Monday, July 30, 2012

What's New?!


Hello PhysicsFans!


Let us explain what are the new developments at

English: The logo of the blogging software Wor...Image representing Drupal as depicted in Crunc...

Now we have changed the platform from Drupal to Wordpress - as we thought that content is more important than the structure and other extensive capabilities offered by the Drupal system.

We are now in the process of tweaking the wordpress system to provide all the features and facilities (and some thing more!) we provided earlier with the drupal system.

How to use now?

The first step is to join the site. When you register and then log in to the system, your account will be upgraded to contributor so that you can add blogs and participate on forums. You can post blogs, forum topics and replied to forum posts, but your posts and replies will appear on the site only after ADMIN approves your posts and Replies.

Please suggest more additions and desired features here. We are waiting to hear from you!

Sunday, July 29, 2012

Want your suggestions!

Hello PhysicsFans!

We would like to hear from you. How would you like to improve

Just post your suggestions as comments to this post.

PhysicsFans is undergoing some changes - Please bear with us

Hello PhysicsFans!

As you can see now, PhysicsFans is undergoing some changes - to make the system more stable and rewarding. So, you may face some difficulty.


But, don't worry; We believe that if there is to be a change, it must be for the better if not for the best.


So, just enjoy the changes.

Please don't forget to re - register to the new version to enjoy PhysicsFans to its fullest.

Thursday, July 26, 2012

Transistor as a switch - Question received via Voicemail

[caption id="" align="alignright" width="160"]BJT working as a switch. BJT working as a switch. (Photo credit: Wikipedia)[/caption]

We received the Question "Please explain the working of a transistor as a switch" via email

The answers can be found from the following links.


If you have further doubts, please post them as comments

Wednesday, July 18, 2012

Solutions to HC Verma's Concepts of Physics - Weblinks

We found the following website links which offer solutions to HC Verma's Concepts of Physics.

Though there are some errors and omissions, these links will help at least get ideas which lead towards the solution. Students are advised to try to solve the problems themselves and consult the solution only if they are not getting the correct answer. Please satisfy your own knowledge and understanding before believing on any online solutions.

Please bring to our notice if you find any error in these online solutions.

Weblinks for Solutions to H C Verma's Concepts of Physics









Rotational Mechanics - HC Verma's Concepts of Physics - Solution

HC Verma's Concepts of Physics - Chapter 10 - Question 15

Find the moment of inertia of a uniform square plate of mass m and edge a about one of its diagonals.

The question was posted by Ankit



Let the moment of inertia about the axis through the centre of the square plate perpendicular to the plane, assumed to be along Z axis, be I. Now the square plate will be in the XY plane. Let the X axis and Y axis be parallel to the edges and passing through the centre.

Then, we know that Ix = Iy = ma2/12

Then, according to perpendicular axis theorem,

Iz = Ix + Iy = 2Ix=2ma2/12=ma2/6

Now, imagine that X and Y axes are along the diagonals. (The diagonals of a square are also mutually perpendicular.)

Again, according to perpendicular axis theorem, Iz = Ix + Iy = 2Ix

The MI about the diagonal about its diagonal, Ix = Iz/2 = ma2/12


Tuesday, July 17, 2012

What do you mean by pure spectrum?

A specttrum in which there is no overlapping of different colours is called a pure spectrum.

English: Triangular prism causing the dispersi...

How can we produce a pure spectrum?

For the production of pure spectrum, it is necessary that the slit should be narrow and the incident beam of light should be parallel. Then the emergent rays will be parallel to each other and will be focussed at a point by the telescope. Also, the rays of different wavelengths will be focussed at different points.

Monday, July 16, 2012

Five marks questions from Electronic Devices (Long Answer Type)

  1. Explain the formation of energy Bands in solids. Distinguish between metals, insulators and semiconductors on the basis of band theory.

  2. Distinguish between intrinsic and extrinsic semiconductors and the conduction in P type and N type semiconductors.

  3. Explain the formation of depletion region and barrier potential in a pn junction.

  4. Draw the circuit diagram used to study the Forward and reverse bias characteristics and draw the graph for forward bias and reverse bias.

  5. Describe the working of a half wave rectifier  with the help of a neat labeled diagram and draw the input and output wave forms.

  6. Describe the working of a full wave rectifier with the help of a neat labelled diagram and draw the input and output wave forms.

  7. Draw the symbols of npn and pnp transistor. Show the biasing of a transistor and explain transistor action. 

  8. Describe the working of an npn transistor in CE configuration as an amplifier.

  9. Explain the working of a transistor in CE configuration as oscillator.

  10. Explain the action of transistor as a switch.

(Have some more idea? Post them as comments)

Doubts on electric field lines and flux

[caption id="" align="alignright" width="180"]English: Field of a positive point charge. Thu... English: Field of a positive point charge. Thumbnail version (Photo credit: Wikipedia)[/caption]

Q1.Is the number of electric feild lines due to a charge DEFINITE?
Q2.If it is infinite, then the electric flux due to a charge should be infinite(flux gives the num. Of elctric feild lines passing through an area)?
Flux should be equal irrespective of the magnitude of charge.
Q3.If it is definite,then it will always be a natural number and cannot be a decimal,but when we take out flux for an Electron,it yeilds a decimal value.
E.flux~ magn. Of charge
Permittivity of Medium
Medium-taken to be vaccum(here).

Mathar Hasan posted

Saturday, July 14, 2012

Best Wishes for CBSE Compartment Exam

Hello students,

CBSE is conducting the compartment exam 2012 on 16 July.

We wish all the candidtaes the very best.

Please keep this in mind while you prepare for the exam.

  • Don't have any presumption that the compartment exam will be easier than the main exam

  • Attempt all questions

  • Ensure that you have attempted all parts of the same question (Even if you don't know it)

  • Attempt the questions whose answers are well known to you and later go on to the less known one.

  • Please make sure that you have written the correct question number.

  • Draw diagrams using instruments. (Free hand diagrams will not fetch good marks)

  • While attempting numericals, write data giving proper symbols first and then write formula. Then you may be able to solve the problem which you thought you may not be able to solve at all!

Once again


Central Board of Secondary Education