## Monday, January 31, 2011

### Demo Chapters from Vidya Drishti - A site by IITitans for IIT aspirants

DEMO CHAPTERS

• SHM 1 (PowerPoint presentation; best viewed in office 2007)

• Coulomb's Law (PowerPoint presentation; best viewed in office 2007

• Solved problems of kinematics (PowerPoint presentation; best viewed in office 2007)

• Solved problem of Newton's Laws (pdf file)

Find more and purchase course materials online at http://www.vidyadrishti.com

## Friday, January 28, 2011

### A problem from light for class X

Sudhanshu Misra posted:
"An object is placed at a distance of 10cm from convex mirror of focal length15cm; find the position and nature of image?"

Ans:

f= 15 cm

u=-10 cm

v=?

substitute the values in the relation

$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$

and get the value of v as 6 cm

The image is virtual, erect and diminished

### Some sample questions from Physics for SA 2 of CCE class X

1. List the three phenomenon responsible for the formation of rainbow. (Ans: Refraction, Dispersion, (Total)Internal reflection)

2. Why do stars twinkle, but planets do not? (Ans: The twinkling is caused by the variation of intensity of light entering our eye from the stars. The starts are far away from us and they are seen in a position different from their actual position caused by atmospheric refraction. The position goes on shifting slightly due to changes in atmospheric conditions, changing the intensity of light received by the eyes. But the planets are relatively closer to us and further they do not emit their own light. The apparent changes in position due to atmospheric refraction is also not considerable. So, planets do not twinkle)

3. What is meant by power of accommodation of human eye? (The ability of human eye to focus on near by objects as well as far off objects without any time lag is called accomodation and the maximum change in the power of human eye during this process is called power of accomodation; and is equal to 4D)

More questions will be posted soon

### Why we can’t see the stars, towards the horizon?

"i want to know, why we can’t see the stars, towards the horizon?
but we can see stars towards the zenith?

Ans:

Such an observation occurs at twilight. The main culprit here is the comparative greater distance of horizon as compared to zenith.

## Thursday, January 27, 2011

### what is the thermal conductivity of a perfect conductor?

"What is the thermal conductivity of a perfect conductor?"

Ans:

Please check the link below for a detailed list of thermal conductivities of different materials.

http://en.wikipedia.org/wiki/List_of_thermal_conductivities

Every good conductor has some thermal conductivity - low or high. Just like superconductor, thermal conductivity may become infinity for a Thermal Superconductor. Thermal Superconductors may become a reality using CNT (nanotubes)

## Wednesday, January 26, 2011

### KVS Chennai Region Physics Preboard II Question Paper

Please click the link below to download the Question paper for Class XII (Aissce) Preboard Examination conducted by Kendriya Vidyalaya Sangathan, Chennai Region.

Physics preboard Question Paper KVS Chennai Region

## Tuesday, January 25, 2011

### A numerical problem from Beats

1. "A source of sound frequency 256Hz is moving rapidly towards a wall with a velocity of 5m/s. How many beats per second will be heard if sound travels at a speed of 330m/s?"

2. a wire of length 140 cm and mass 0.52×10- kg is stretched by means of a load of 16 kg. Calculate the frequency of the fundamental node?

Ans:

### Interference is in complete agreement to law of conservation of energy

Tilak gurjar posted;
"Interference is in complete agreement to law of conservation of energy. Comment"

If there were no interference, the resultant intensity at a point illuminated by two sources will be

I = I1+I2

Due to interference
$I_{max}=I_{1}+I_{2}+2\sqrt{I_{1}I_{2}}$
$I_{min}=I_{1}+I_{2}-2\sqrt{I_{1}I_{2}}$
$I_{average}=\frac{I_{max}+I_{min}}{2}=\frac{2I_{1}+2I_{2}}{2}=I_{1}+I_{2}$

This shows that energy is conserved even after interference. There is only a redistribution of energy. There is no loss or gain of energy

## Wednesday, January 19, 2011

### Study On Net Will Be Possible For All In Next Two Years: Kapil Sibal

According to the Union Human Resource Development Minister Kapil Sibal, the government has planned to lay out fibre obtics connecting every village and city of India to facilitate students opt for education right from their homes in the next two years. All the colleges will be linked to the top universities in the country through Internet. The expenditure for the project has been estimated to be around Rs 1,000 crore. The move will help about 20 crore students who have no access to higher education today

## Monday, January 17, 2011

### A large field is possible by inserting a soft iron core inside the solenoid. Explain why?

A large field is possible by inserting a soft iron core inside the solenoid. Explain why?

Ans:

Soft Iron has high magnetic permeability, so all the magnetic field lines prefer to pass through it. Thus the magnetic field inside the solenoid is intensified.

CBSE_EXAM_X_2011

## Sunday, January 9, 2011

### CBSE CLASS XII EXAMINATION (AISSCE) 2011 TIME TABLE

CBSE PUBLISHED THE TIM E TABLE FOR AISSCE 2011.

TIME TABLE FOR CBSE CLASS XII EXAM 2011 AISSCE