## Thursday, September 30, 2010

### A Numerical Problem from motion

A small smooth object slides down a smooth incline plane, inclined at am angle 30 to the horizontal. What is

• the acceleration down the plane?
• The time to reach the bottom if the plane is 50m long?

The object is now thrown up the plane with an initial velocity me 15m/s ; how long does it take to object to come to rest and how far up the plane has the object then travelled?

(Students and visitors are requested to attempt and post the answers as comments. The master will answer the question soon)

## Wednesday, September 29, 2010

### Download AISSCE 2011 Sample Papers for Class XII CBSE

Practising sample papers, model papers and previous question papers is the easiest and fool proof way of scoring big in exams. Here you can find the sample papers published by CBSE for candidates for AISSCE 2011

Physics - Paper-I |   Paper-II |   Paper-III

## Tuesday, September 28, 2010

### Collisions and Principle of Conservation of Momentum - Weblinks

According to the principle of conservation of momentum, the total momentum of a system of particles remains constant provided no external force acts on it.

Principle of conservation of momentum is one of the fundamental concepts of Physics.

### Alternating Current Circuits and EM Waves Test Paper (KV Pattom)

Download the test paper from Alternating Current and Electromagnetic Waves (Class XII Physics)

AC & EM Waves Test Paper

### General :

A.The extensive use of the calculus (differentiation and integration) and the use of complex numbers or solving differential equations should not be required to solve the theoretical and practical problems.

B.Questions may contain concepts and phenomena not contained in the Syllabus but sufficient information must be given in the questions so that candidates without previous knowledge of these topics would not be at a disadvantage.

C.Sophisticated practical equipment likely to be unfamiliar to the candidates should not dominate a problem. If such devices are used then careful instructions must be given to the candidates.

D.The original texts of the problems have to be set in the SI units.

A. THEORETICAL PART

1. MECHANICS

a] Foundation of kinematics of a point mass

* Note: vector description of the position of the point mass, velocity and acceleration as vectors

b] Newton's laws, inertial systems

* Note: problems may be set on changing mass

c] Closed and open systems, momentum and energy, work, power

d] Conservation of energy, conservation of linear momentum, impulse

e] Elastic forces, frictional forces, the law of gravitation, potential energy and work in a gravitational field

* Note: Hooke's law, coefficient of friction (F/R=const), frictional forces static and kinetic, choice of zero of potential energy

f] Centripetal acceleration, Kepler's laws

2] MECHANICS OF RIGID BODIES

a] Statics, center of mass, torque

* Note: couples, conditions of equilibrium of bodies

b] Motion of rigid bodies, translation, rotation, angular velocity, angular acceleration, conservation of angular momentum

* Note: conservation of angular momentum about fixed axis only

c] External and internal forces, equation of motion of a rigid body around the fixed axis, moment of inertia, kinetic energy of a rotating body

* Note: parallel axes theorem (Steiner's theorem), additivity of the moment of inertia

d] Accelerated reference systems, inertial forces

* Note: knowledge of the Coriolis force formula is not required

3] HYDROMECHANICS

No specific questions will be set on this but students would be expected to know the elementary concepts of pressure, buoyancy and the continuity law.

4] THERMODYNAMICS AND MOLECULAR PHYSICS

a] Internal energy, work and heat, first and second laws of thermodynamics

* Note: thermal equilibrium, quantities depending on state and quantities depending on process

b] Model of a perfect gas, pressure and molecular kinetic energy, Avogadro's number, equation of state of a perfect gas, absolute temperature

* Note: also molecular approach to such simple phenomena in liquids and solids as boiling, melting etc.

c] Work done by an expanding gas limited to isothermal and adiabatic processes

* Note: proof of the equation of the adiabatic process is not required

d] The Carnot cycle, thermodynamic efficiency, reversible and irreversible processes, entropy (statistical approach), Boltzmann factor

* Note: entropy as a path independent function, entropy changes and reversibility, quasistatic processes

5] OSCILLATIONS AND WAVES

a] Harmonic oscillations, equation of harmonic oscillation

* Note: solution of the equation for harmonic motion, attenuation and resonance - qualitatively

b] Harmonic waves, propagation of waves, transverse and longitudinal waves, linear polarization, the classical Doppler effect, sound waves

* Note: displacement in a progressive wave and understanding of graphical representation of the wave, measurements of velocity of sound and light, Doppler effect in one dimension only, propagation of waves in homogeneous and isotropic media, reflection and refraction, Fermat's principle

c] Superposition of harmonic waves, coherent waves, interference, beats, standing waves

* Note: realization that intensity of wave is proportional to the square of its amplitude. Fourier analysis is not required but candidates should have some understanding that complex waves can be made from addition of simple sinusoidal waves of different frequencies. Interference due to thin films and other simple systems (final formulas are not required), superposition of waves from secondary sources (diffraction)

6] ELECTRIC CHARGE AND ELECTRIC FIELD

a] Conservation of charge, Coulomb's law

b] Electric field, potential, Gauss' law

* Note: Gauss' law confined to simple symmetric systems like sphere,cylinder, plate etc., electric dipole moment

c] Capacitors, capacitance, dielectric constant, energy density of electric field

7] CURRENT AND MAGNETIC FIELD

a] Current, resistance, internal resistance of source, Ohm's law, Kirchhoff's laws, work and power of direct and alternating currents, Joule's law

* Note: simple cases of circuits containing non-ohmic devices with known V-I characteristics

b] Magnetic field (B) of a current, current in a magnetic field, Lorentz force

* Note: particles in a magnetic field, simple applications like cyclotron, magnetic dipole moment

c] Ampere's law

d] Law of electromagnetic induction, magnetic flux, Lenz's law, self-induction, inductance, permeability, energy density of magnetic field

* Note: magnetic field of simple symmetric systems like straight wire, circular loop and long solenoid

e] Alternating current, resistors, inductors and capacitors in AC-circuits, voltage and current (parallel and series) resonances

* Note: simple AC-circuits, time constants, final formulae for parameters of concrete resonance circuits are not require

8] ELECTROMAGNETIC WAVES

a] Oscillatory circuit, frequency of oscillations, generation by feedback and resonance

b] Wave optics, diffraction from one and two slits, diffraction grating, resolving power of a grating, Bragg reflection

c] Dispersion and diffraction spectra, line spectra of gases

d] Electromagnetic waves as transverse waves, polarization by reflection, polarizers

* Note: superposition of polarized waves

e] Resolving power of imaging systems

f] Black body, Stefan-Boltzmanns law

* Note: Planck's formula is not required

9] QUANTUM PHYSICS

a] Photoelectric effect, energy and impulse of the photon

* Note: Einstein's formula is required

b] De Broglie wavelength, Heisenberg's uncertainty principle

10] RELATIVITY

a] Principle of relativity, addition of velocities, relativistic Doppler effect

b] Relativistic equation of motion, momentum, energy, relation between energy and mass, conservation of energy and momentum

11] MATTER

a] Simple applications of the Bragg equation

b] Energy levels of atoms and molecules (qualitatively), emission, absorption, spectrum of hydrogenlike atoms

c] Energy levels of nuclei (qualitatively), alpha-, beta- and gamma-decays, absorption of radiation, halflife and exponential decay, components of nuclei, mass defect, nuclear reactions.

B. PRACTICAL PART

The Theoretical Part of the Syllabus provides the basis for all the experimental problems. The experimental problems given in the experimental contest should contain measurements.

1] Candidates must be aware that instruments affect measurements.

2] Knowledge of the most common experimental techniques for measuring physical quantities mentioned in Part A.

3] Knowledge of commonly used simple laboratory instruments and devices such as calipers, thermometers, simple volt-, ohm- and ammeters, potentiometers, diodes, transistors, simple optical devices and so on.

4] Ability to use, with the help of proper instruction, some sophisticated instruments and devices such as double-beam oscilloscope, counter, ratemeter, signal and function generators, analog-to-digital converter connected to a computer, amplifier, integrator, differentiator, power supply, universal (analog and digital) volt-, ohm- and ammeters.

5] Proper identification of error sources and estimation of their influence on the final result(s).

6]Absolute and relative errors, accuracy of measuring instruments, error of a single measurement, error of a series of measurements, error of a quantity given as a function of measured quantities.

7] Transformation of a dependence to the linear form by appropriate choice of variables and fitting a straight line to experimental points.

8] Proper use of the graph paper with different scales (for example polar and logarithmic papers).

9] Correct rounding off and expressing the final result(s) and error(s) with correct number of significant digits.

10] Standard knowledge of safety in laboratory work. (Nevertheless, if the experimental set-up contains any safety hazards the appropriate warnings should be included into the text of the problem.)

• The syllabus for  National Standard Examination in Physics (NSEP) is broadly  equivalent to the senior secondary level (Class XI and Class XII) of CBSE Physics. This is only a rough guideline, and there is no detailed syllabus given for NSEP.
• The syllabus for Indian National Physics Olympiad (INPhO) is broadly similar to NSEP but the difficulty level of the questions will be higher. Questions and problems in National Olympiads are usually non-conventional and of high difficulty level, comparable to International Olympiads.

## Wednesday, September 22, 2010

### Online Competitions (For all students of schools affiliated to CBSE): Common Wealth Games 2010

The official website of Delhi Tourism is www.delhitourism.gov.in and students can log on to the website for participating in various activities on it.
The activities given on the website are :
• Good Deed indeed (Good Deed done by children)
• To my favorite Sports Star (Wish and write messages)
• Dress up your home for CWG 2010 (take CWG festivities to the home and school)
• There is Something I want to change! (children give solutions to civic issues).

SHERA MERA DOST GUIDELINES
The Commonwealth in Education Programme for Delhi 2010

“Shera Mera Dost ”
My Friend Shera

It’s time for all children to come out and take part in CWG 2010!
PROGRAMME GUIDELINES FOR SCHOOLS AND EDUCATION OFFICIALS
INTRODUCTION

## Friday, September 17, 2010

### SUSPENDED TYPE GALVANOMETER ANIMATION

A moving coil galvanometer is an instrument used for detection and measurement of small electric currents. Principle A current carrying conductor placed in a magnetic field experiences a torque. See Animation

### Cyclotron Animation

A cyclotron is device by which positively charged particle can be accelerated and the desired nuclear reaction can be brought about.

#### Principle

A positively charged particle can be accelerated to high energy with the help of an oscillating electric field, by making it cross the same electric field time and again with the use of a strong magnetic field.

#### Construction

It consists of two dees or D-shaped metal chambers D1 and D2. The dees are separated by a small distance. The two dees are perpendicular to their plane. P is the position where the ion source is placed.

The dees are maintained to a potential difference whose polarity alternates with the same frequency as the circular motion of the particles. The dees are closed in a steel box placed between the poles of a strong electromagnet. The magnetic field is perpendicular to the plane of the dees.

See Animation

## Thursday, September 16, 2010

### CBSE Class X SA 1 conducted under CCE

Image via Wikipedia

Download CBSE Class X SA 1 2010 - 2011conducted under CCE by KVS Chennai Region

Given in both English and Hindi

CBSE X SA I Science 2010 - 2011

## Monday, September 13, 2010

### SOUND

Important points

• Sound is a form of energy which produces the sensation of hearing.
• Sound is produced due to vibrations in the body and travels in all directions away from the source.
• Sound requires a medium for propagation. It cannot travel in vacuum.
• Sound travel faster in solid than in liquids or gases. The velocity of sound is maximum in case of solids, lesser in the case of liquids and least in the case of gases.
• The repetition of sound, when it is reflected from a distant body is called an echo.
• Sonar is an instrument used for the measurement of the depth of sea. It is based on the principle of reflection of sound (echo).
• Sounds having frequencies lower than 20 hertz are called infrasonic sounds.
• Sounds having frequencies higher than 20,000 hertz are called ultrasonic sounds.
• Sounds are generally classified into two broad categories (a) musical sound (b) noise.
• Musical sound produces a pleasant effect in the ears. It is produced by periodic vibrations.
• Noise produces an unpleasant effect to the ears. It is produced by non periodic vibrations.
• The characteristics of sound which makes the sounds different from one another are (a) loudness (b) pitch and © quality or timbre.
• The loudness of a sound produced by a body depends on (a) its amplitude (b) area of the vibrating body © distance between the source and the listener.
• The pitch of the sound produced by a body depends on the frequency of vibration – greater the frequency of vibration greater is the pitch.

## Friday, September 10, 2010

### Optional Proficiency Test for Class-X

CBSE is conducting an optional proficiency test in all the five main subjects from next year.

The proposed Proficiency Test is being conducted with the broad objectives of :

• acting as a benchmark in testing of skills and higher mental abilities of students
• providing motivation to students for academic excellence in the respective subject
• providing feedback to students and parents on how well the students have achieved the desired learning objectives.
• providing feedback to schools on levels of learning of their students and setting
• goals, priorities and targets in their future educational plan.

Some of the specific objectives of the proposed test include assessing students;

• abilities and skills to apply concepts and principles of the subject to everyday life situations.
• abilities to apply understanding of concepts to interpret data, diagrams, maps, graph etc.
• skills to create and devise methods for solving subject related problems.
• abilities to analyse, synthesise and evaluate a given situation on the basis of learning in the subject.

What is a Proficiency Test?
A proficiency Test measures an individual’s abilities and skills in a domain or subject to know how well he/she has learned, understood and internalised the related concepts and principles. Such a test in language e.g may assess a student’s skills in reading, writing, listening, speaking or vocabulary. Similarly a test in Science may focus on assessing students’ abilities to apply concepts and principles to analyse a given situation, solve a given problem and conduct practical work efficiently. A test in Mathematics may similarly assess problem solving abilities and skills of mathematical thinking, mathematical reasoning and procedural techniques followed by students. Thus, the proposed Proficiency Test will mainly focus on assessing students’ abilities and skills to apply knowledge and understanding of any subject to new and unfamiliar everyday life situations.
The core testing element of such a test will include observing, comparing, classifying, solving, translating, interpreting, analyzing, synthesising, creating, composing, deducing, justifying and judging/evaluating.

General Features of the Test
It will be optional in nature. Only those students who wish to take this test willingly may appear.
There will be separate test in each of the five main subjects viz English, Hindi, Social Science, Mathematics and Science.
A student may appear in one or more subject (s) according to his/her choice. One test will be held on a single day.
It will be a paper-pen test to be administered on the same day across all willing schools in the country.
The proposed test is likely to be conducted in the month of May/June next year (2011).

Students wishing to appear in the test will have to pay separate examination fee for the same. This fee is likely to be in the range of Rs.500/- to Rs.1000/- for all the subjects. The schools will be informed about the exact amount of fee and its submission mode at a later stage.
Any student studying in Secondary or Senior secondary school affiliated to CBSE and has appeared in Class-X final examination (School conducted or Board conducted ) is eligible for this test.
Students appearing in the test will be issued a joint certificate by CBSE and the collaborating agency indicating percentile rank.
Design of the Question Paper
The duration of the test in every subject will be 2½ hours.
Question paper in every subject will carry 100 marks
All questions will be of multiple choice type with only single correct answer.
The test will be based on classes IX-X syllabus in the subject prescribed by CBSE

The typology of questions will be different from the type of questions asked in conventional final examination conducted by the Board at the end of Class-X. The test will not include any direct recall, information-based or memory –based questions. It will only include questions to assess students’ skills and abilities to apply understanding of concepts to analyse a given situation or an unfamiliar
everyday life problem.
The total number of questions may vary from one subject to another.
The questions included in the question paper will be of varying difficulty level.
Negative marks will be awarded for wrong answers

### Weightless Wonder : Reduced Gravity Flight

Follow the link below to watch and download NASA’s article on Reduced gravity flights

### Weightless Wonder : Reduced Gravity Flight

Follow the link below to watch and download NASA’s article on Reduced gravity flights

### Light Glossary

A primary light color—red, blue, or green; these three colors produce white light when
angle of incidence
The angle between a wave striking a barrier and the line perpendicular to the surface.
angle of reflection
The angle between a reflected wave and the normal to the barrier from which it is reflected.
angstrom
An angstrom is 1/100,000,000 of a centimeter.
concave lens
A lens that is thinner in the middle than at the edges; used to correct nearsightedness.
convex lens
A lens that is thicker in the middle than at the edges; used to correct farsightedness.
diffraction grating
A piece of transparent or reflecting material, which contains many thousands of parallel
lines per centimeter; used to produce a light spectrum by diffraction.
electromagnetic wave
A wave that does not have to travel through matter in order to transfer energy.
electromagnetic spectrum
Transverse radiant energy waves, ranging from low frequency to very high frequency,
which can travel at the speed of light.
element
A substance that cannot be broken down into simpler substances by ordinary means.
equalateral triangle
A triangle with three equal angles of 60 degrees and sides of equal length.
filter
A screen that allows only certain colors to pass through it; a transparent material that
separates colors of light.
focal length
The distance between the principal focus of a lens or mirror and its optical center.

focal point/focus
The point that all light rays from a mirror or lens pass through.
frequency
The number of waves that pass a point in a given unit of time.
gamma ray
High-energy wave of high frequency and with a wavelength shorter than an x ray; released
in a nuclear reaction.
image
The reproduction of an object formed with lenses or mirrors.
in phase
When two or more light rays overlap exactly at the crest and the trough, they are said to be
“in phase.”
index of refraction
The amount that light is refracted when it enters a substance; given as the ratio of speed
of light in a vacuum to its speed in a given substance.
Invisible radiation with a longer wavelength than red light and next to red light in the
electromagnetic spectrum; used in heat lamps, to detect heat loss from buildings, and to
detect certain tumors.
interference
The addition by crossing wave patterns of a loss of energy in certain areas and reinforcement
of energy in other areas.
kaleidoscope
A toy in which reflections from mirrors make patterns. It was invented in 1819
by David Brewster.
laser (light amplification by stimulated emission of radiation)
A device that produces a highly concentrated, powerful beam of light which is all one
frequency or color and travels only in one direction.
law of reflection
Angle of incidence equals the angle of reflection.
lens
A curved, transparent object; usually made of glass or clear plastic and used to direct light.

light
Light is a form of energy, traveling through the universe in waves. The wavelengths of visible
light range from less than 4,000 angstroms to more than 7,000 angstroms.
normal
A line perpendicular to a surface.
opaque
Not transparent; no light passes through the material.
optical axis
The line straight out from the center of a parabolic mirror; straight line through the center of
a lens.
optical fiber
A thin strand of glass that transmits light down its length.
optical telescope
A tube with magnifying lenses or mirrors that collect, transmit, and focus light.
out of phase
When the crest of one wave overlaps the trough of another they are said to be “out of phase.”
parabola
A curved line representing the path of a projectile; the shape of the surface of a
parabolic mirror.
parabolic mirror
A curved mirror.
pigment
A material that absorbs certain colors of light and reflects other colors.
plane mirror
A mirror with a flat surface.
polarized light
Light in which all waves are vibrating in a single plane.
prism
A transparent material with two or more straight faces at an angle to each other.
real image
An image that can be projected onto a screen; formed by a parabolic mirror or convex lens.

reflection
The light or image you see when light bounces off a surface; bouncing a wave or ray off a surface.
reflecting telescope
A telescope in which magnification is produced by a parabolic mirror.
refraction
Bending of a wave or light ray caused by a change in speed as it passes at an angle from one
substance into another.
scattering
The spreading out of light by intersecting objects, whose size is near the wavelength.
spherical
Surface of a lens or mirror that is part of a sphere.
subtractive color
One of the three pure pigment colors—magenta, yellow, cyan; these pigment colors produce
black when mixed.
translucent
Semitransparent; a material that admits some light.
transparent
See-through; light can go through.
true image
A true image is the way other people see us. It is the opposite of the image that is seen in a
mirror.
Radiation that has a shorter wavelength than visible light; next to violet light in the
electromagnetic spectrum.
virtual image
An image formed by a mirror or lens that cannot be projected onto a surface.
visible light spectrum
Band of visible colors produced by a prism when white light is passed through it.
wavelength
The total linear length of one wave crest and trough.
x ray
Invisible electromagnetic radiation of great penetrating power.

### Introduction to Light - NASA

Light is a form of radiant energy or energy that travels in waves. Since Greek times, scientists have  debated the nature of light. Physicists now recognize that light sometimes behaves like waves and, at other times, like particles. When moving from place to place, light acts like a system of waves. In empty space, light has a fixed speed and the wavelength can be measured. In the past 300 years,
scientists have improved the way they measure the speed of light, and they have determined that it travels at nearly 299,792 kilometers, or 186,281 miles, per second.
When we talk about light, we usually mean any radiation that we can see. These wavelengths range from about 16/1,000,000 of an inch to 32/1,000,000 of an inch. There are other kinds of radiation such as ultraviolet light and infrared light, but their wavelengths are shorter or longer than the visible light wavelengths. When light hits some form of matter, it behaves in different ways. When it strikes an opaque object, it makes a shadow, but light does bend around obstacles. The bending of light
around edges or around small slits is called diffraction and makes patterns of bands or fringes.
All light can be traced to certain energy sources, like the Sun, an electric bulb, or a match, but most
of what hits the eye is reflected light. When light strikes some materials, it is bounced off or reflected. If the material is not opaque, the light goes through it at a slower speed, and it is bent or refracted. Some light is absorbed into the material and changed into other forms of energy, usually heat energy. The light waves make the electrons in the materials vibrate and this kinetic energy or movement energy makes heat. Friction of the moving electrons makes heat.

## Tuesday, September 7, 2010

### What is IAPT? NSEP? NSEC? NSEB? NSEA? & NSEJS?

IAPT (Indian Association of Physics Teachers) is an association of Physics Teachers spread through out the country. It was started by Late Dr. D. P.
Khandelwal in 1984 and today it has 5000 life members. All the work of this (our) organization is voluntary in character-thus NOBODY is paid any Honorarium or remuneration for ANY WORK of IAPT.
What is NSEP? NSEC? NSEB? NSEA? & NSEJS?

National Standard Examinations (NSEP in Physics, NSEC in Chemistry, NSEB in Biology, NSEA in Astronomy and NSEJS in Junior Science) are nationwide examinations organised by IAPT. IAPT has been conducting NSEP for last 24 years by now. NSEP, NSEC, NSEB, and NSEA are at CBSE class XII level, while NSEJS is at CBSE class X level. These examinations are the FIRST and THE
ONLY SCREENING TESTS towards International Olympiads in the respective subjects.

### What are Science Olympiads?

International Olympiads are held every year in Mathematics, Physics, Chemistry, Biology, Astronomy and Junior Science. Olympiads are internationally recognized competitions in various fields of knowledge. They are the highest level examinations and are hosted by different countries every year. Participation in any of the Olympiads has worldwide recognition and is considered as a great achievement.
How do I go to (or participate in) the Physics (or Chemistry or Biology or Astronomy or Junior Science) Olympiad ?

You will have to appear for NSEP (or NSEC / NSEB / NSEA / NSEJS) - be in the top 300 students and then through the Indian National Physics Olympiad
INPhO (or INChO or INBO or INAO or INJSO) you may be selected for the further stages of the respective International Olympiad Programme.

### How do I enrol myself for any of these?

You must register from your OWN School/College. The Principal (or Physics / Science teacher) of your College/ Jr. College / High School will enroll you.
He will give you all further instructions. In case you have any difficulty, refer to our website www.iapt.org.in. List of all NSE centers of last year (2009-2010) is available on this website. The name of contact person at the respective center, is also indicated. Enrolment is at the centers only. No  direct enrolment.

What are the fees?
Rs. 75/- per student per subject (per examination) to be paid to the center incharge. DO NOT SEND ANY MONEY TO IAPT OFFICE. This exam fee cannot be refunded.

### Are old Question papers available for olympiads?

Physics, Chemistry, Biology and Astronomy : Set of last four years question papers with answers / solutions of NSEP, NSEC ,NSEB and NSEA is available. To get this, send a DD of Rs. 100/- in favour of IAPT, payable at Pune, to our office. The set will be dispatched by regd. post/courier. Write your name and complete postal address on the back of DD.
Junior Science : A set of last two years question papers with solutions is available. To get this, Send a DD of Rs.50/- in favour of IAPT, payable at Pune, to our office. The set will be dispatched by regd post / courier. Write your name and complete postal address on the back of DD.
Prof. R. M. Dharkar,
Chief Co-ordinator
Prof. M. L. Ogalapurkar,
NSEP/NSEC/NSEB Co-ordinator
Prof. J. P. Gadre,
NSEA/ NSEJS Co-ordinator
I.A.P.T. Office, I.I.E. Campus,
128/2, J. P. Naik Marg, Kothrud,
PUNE - 411 038
Tel. (Off.) 020 - 2542 0163;
e-mail iapt@vsnl.net;
Website : www.iapt.org.in

### National Standard Examinations in PHYSICS, CHEMISTRY, BIOLOGY, ASTRONOMY

National Standard Examinations in PHYSICS, CHEMISTRY, BIOLOGY,ASTRONOMY(NSEP, NSEC, NSEB, NSEA at Std XII level) and National Standard Examinations in JUNIOR SCIENCE NSEJS at Std X level

### QUESTIONS FOR CLASS X CCE SA1 PHYSICS

QUESTION:
Two metallic wires A and B of the same material are connected in parallel. Wire A has length l and radius r, wire B has a length 2l and radius 2r. Calculate the ratio of the equivalent resistance in parallel combination and the resistance of wire A.

### CBSE CLASS X CCE: QUESTIONS FOR SA 1

QUESTION: In a household electric circuit different appliances are connected in parallel to one another. Give two reasons.
An electrician puts a fuse of rating 5A in that part of domestic electrical circuit in which an electrical heater of rating 1.5kW, 220V is operating. What is likely to happen in this case and why? What change, if any, needs to be made?
ANSWER: (i) The appliances can be operated independently.
(ii) They get the same applied voltage
The fuse will not blow off even if the current in these devices were to exceed their safe current value.
This could damage these devices and even cause fire.
Any fuse of lower amperage needs to put in the circuit

### CBSE CLASS X : QUESTIONS FOR SA 1

QUESTION: What is biogas? How is it obtained from biomass? Why is biogas considered an ideal fuel?

ANSWER: Biogas is a mixture of methane, carbon dioxide, hydrogen and hydrogen sulphide. Biogas is obtained by anaerobic decomposition of biomas.
1. Heating Capacity high
2. Burnes without smoke
3. Leaves no residue
4. Slurry left behind can be used as a manure

### SAMPLE QUESTIONS FOR SA 1 PHYSICS

QUESTION: Out of two solar cookers, one was covered with a plane glass slab and the other was left open. Which of the two solar cookers will be more efficient and why?

: The solar cooker with the glass slab: as the heat gets trapped within the cooker and the temperature of the cooker rises. It rises more than the uncovered cooker/green house effect.

### Class X CCE Frequently Asked Questions

Q. Does CCE mean frequent tests and assignments?
CHAIRMAN: The term continuous in CCE refers to periodicity and regularity in assessment. It does not mean that tests and assignments have to be conducted or given frequently. On the
contrary, the scheme of CCE discourages mechanical testing. It envisages employment of variety of tools and techniques for assessment in informal and formal settings which
are more interesting, relevant and meaningful and involve learners for greater participation and learning.

## Saturday, September 4, 2010

### More on Cosmological constant

A constant introduced by Einstein  (1917) into the equations of general relativity to allow a steady state cosmological solution to the Einstein field equations. The constant was introduced before the concept of the Big Bang had been conceived, so an expanding or contracting universe  was regarded as physically implausible, leading Einstein to add as a "fudge factor." In theory, the constant can be derived from quantum field theory, but the derivation has not yet been performed. Einstein's cosmological constant is equivalent to a vacuum energy density, which means it can be put on the left hand side of Einstein's equations with the geometry (as Einstein did), or on the right hand side with the stress-energy, both forms being mathematically equivalent.

The value of in our present universe is not known, and may be zero, although there is some evidence for a nonzero value; a precise determination of this number will be one of the primary goals of observational cosmology in the near future.

The value of the cosmological constant is an empirical issue which will ultimately be settled by observation; meanwhile, physicists would like to develop an understanding of why the energy density of the vacuum has this value, whether it is zero or not. There are many effects which contribute to the total vacuum energy,
including the potential energy of scalar fields and the energy in “vacuum fluctuations” as predicted by quantum mechanics, as well as any fundamental cosmological constant.

If the recent observational suggestions of a nonzero are confirmed, we will be faced with the additional task of inventing a theory which sets the vacuum energy to a very small value without setting it precisely to zero. In this case we may distinguish between a “true” vacuum which would be the state of lowest possible energy which simply happens to be nonzero, and a “false” vacuum, which would be a metastable state different from the actual state of lowest energy (which might well have = 0). Such a state could eventually decay into the true vacuum, although its lifetime could be much larger than the current age of the universe. A
final possibility is that the vacuum energy is changing with time — a dynamical cosmological “constant”. This alternative, which is sometimes called “quintessence”, would also be compatible with a true vacuum energy which was ultimately zero, although it appears to require a certain amount of fine-tuning to make it work.
No matter which of these possibilities, if any, is true, the ramifications of an accelerating universe for fundamental physics would be truly profound.

## Friday, September 3, 2010

### Importance of Cosmological Constant

Understanding the unnaturally small size of the cosmological constant poses one of severest challenges for a theory of gravity. At late times and for large distances, the apparent size of the cosmological constant is constrained to be extremely small in terms of the natural scale for gravity, the Planck mass. In contrast, no observations bound the value of the cosmological constant during the earliest stages of the universe, when corrections to the Einstein-Hilbert action were non-negligible, and its presence can lead to a richer family
of metrics. Among the solutions for a more general gravitational action, the presence of a positive  cosmological constant does not inevitably lead to a de Sitter expansion. Such solutions must still yield or evolve into a low energy theory in which the effective cosmological constant is small to be phenomenologically acceptable. If the characteristic scales on which these metrics vary are of extremely high energy or short distance, then it may be possible to integrate out such features to arrive at a slowly varying e®ective theory.
To determine whether an action for gravity, generalized beyond an Einstein-Hilbert term, admits these features | natural coefficients for the terms in the action and a rapid variation | we must ¯rst solve the highly non-linear field equations. This task is difficult even when only the next curvature corrections are added. In 3 + 1 dimensions, Horowitzand Wald and later Starobinsky [3] discovered oscillating solutions for actions that
included quadratic curvature terms but no cosmological constant. Numerical solutions were found in 4 + 1 dimensions in the presence of a cosmological constant and a scalar field, along with the quadratic curvature terms. In this latter scenario, metrics exist that depend periodically on the extra spatial coordinate so that choosing the size of the extra dimension to be the period produces a compact extra dimension without any fine-tunings or singularities. The parameters in the action ¯x the size of the extra dimension uniquely.
However, without an analytical approach it becomes di±cult to generalize these solutions to include an evolution in time. Without this freedom, it is di±cult to understand how a universe starting from a more general state can  find itself in one of these configurations.

### Cosmological Constant and its Significance

Would you plz explain me what is a cosmological constant? When Einstein snubbed it as the "biggest blunder" in his life, what else is the real importance of the constant? Also what is cosmological acceleration and its' effect on the constant...plz...but in simple words...plzzzz:)))))

Ans:

The cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe.

Einstein abandoned the concept after the observation of the Hubble redshift indicated that the universe might not be stationary, as he had based his theory on the idea that the universe is unchanging.However, the discovery of cosmic acceleration in the 1990s has renewed interest in a cosmological constant.

{courtesy : Wikipedia}

More details will be added soon