咩係wave同frequency?

光既wave係咩?

Light is electromagnetic wave (電磁波) in nature. It consists of changing electric and magnetic fields interacting with one another for the wave to travel forward.
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咁frequency又係d咩?

[Frequency] in general, is the number of repeating cycles (or events) in one second. If applies to light propagation, it is the number of changing electric, or magnetic, field cycle in one second.
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一條光wave有幾長代表d乜?

I presume you refer to the interpretation of the length of a [wavelength], as your original question doesn't make any sense.

The wavelngth of light dtermines its colour as appeared to our eyes. Red light has wavelngth longer than violet light, whereas the wavelength of yellow light is more or less at the middle of the visible spectrum.

A wave is a disturbance that propagates through space and time, usually with transference of energy. While a mechanical wave exists in a medium (which on deformation is capable of producing elastic restoring forces), waves of electromagnetic radiation (and probably gravitational radiation) can travel through vacuum, that is, without a medium. Waves travel and transfer energy from one point to another, often with little or no permanent displacement of the particles of the medium (that is, with little or no associated mass transport); instead there are oscillations around almost fixed positions.
圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/4/43/2006-01-14_Surface_waves.jpg/300px-2006-01-14_Surface_waves.jpg


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Surface waves in water
Frequency is a measure of the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency. The period is the duration of one cycle in a repeating event. So the period is the reciprocal of the frequency.
圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/6/6d/Sine_waves_different_frequencies.svg/360px-Sine_waves_different_frequencies.svg.png



圖片參考：http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png
Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above. The horizontal axis can represent for instance time or space.