Q&A

0. It takes 23 hours 56 min & a few seconds for earth to complete one rotation.Take it as 23hrs & 57 min.So there is a loss of 3 min daily in the watch or clock.But our watches and clocks are of 24 hrs(or 12*2). So after 240 days ther is a loss of 12 hours ie, when it is 12 noon actually the watch or clock will show 12 midnight yesterday.It is not happening.Why is it so?

It is because the earth also travels around the sun in its orbit. Hence, the time for the sun to go from exactly overhead to that position again is not the time it takes the earth to rotate once on its axis. The 3 minute difference makes sense: [(3 min lost per day)/(24x60 min/day)]x[365 days/year]=0.76 days lost per year, about three fourths. Hence, we need to add one day every fourth year to make it all come out right. Since it is not exactly 3/4 we do not add the extra day once each century.
1. 1. I have red that in troposphere temperature increases with height, then why doesn't the ice and snow in mountains melt?
Temperature decreases until about 20 km altitude, higher than any mountain. See Wikepedia for a graph of temperature in the troposphere.

2. Light is an electromagnetic wave, then why doesn't it get ionized in the ionosphere?
An electromagnetic wave has no electric charge, so how could it become ionized?


3.the rest mass of a photon is zero, it moves in the velocity of light.then according to einstein's equation m=m0/(sq:root of(1-v2/c2))& v=c so denominator will become 0 so it will have infinite mass.if it was happening we will die due to infinite mass on us when light fall on us.Why is it not happening?
Again we are dealing with E=mc2; if we consider a photon (which is a little bundle of light), it has energy. The shorter its wavelength, the more energy it has. For very energetic photons, called gamma-rays, their energy might exceed the mc2 energy of an electron plus a positron (the antiparticle of the electron, having the same mass but opposite charge as the electron). If this is the case, then it would not violate energy conservation if the photon suddenly turned into an electron-positron pair. For example, suppose that we have a 1.5 MeV (million electron volts, a unit of energy convenient for this kind of problem, look it up!) Now, the rest mass energy of an electron or positron is about mc2=0.5 MeV, so the photon could turn into a pair and that pair would have, in addition to their mc2 energy, about 0.5 MeV of kinetic energy. That is pair production. (By the way, this will not happen spontaneously because a photon is a stable particle; instead you must "tweak" it which is usually done by shooting the photons into a strong electric field like that near the nucleus of an atom.