What causes the appearance of lines in a emission spectrum

The appearance of lines in an emission spectrum is caused by the fact that light is released as an electron moves to a lower energy state. When the atoms absorb energy they get excited and reach a higher level of energy. Then, when those atoms that are unstable release energy they pass to a lower level and emit light.

metric time was an attempt to create a standard unit of time based off of 10, but it never took off an is not included in the metric system (si)

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