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    AskPhysics Blog Feed Dear students, CBSE has given you more time for exams. We have approximately 7 days before the Physics exams. How to use this seven days effectively for a thorough revision is very important. 7-8 days of sleeping is a must. One hour of exercise 1 to 2 hours for break fast lunch […]
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    AskPhysics Blog Feed Doubt from AskPhysics.comI have heard the following statements-> 1. Quarks always exist in a group of 2 or 3, and can not stand alone. 2. Protons are made up of 2 up quarks, and 1 down quark. 3. Quantum mechanics allows us to entangle a particle by somehow dividing it into 2(For […]
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    AskPhysics Blog Feed The basic concepts of relativity are explained in a very simplified way that are easy to understood by Mr. Vivek Sawhney in this YouTube Video… The video focuses upon the general discussion on Theory of Relativity….What is the theory of Relativity? What is time dilation and length contraction? SUBSCRIBE to the YouTube […]
  • A numerical problem from motion in 1 Dimension
    AskPhysics Blog Feed A boy plays with a ball on a field surrounded by a fence which has a height of 2.5m . He kicks the ball vertically up from a height of 0.4m with a speed of 14 ms−1. (a) What is the maximum height of the ball above the fence? (b) What is […]

Great Physicists – A SlideShow

Which way is better for giving AIEEE exam? ONLINE or OFFLINE.

Which way is better for giving AIEEE exam? ONLINE or OFFLINE.

-Yash asked –


I would personally recommend online. But the choice is up to you.

Please follow the following check to decide. Try to identify for yourself the plus points and negative points of writing AIEEE online and OFFLINE.

The most important disadvantage of choosing the OFFLINE version is the rarity of choices. You may have to travel long if you are not nearby the centre.

The decision is yours. But, think well before you decide.

Atoms and Nuclei – PowerPoint Presentation

Does gravity travel instantaneously?

Does gravity travels instantaneously? Or it travels equal to the speed of light.


No clear answer now. If we believe in the Theory of relativity, Gravity (Gravitational Waves travel with the same speed as that of light in vacuum. If gravitons are like photons, then it makes sense too.

However I invite you to think more and post your thoughts as comments here. Let the discussion begin.

I found the following links to know more

  • http://metaresearch.org/cosmology/speed_of_gravity.asp
  • http://en.wikipedia.org/wiki/Speed_of_gravity
  • http://www.desy.de/user/projects/Physics/Relativity/GR/grav_speed.html

Numerical Problems From Optics

  1. When an object of height 4cm is placed at 40cm from a mirror the mirror forms the image on the object itself. If the height of the image is equal to the height of the object. Find out the focal length of the mirror and identify the mirror.
  2. A convergent beam of light passes through a diverging lens of focal length 0.2m and comes to focus at distance 0.3m behind the lens.Find the position of the point at which the beam would converge in the absence of lens?

Speed of sound

Why sound travels faster in humid air than normal air as humid air is denser than normal air? (Akash asked)


The speed of sound in a medium is inversely proportional to the square root of its density. Humid air is less dense than dry air. Therefore the speed of sounf in humid air is greater than that in dry air.


Are you thinking why dry air is more than that of humid air? This is a common misconception. Students used to think that humid air is denser than dry air. But it is not so. Just like skimmed milk (milk removed off its cream) is more dense than normal milk (with cream). Density of cream is much less than that of the rest of milk. So when it is removed, the residual milk becomes denser.

Humid air contains water vapor content. Water vapor is lighter than air. So when air contains water vapor, its density is less. When the water content is removed, it becomes denser.

For more details refer:

What is present in between the atoms of gases?

What is present in between the atoms of gases?

(Aniket Mukherjee asks)

Answer: Nothing. Vacuum

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