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# Tag Archives: information

## Space Time

What is space time?

Ans:

In order to describe an event, we need to specify its position in space and the time of occurrence. A four-dimensional continuum with the three co ordinates of space and time as the fourth co ordinate is called space-time.

Can you say What’s This?

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## Concept of magnetic dipoles

“Can u explain Concept of magnetic dipoles” – Sam Asked

Answer: A magnet always exist in pairs. A magnetic dipole consists of two equal and opposite poles separated by a small distance. The magnetic poles cannot exist alone. Monopoles does not exist.

A single current carrying loop is a simple practical  example for a magnetic dipole.

## Propagation of Light, Group velocity and Phase velocity

“how can light travel in the form of waves in space, which has no medium? if light doesn’t travel in the form of wave in the space then in equation. ‘phase velocity=c^2/group velocity ‘ phase velocity becomes zero and also c=0, which indicates velocity of light =0, but light actually travel in space . How can this be possible?”

I feel that there is some sort of misunderstanding in your concept.

Why should phase velocity become zero?

Please remember that light is an electromagnetic wave, where the propagation is due to the mutually reinforcing time varying electric and magnetic field vectors varying in mutually perpendicular directions.

The phase velocity is a the speed at which a point of fixed phase (say the crust of the wave)  propagates, which is not always the speed at which the electromagnetic information travels.

Group velocity is the speed at which electromagnetic information travels.

## Physics and Mobile Phones

“Where is physics in mobile other than circuits?”

A mobile phone uses Physics throughout its functioning as well as the communication techniques involved.”

http://www.yale.edu/ynhti/curriculum/units/2003/4/03.04.07.x.html

http://www.phys.soton.ac.uk/outreach/files/Mobile%20Phone%20Activities%20Sheet.pdf

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