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V proportional to I or I proportional to V in Ohm’s Law?

Why we used I proportional to V?
Can we write V proportional to I also?



Both are ok. If we are changing the current and observing the voltage, then it is V∝ I

If we are changing the voltage and observing the current, then

I∝ V

In general, we write

the dependent variable proportional to the independent variable

dependent variable  = the quantity measured by us

independent variable = the quantity fixed by us

Speed of Light or Velocity of Light?

Why do we say speed of light,instead of velocity of light?.can we say that also?

Asked Abdur Rahman


When direction is of no relevance, it is better to say speed of light.

Why does the sun appear to rise and set though it is actually not moving?

Why does the sun appear to rise and set though it is actually not moving?

Shivangi asks


English: Animated image of Earth rotating.

First of all I would like to remind you that it is incorrect to say that “sun is not moving”. Sun is also moving. But the question here is, “Sun appears to rise and set not because of its motion”.

Sunset and sunrise are caused by the rotation of earth. When earth rotates, the position of sun appears to change and it seems as if the sun is revolving around the earth; just like we feel that the ground is revolving around us when we are looking out from a rotating merry-go-round.

Why are you hurt more when you punch a wall then when you punch a sponge?

Why are  you hurt more when you punch a wall then when you punch a sponge?

Asked Shivangi


This is explained on the basis of impulse momentum principle.

Impulse of a force is the product of Force and time and is equal to the change in momentum produced.

The overall effect of a force is the change in momentum produced.

When we are punching, the effect on hitting is the stopping of the fist moving initially with a particular speed.

So, if we hit on a wall, the change in momentum takes place in a small interval of time and therefore the average force involved is very large and therefore it hurts.

When we hit on a sponge, the time taken will be more and the average force will be less and therefore it hurts less.

why an athlete continuous his motion after reaching its finish line?

why an  athlete continuous his motion after reaching its finish line?

Asked Shivangi


This is a consequence of inertia of motion. When the athlete reaches the finishing line, he will be at a high speed. Due to inertia he continues his motion

Supercomputer to unravel the Cosmos!

In a one-of-its-kind invention, celebrated theoretical physicist Professor Stephen Hawking has launched the most powerful shared-memory supercomputer in Europe christened Cosmos. Produced by Silicon Graphics Inc, this supercomputer is expected to unravel the mysteries of the Universe. Flexible in nature, its shared-memory system will not only develop researchers’ capabilities across the United Kingdom but will also ensure their leadership in cosmological research at the international level.

Special Theory of Relativity

Could you please explain me that why can’t we use inverse Lorentz transformation to prove length contraction in the case of two frames that are in relative motion with each other. I could derive the relation by using Lorentz transformation but not through inverse Lorentz transformation. Its exactly opposite in the case of time dilation. There we are supposed to use inverse Lorentz transformation and not Lorentz transformation. Why is it so?
(Gamini asked)

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