Energy transformation at Dam

Light
Whether its source is the Sun, a flashlight, or a fluorescent bulb overhead, light is a form of energy that is common in our everyday lives. One of light's characteristic properties is that, in a transparent medium like air, glass, or still water, it travels in a straight line.

Light exhibits characteristics of both waves and particles, the latter of which are described as packets of energy called photons. These waves, or photons, travel in narrow beams called rays. Only when light rays move from one medium to another, such as from air to water, are their linear paths altered.

So how do we know that light travels in a straight line? Because of the nature of light—for example, it moves in a vacuum at a speed of more than 186,000 miles per second, or 300,000 kilometers per second—it is, for all practical purposes, impossible to observe individual particles. But evidence of its linear pathway can be seen in a number of demonstrations.

Wei Cong

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