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Relativity, Black Hole and some doubts

In the model of the big bang I would like to pose the following question. My understanding is that

1. The expansion of the universe is accelerating and

2. The radiation or shock wave to keep the analogy going is something we can measure.

My question is this. While we can rewind the clock to a single moment when the universe was infinity dense how do we know that this was a moment at all. Let me elaborate. As the universe expands could time or space time not also expand and if so than when the big bang occurred is something we cannot measure merely by rewinding the clock. If we are experiencing time at a given rate when the universe is at its current size would time not be being effected by the expansion also and if so would that mean the there was simply no start and no end to the universe? Perhaps the big bang is not as accurate as we may wish and perhaps it is our ability to comprehend that is limited. I propose there is no start or end to the universe it has always and will always be as it, and we, cannot exist without time and as such these two objects or things form a symbiotic relationship with each other. While the universe expands so does time and its effects are reduced in line with its expansion. Does this sound plausible and if not why?

A few selected questions fro CBSE Class 10 Physics Summative Assessment 1

Dear students,

If you are preparing for the CBSE Summative Assessment I for Class X, Give the following questions a try.


If you are not able to solve any of it, please post your doubts as comments to this post. The questions can be discussed here with due explanations.


Make it a practice to solve as much Sample papers and Guess papers as you can before writing the Board Exam.

All the best


  1. An electric geyser has the ratings 2000W, 220V marked on it. What should be the minimum rating in whole number of a fuse wire, that may be required for safe use with this geyser? (1Marks)
  2. Consider a circular loop of wire lying in the plane of a table. Let the current pass through the loop clockwise. Draw the direction of magnetic field inside and outside the loop. (2Marks)
  3. A wire is stretched so as to make its length double. What is the effect on its resistivity and why? (2Marks)
  4. Define electric power. Write its SI unit. What is the value of 1 kWh in joules. (2Marks)
  5. A torch bulb is rated 3.0V, and 600mA. Calculate its (i) power (ii) resistance (iii) energy consumed if this bulb is lighted for 4 hours.  (3Marks)
  6. (i) Differentiate between AC and DC giving two points of difference. (ii) What is the frequency of AC and DC in India? (iii) Draw a graph of current – time for AC and DC. (3Marks)
  7. Name and state the law which relates the potential difference in a circuit to the magnitude of current that flows through it. Give its mathematical expression and draw the theoretical graph too. (3Marks)
  8. What is electromagnetic induction? State Fleming’s Right Hand Rule. A coil of copper wire is connected to a galvanometer. What would happen if a bar magnet is (a) pushed into the coil with north pole entering first? (b) pulled out of the bar magnet? (c) held stationary inside the coil?
  9. State Joule’s law of heating. How does the electric fuse prevent fires due to shortcircuit or overloading? A household uses the following electric appliances. (i) Refrigerator of rating 400W for ten hours each day. (ii) two electric fans of rating 80W each for twelve hours each day. (iii) six electric tubes of rating 18W each for six hours each day. Calculate the electricity bill of the household for the month of June if the cost per unit of electric energy is Rs. 3.00. (5Marks)

Which books should be referred for IIT JEE ?

We have received hundreds of questions on the above subject. As the questions continue to pour in, we found it necessary to create a post on it.

IIT JEE is an entrance exam of international repute and IITs are considered at par with MIT by many. So, if you are an IIT aspirant, it is very much essential to prepare well in advance.

In this article we are focusing on Physics only

Know the fundamentals

Knowing the fundamentals is the first step. Learn your daily lessons well. In learning Physics, “Questioning Every Answer is more important than Answering Every Question”

Whenever you learn a new concept, try to get all the doubts clarified. Ask doubts and questions to your teachers. (If they don’t answer you satisfactorily, post them at www.askphysics.com )

Observe your surrounding and try finding examples on what you have learnt. The syllabus and books give you a framework on what to study; but don’t just limit your studies on books and syllabus. Search related information from real life and other sources of reference.


The very first book you cannot avoid is the NCERT TEXT BOOK for class XI and XII

These books are designed after thorough research and the exercises are carefully added. Be sure to solve all the exercises including the Additional Exercises

Here are some of the Books you can refer for practicing for IIT JEE

  1. Concepts of Physics (by H C Verma)
  2. Fundamentals of Physics (by Resnick, Hallidey)
  3. University Physics (Zemansky)
  4. Problems in Physics (IE Irodov)


By the by, having too much books will be a hindrance. It is better to start with the NCERT books and after mastering all the exercises take up Resnick Hallidey and after clarifying the concepts take up Problems from H C Verma’s concepts of Physics and then go on to IRODOV if time allows.

Wish you all the best.

Electromagnetic Waves :: Doubts continue …

Siva Sai asked:

why are oscillating electric and magnetic feilds created when an elctromagnetic wave is travelling?


[wiki]Electromagnetic waves[/wiki] are produced by mutually perpendicular time varying electric and magnetic field mutually reinforcing each other.

EM Wave

Magnetic Field of Earth

RS asks:

“could u please explain me what is earth’s [wiki]magnetic field[/wiki]? in detail and easily in brief?”


Please refer to http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magearth.html for details. If you have any specific doubts related to it please ask as comment here.

Also see http://en.wikipedia.org/wiki/Earth’s_magnetic_field


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