Black holes-Not exactly Black!!

Black holes-Not exactly Black!!
Now we have known black holes as giant swirling  holes present in the universe which are known to swallow anything that comes close to it. Yes we have had countless rumors and fantasies about black holes being warps in time , a portal to another dimension and the doorway to a mirror world. Of course black holes don’t really do something like that but that doesn’t mean they are not fascinating by themselves.
The mystery of black holes has fascinated physicists, scientists and certainly many others alike with their mysterious behavior. Their birth, evolution etc. are still under study and are  the objects of obsession of most astrophysicists.
So If it’s not a portal to the next dimension then what is it and where do the objects that it pulls inwards disappear to?
Well think of it this way. You may have heard of how  when a body of mass m and another mass M attract each other with a force given by
And the fact because of this force the potential energy that exists between them is
                                                      P.E. = G.M.m 
And also the fact that escape velocity can be found by equating it with kinetic energy of the object to be equal to it’s potential energy
                                                   K.E.= 0.5 m.v2  
Now equating the kinetic energy with the potential energy we get
                                                 v2 =G. m
Now imagine a mass with gigantic (and i really mean it)  mass and really tiny radius        
such that                                G.M      =c2
where c is the speed of light.
Yes that’s what black holes exactly are. They are objects having mass and sometimes having charge as well as angular momentum such that any object on it will have to travel at the speed of light just to escape.  So that explains why all objects cannot escape the gravitational pull of a black hole. 
Is it that strong?
Well it is so strong that it is known to even absorb light. That’s right! Black holes actually bend gravitational space around it so much that even light cannot escape it’s pulling power. Scientists have named this as the infinite space time curvature!! At this point the state of the system is called singularity. In the state of singularity the some of Einstein’s equations along with some other big equations give weird solutions the details of which i will not bore you with. But what i will say is that any mass near this point of singularity  will have time running down slower for it!(Time travel theories anyone?!!)
Why are scientists so obsessed with it?
Well for one thing they hold vital clues as to the origin of the universe. It’s true. The requirement of the formation of black holes is gigantic mass and small radius. That was the condition of the universe just a few moments before and after the big bang. So when that small point exploded in the event of the big bang many black holes were formed as the universe was expanding. So the black holes we study including the one at the centre of our galaxy is a by product of the big bang. So we can actually figure out where it all began!
So how are they formed?
Well like i told you the big mass and small radius is a good condition for the formation of black holes. So lots of black holes were formed after the big bang. Also lots of black holes are formed when massive stars collapse due to their own gravitational pull.  But of course once formed it doesn’t stay together forever. It slowly decays by means of a radiation called Hawking’s radiation.
So where do these masses disappear into?
Well that is something no one is sure of! Yes that’s true. Nobody really knows what happens to all that sucked up mass. While it is true that a lot of the mass is emitted as energy from the accretion disks.  In fact accretion disks are some of the brightest stuff in the universe. Not so black any more right?
clip_image006But scientists have found that this energy emitted as energy does not equal the energy obtained from the mass energy equivalence (any one remember Einstein’s epoch changing equation? e=mc2) energy obtained from the mass swallowed. (Though it is more efficient than fusion or fission as they use of 0.4% of the mass to be converted to energy while accretion disk formation uses 40% of the relative rest mass!)In fact information is lost inside the black hole. It would have been ok if black holes existed forever but the fact is they don’t. They decay through hawking’s radiation and hence it seems that the information is truly lost. In quantum mechanics this is the same as violation of conservation of energy!
So next time your physics teacher tells you that nothing violates the conservation of energy you might wanna raise your hand and ask him/her about black holes. If he is genuinely interested in learning he will certainly try to help you explain better.

CBSE Physics Solved Board Question Papers 2008, 2009, 2010 & 2011 – All versions

Download CBSE Physics Solved Board Question Papers 2008, 2009, 2010 & 2011 – All versions (Delhi, Outside Delhi & Foreign)

Central Board of Secondary Education

The question Papers are in PDF format, all question papers with solution in a single file. So, it may take some time for the download to finish.

CBSE Physics Class 12 Board Question Papers 2008 to 2011 all sets (SETS I, II & III) and versions (DELHI, FOREIGN, OUTSIDE DELHI)

Click Here to Download. 

Sure Shot questions in Physics for CBSE Class 9 Summative Assessment (SA1)

All CBSE Schools are conducting the SA1 (First Summative Assessment) in the month of September  (Kendriya Vidyalayas have already started).  At this point, we found it would be useful to the students to have a set of sure shot questions. Practising these will essentially help you score better marks in the forthcoming exams.

 Portions for SA1

MOTION, FORCE AND WORK (Motion, Force and Newton’s Laws of motion, Gravitation)

Long Answer Type Questions

  1. Derive equations of uniformly accelerated motion using graphical representation of motion.
  2. Derive F=ma
  3. State the law of conservation of linear momentum. Illustrate with an example
  4. State and explain Archimedes’ principle.
  5. Describe an experiment to verify Archimedes’ principle.
  6. Distinguish density and relative density.
  7. What are the effects produced by force?
  8. What is friction? How is it caused? How can it be reduced?
  9. Define impulse of a force.
  10. Why does a cricket fielder pulls his hands backwards while taking a catch?
  11. Define inertia and explain its types with suitable examples.
  12. Describe two instances each where pressure is increased by decreasing the area and pressure is decreased by increasing hte area.
  13. State Newton’s universal law of gravitation
  14. Define G.
  15. Distinguish g and G
  16. Why motion and rest are said to be relative terms?
  17. Define acceleration due to gravity at a place and discuss its variation with height, depth and latitude.
  18. Write the differences between mass and weight.
  19. Can an object be accelerated if it is moving with constant speed? Justify your answer with an example
  20. Why is a person hurt more when he falls on a concrete floor than when he falls on a heap of sand from the same height?
  21. The weight of an object on the surface of moon is 1.67N and its mass on its surface is 1 kg. Calculate its weight and mass on the surface of earth, (g on earth = 10 m/s2).
  22. When a horse suddenly starts running, a careless rider falls backwards. Explain why?
  23. State the action and reaction in the swimming action of a swimmer.
  24. A stone is thrown vertically upwards with a velocity of 40 m/s and is caught back. Taking g=10 m/s2, calculate the maximum height reached by the stone.What is the net displacement and the total distance covered by the stone?
  25. Read more at:

    Read more at:


Summative Assessment 1 (SA1) Sample Papers for class 9 Physics

The Summative Assessment 1 is about to begin. As per request from student from various parts of India and abroad, we are publishing some solved sample papers in Physics, which we think, would help you in scoring better marks in the forthcoming SA1 exams.

india calcutta bookstore

(Based on Motion)


Class 9 Physics Sample Paper 1  Solved

Class 9 Physics Sample Paper 2  Solved

Post your blogs on Science related topics here

Hi Physics Fans!

We have enabled blogging by every member. Have an idea? You’re welcome to post’em here!

The posts will be published after scrutiny by admins. We prefer Science related articles, preferably Physics.

You can write on:

  • Latest news, events and happenings in the scientific world.
  • Promotional blogs on websites, institutions or persons
  • Create forums, Forum Topics and replies
  • … and anything else if it is related to the promotion of Physics!

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.

Must Practice Questions for CBSE Physics CLASS 12: Solved

We will publish here the portions one cannot afford to miss while preparing for the CBSE class 12  Physics Examination

The Chapters will be posted below. On Clicking the name of the chapter a new page will open. On that page there will be a set of collected questions. On clicking the questions, the complete solution to the questions will open.

Please note that this system is under preparation. We hope to complete this within a month. The link will be activated only after completing the project.



Where is electricity stored after it is generated but before it is supplied? (Chat Transcript from FaceBook)

Where is electricity stored after it is generated but before it is supplied?
    • Mahesh Sable Electrical power cannot be stored and,therefore,power plants must produce power as and when demanded.power stations r connected in parallel hence load is equally distributed,electric Power can be adjusted with help of step up or step down transformers.


    • Mathew Abraham Transformer does not increase power


    • Chitraja Rajan The demand for electricity varies randomly within a day itself…so there should be something which should be adjusted according to the demand.


    • Vishnu Mohan G huge capacitors? i think i read somewhere like this.


    • Rajat Sharma

      Hi All, the question is very smart, i think electricity stored before generation is stored in Water(DAM), Uranium Rods(Nuclear), HydroCarbons(Coal, GAS). Electricity can only store when it is in Direct Current format like in Batteries, Capacitor(its a very small time to store/release) Well there are many source where we can store electricity. When electricity is in demand then Power generation takes place within huge Alternators, this powers generation takes places in terms of Phase Shift between all the power Houses across the country, if this phase shift is disturb then power grid fails. after this the transformers come into picture so as to reduce Resistance loses.


    • Kannan Kannan Ps in my little knowledge electricity unable to store continuing process of generater get current


    • Chitraja Rajan at the generation side electricity is high ac current ..if it is converted into dc then there should be large containers to store them and also need suitable convertors to convert it in either form every time


    • Mathew Abraham In modern generators, there are equipment to control the rate of flow of water and in turn rate of rotation as well as the power generated. SO, it is quite right to say that electricity is generated as and when required. When you switch on a device power generation also increases until it reaches maximum capacity. Thereafter we will get less power. Remember the low voltage we suffer during the evening when the power consumption is maximum a few seconds ago · Like

You can also post your questions and answers and participate in discussions online at

Carbon Nanotubes to Store Solar Energy

MIT Researchers have developed a new solar thermal fuel that could store up to 10,000 times more energy than previous systems. The fuel consits os CNT modified with azobenzene. The finding is still in development stage.
Read more details at

Now have more fun at

Ask Physics is now more dynamic and Social Networking enabled. Members enjoy a lot of facilities like face book integration, making friends online, sending private messages, forums and groups and many more. Visit ask physics to find out the new additions and facilities.

Though anyone can ask a question and get the answers by email, joining the site as a member adds to the fun. Members can post questions directly to forums, join groups of their interest, like or unlike the posts and activities by other members, add members as friends, send messages to friends and a lot more are in the making.

Teachers can also join the site and start posting answers to the questions as well as taking part in online discussions at forums.

Future Plans

Ask Physics is planning to start a separate section for Physics Classroom Videos.