physics....

There are various kinds of forces, strong and weak. For example, gravitational force, electromagnetic force, nuclear force. Eienstein first mooted the idea that the origin of all these forces are the same and tried to formulate a theory which will support this .In other words he tried to unify all the forces into a single entity.

thank u very much 4 that
but who has introduced this theory

anybody pleazz tell me
1.why the clouds appear black when the rain is about to happen?
2. why the candle light always acquires that particular shape when glowing and why its color changes gradually as the wax melts?

thanks arka but what about d second ques????

Sorry ... Gaurav ... don't know the reason .... still I'll try to find out ...

i think ,when raining the clouds entirely cover the surrounding sky at that position not allowing suns rays and it appears to be black (dim)

There are two things going on to make some rain clouds to appear very dark. The first is that some clouds, especially thunderstorm clouds such as nimbocumulus clouds can tower to great heights with tops 15 to 20 km (50-60 thousand feet) above the earth. Plus these clouds, which tend to produce very heavy rains and hail are very dense, being full of water vapor and raindrops at lower altitudes and ice crystals at high altitude.

As a result, it is more difficult for sunlight to pass through these clouds than it is for light to pass through neighboring clouds which aren't as high and dense. More of the light is reflected back into space or sideways because there's more obstacles. Plus, there's more absorption of the light on its way through the cloud, because the light will bounce around very much and take a very long total path before finally coming out the bottom of the cloud.

The second effect which enhances our perception of a dark cloud has to do with how the human eye and brain perceive light and color. We don't judge brightenss and color very accurately in an absolute sense; rather, our perception of one part of a scene is affected by what else is going on in the scene. For example, think about how a television screen looks like when the set is turned off: the screen is a medium dark gray. Yet, when the set is turned on, parts of the picture can look quite black. But the reality is that what we perceive as "black" is really this medium dark grey color. (The picture tube can only add light, it can't "suck out" light!) This phenomenon of color perception is called "chromatic induction" and is the basis of some optical illusions..

A similar thing is going on with the clouds: a region of the sky is darker because less light is passing through the cloud, but we perceive the cloud to be even darker and blacker than it is because it's surrounded by brighter clouds.