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Monthly Archives: May 2011


A Question From Relativity

Sreeram Asks:

“my question is on relativity.Let us say two persons,one is standing still and other is moving with uniform velocity in a straight line(in +ve x direction),both are carrying  a clock synchronized previously.For the moving person he is at rest and the other guy is moving away from him in the opposite direction(negative x direction).Both of them feel that clock of the other guy is moving slowly.let us say the moving guy never stops and he calls the other in telephone at some point of time and asks the
time in his clock.But he will find that clock with him,is actually faster.how can that happen?”


Please note that the theory of relativity can  be applied only for velocities compared to that of light in vacuum (3 lakh km/s). The situation will be very much different when we travel at such velocities. So far we are able to accelerate only subatomic particles to this speeds (LHC).



Why don’t we get a shock when we step out of house?

the top of the atmosphere is at about 400kv with respect to surface of the earth,corresponding to an electric field that decreases with altitude. near surface of the earth the field is about 100v/m. why then do we not get an electric shock as we step out of our house into open?

Acceleration of a jet plane

Chin Reyes asks:

what acceleration (in meter per square second) is experienced by the passenger in a jet airplane making a level turn of radius 1km at a speed of 400km/hr ?


Answer to be posted soon

How does light travel?

Akashjot Kaur asks

“how a wave travels ? eg. light has dual nature ,since  light consists of particles ,and in the wave character we say it moves in the form of electric & magnetic perpendicular wave.how is it possible? it travels in the form of waves or particles?”

Answer to be posted soon

The person in a Portrait always looks at me?!

Kunal Asks:

“when we look continuously into the eyes of a person in a photo frame and change our position then the person appears to follow us.why is it so?”


Ans: Because the portrait is inanimate and is drawn in such a way that it is looking at the spectator. So, it will seem to be looking at you when you look at it. But this will not happen in the case of a statue.

Why Electric Current is a Scalar Quantity?

Vaishali asks:

“Why is current a scalar quantity even after having both magnitude as well as direction?”



For a physical quantity to be termed a vector quantity, having magnitude and direction is not enough. The quantity should obey the laws of vector addition too. Like the triangle law or the parallelogram law. As we know, if two currents meet at a junction, the total current of the resultant current will be the algebraic sum of the two current and not the vector sum.


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