on the surface of a conductor.

However if there is a charge placed inside the cavity, it will create a field in all its surroundings extending

to infinity. This is established from the approach of spherical symmetry discussed in the text

book. So electrostatic shielding is not possible with a charge inside the cavity.

rd

[- ��

2 � I2 l q E

(81)

3.Current Electricity

4. Moving Charges and Magnetism

Point 1 :

Point 6:

Point 1 :

The current flowing in a conductor is given by the integral j. ds So even if a uniform

conductor is considered the current density is taken a constant over a smaller element and the

current can be found. Both the density and area are vectors satisfying the law of vector addition

and only the component of j in line with the area vector or normal to the area contribute to the

current.

The shape of the circuit in any way does not influence the flowing current. The conservation of

charge is obeyed in whatsoever way one bends the loop. Quite often students take into different

values of resistance and thereby current when a wire is bend into a square or a circle and the

equivalent resistance is found between the diagonally opposite ends.

One of the remarkable difference between the electric and the magnetic field is that the magnetic

field lines form closed path and the electric field lines do not. The direction of field between the

poles of a magnet is from the south to North in line with the field while in a electric dipole the field

is from the +ve charge to the -ve charge.

� �

Point 3 :

Point 7 :

The Lorentz force will signify only the electric force if the frame of reference is having a velocity

and in its reference the charge is at rest. The very motion of the charge is to be defined with the

presence of an electric field. This is the second indication for the student to understand that there

exists a link between the electric and magnetic field. [ The first link is in the continuity developed

between the plates of a capacitor due to the changing electric field causing a magnetic effect.]

The phenomena of Hysteresis is a control on human by nature. It is the study of the inability to

retrace the same path while magnetizing and Demagnetizing. In the making of a magnet one does

work and align the dipoles in an order. Similarly demagnetizing is also a orderly disorderliness

expecting man to do work. The Domain theory of Ferromagnetism explains the formation of the

Hysteresis loop. The area covered by the Hysteresis is a measure of the energy used for unit

volume of the material per cycle of magnetization and demagnetization.

5. Magnetism and Matter

(82)

Point 8 :

Point 3 :

Diamagnetism is a universal property. Superconductors expel magnetic field [Meissner Effect] as

do the Diamagnets. So every material is said to exhibit this property at one temperature or

another.

Induced emf is possible when there is a variation in area, field and/or the orientation of the area

with the field. So when there is a moving charge in a fixed field or a varying field in a static charge

there will be induced emf.

6. Electromagnetic Induction

Point 3

Point 7 :

Point 8 :

:

The Lorentz force will signify only the electric force if the frame of reference is having a velocity

and in its reference the charge is at rest. The very motion of the charge is to be defined with the

presence of an electric field. This is the second indication for the student to understand that there

exists a link between the electric and magnetic field. [ The first link is in the continuity developed

between the plates of a capacitor due to the changing electric field causing a magnetic effect.]

The phenomena of Hysteresis is a control on human by nature. It is the study of the inability to

retrace the same path while magnetizing and Demagnetizing. In the making of a magnet one does

work and align the dipoles in an order. Similarly demagnetizing is also a orderly disorderliness

expecting man to do work. The Domain theory of Ferromagnetism explains the formation of the

Hysteresis loop. The area covered by the Hysteresis is a measure of the energy used for unit

volume of the material per cycle of magnetization and demagnetization.

Diamagnetism is a universal property. Superconductors expel magnetic field [Meissner Effect] as

do the Diamagnets. So every material is said to exhibit this property at one temperature or

another.

5. Magnetism and Matter

6. Electromagnetic Induction

(83)

Point 4 :

Point 5 :

Point 9 :

The eddy current formed in the plate creates a magnetic field which is opposed by the applied

magnetic field [ Lenz's explanation ]. So there is a damping effect on the disc made to oscillate in

the presence of a magnetic field.

In an a.c. network having an inductor, a capacitor and a resistor in series the net potential applied

is given by the relation where the symbols carry the usual meaning. This is

because of the phase difference that exists between the voltage and the current. The same reason

holds when current conservation is to be established with a Capacitor and an Inductor in parallel.

The current drawn from a source is given by the relation

The average power consumed by the ac circuit is given by the relation where

is the phase difference between the voltage and the current. Since the value of Cos is to be less

than 1 this value decides the proportion of maximum power that will be consumed in the ac

circuit. It is given by the ratio of the Resistance to the Impedance of the circuit.

7.Alternating Current

V= (V - V ) + V

Similar to what has been explained in this point we can observe as we place a screen

perpendicularly along the axis of a convex lens receiving white light. Since the lens medium

offers different refractive index for different constituent colours the (same) lens offers different

focal length. On the screen one can observe coloured rings with violet at the centre and red at the

extreme - close to the lens and as one moves the screen away there will be a position with red

colour as the centre and violet as the outer ring.

It may added to the point 1 that Huygen was not able explain

(i) Why the energy released by any Wavefront goes only in the forward direction?

(ii) Is light a transverse or a Longitudinal wave?

The spark created by Huygen has made Young, Fresnel and Fraunhofer to explain various

phenomena associated with light. The first question was answered byYoung. The intensity

with �as the phase difference will become zero for the backward direction. The

second question was answered by the Polarization experiment establishing the Transverse nature

of light.

L C R

2 2

9. Ray Optics and Optical Instruments

10. Wave Optics

Point 2 :

Point 1:

P = I V Cos

I=2a ( 1+Cos )

av rms rms �

� �

� � �2

I=I -IC L

(84)

Point 4:

'D' 'a'

Point 4:

Point 5 :

14. Semiconductor Electronics; Materials, Devices and Simple Circuits

The limit of application of Ray optics was established by Fresnel's distance. As the divergence of

the light over a distance exceeds the slit width then wave optics has to be applied. The

distance D with such a spread called Fresnel distance D The angular width for this

distance is a and corresponds to the first minima of the diffraction pattern and also the clear

resolution limit for telescopes.

The shift from particle to wave was challenged by the Photo-electric effect which made mankind

to consider energy as a packet with energy equivalent and indirectly established the dual

nature of matter later supported by the Davisson and Germer experiment.

The dual nature also showed difference between the Classical and Modern Physics in

distinguishing the effects of Intensity variation and Frequency variation.As you may recall that

(i) minimum frequency is required for Photo-electric emission to take plac even though the Intensity

is increased

(ii) the stopping potential is measured with the frequency rather than the Intensity.

� a /

For a transistor to work the way it is expected [as from its name] to work the following points are

to be kept in mind.

(i) The emitter is to be densely doped

(ii) The base region should be lightly doped and thin

(iii) The collector region is to be moderately doped

(i) The emitter should be forward biased

(ii) The Collector is to be reverse biased.

This will make the transistor to perform its task of transferring Majority carriers from low

resistance region [emitter] to the high resistance region [collector].

2

� �

11. Dual Nature of Radiation and Matter

hν

Point 3:

While using a transistor in a circuit

(85)

CHAPTER-9

SUGGESTIONS TO IMPROVE THE COMMON ERRORSCOMMITTED BY STUDENTS IN EXAMS

1. The teachers should tell the students about the possible distribution of marks over the different value

points (or different requirements) specially for a long answer question. For example distribution of 5

marks in a descriptive type question may be distributed over different aspects such as diagram,

labelling, description, derivation, formulas, properties, limitation, precautions, application etc.

whatever may be, depending on the question.

2. If the answer is suported by a diagram, then the following points should be taken the account.

(i) Placement of the diagram

(ii) Proper labelling.

(iii) Appropriate reference of diagram in the answer.

(iv) Specific requirements in the diagram depending on the type of question e.g.

— Path of rays or positions of object/image for question on optics.

— Direction of electric current in electricity questions.

— Location of charge in electrostatic questions.

— Use of graphs depicting the requirement.

3. Regarding numerical question, the students should be conversant with and so should be told the

following points during the class room teaching:

(i) Possible distribution of marks over value points

(ii) Conversion of units of different physical quantities into same system.

(iii) Use of correct formulas with standard notations, stating their usual meaning.

(iv) Use of diagram, if needed for solving numerical.

(v) Correct substitution of values in the formula and calculation of result in proper form.

(vi) Expression of result in proper unit.

4. While defining a physical quantity it should be taken that it can be defined ‘qualitatively’ as well as

quantitively. Student should not confuse between actual definition and its mathematical expression..

For some physical quantities (e.g. magnetic moment), unit of the quantity should correspond to the

definition stated.

(86)

5. All answer should be ‘‘brief and to the point’’. The expected depth of the answers should be to the

extent given in the prescribed text books. Irrelevant or unnecessary long answers involve wastage of

time. Length of the answer is usually related with the marks

The number of words mentioned in the question papers for different types of answers are only

suggestive. If may be difficult to write the answers within this specified number of words sometimes.

Irrespective of the word limit an answer must contain the desired matter. This should be made clear to

students in the class.

6. If a student is unable to understand or ascertian about the requirement of a question it is advisable that

the other version of the question (Hindi/English) may be read. A student has to identify the ‘action

verb’or the key word in the question which specifies the task.

7. It is advisable that students should be fully conversant with the ‘Design’of the question paper and the

different parameters involved in it ( length of answers, objectives, difficulty level, unit wise

marks etc).

Astudy of erformance analysis of students in physics, C. B. S. E. Delhi.

e.g

Source: P

(87)

CHAPTER-10

EDUCATIONAL RESOURCES ON INTERNET

Department of education, Government of India

University Grant Commission

Information and Library Network Centre

Academics-India

National Informatics Centre

Educational Institutions Resource Bank of India

All India Council forTechnical Education

National Council ForTeacher Education

National Council of Educational Research and Training

Zeelearn-The Complete Learning Portal

Schools ahead

Entrance Booster

http://www.education.nic.in

http://www.ugc.ac.in

http://www.inflibnet.ac.in

www.academics-india.com

http://www.nic.in

http://www.indiaedu.com

http://www.aicte.com

http://www.ncte-in.org

http://www.ncert.nic.in

http://www.zeelearn.com

http://www.schoolsahead.com

http://www.entrancebusters.com

(88)

PHYSICS RESOURCES ON INTERNET

http://www.phys.washington.edu/groups/peg/index.html

http://www.howstuffworks.com/

http://www.tryscience.org

http://www.physics.org/

http://www.physicsgre.com/

http://www.smartkidssoftware.com/ndpir1.htm

http://www.bcspanthers.org/physicswebsites.htm

http://www.learner.org/exhibits/parkphysics/resources.html

http://www.phy.bris.ac.uk/groups/particle/PUS/Teachers.html

http://www.teachingideas.co.uk/science/contents.htm

http://www.teach-nology.com/ teachers/subject_matter/science/physics/

http://shs.westport.k12.ct.us/mjvl/science/physicsweb.htm

http://serendip.brynmawr.edu/sci_edu/

(89)

physics book Output - DelE Directorate of...

Documents

Transcript of physics book Output - DelE Directorate of...