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Kim Wilzon Grade: 12

Define Visible Light

7 years ago

Answers : (1)

Sachin Tyagi
31 Points

We may operationally define visible light to be electromagnetic radiation to which the eye is sensitive. The sensitivities of individual observers may vary, but humans can typically observe radiation with wavelengths from 400 nm to 700 nm. Within that range, the sensitivity to different wavelengths is not at all constant.

Figure shows a representation of the variation in the sensitivity of an average human observer to radiations of differing wavelength but constant radiant intensity over the visible region of the spectrum. The greatest sensitivity occurs near 555 nm, corresponding to light of a yellow green color. The sensitivity decreases rapidly at both long and short wave lengths; we can roughly set the limits of the visible region, where the sensitivity is equal to 1% of that of the peak, to be 430 nm and 690 nm. Source of visible light depend ultimately on the motion of electrons. Electrons in atoms can be raised from their lowest energy state to higher states by various means, such as by heating the substance or by passing an electric current through it. When the electrons eventually drop back to their lowest levels, the toms emit radiation that may be in the visible region of the spectrum. Emission of visible light is particularly likely when the outer electrons are the ones making the transitions.

The most familiar source of visible light is the Sun. its surface emits radiation across the entire electromagnetic spectrum, but it’s most intense radiation is in the region we define as visible, and the sun’s radiant intensity peaks at a wavelength of about 550 nm, corresponding precisely to the peak in the sensitivity of the average human observer. This suggests that, through natural selection, our eyes evolved in such a way that their sensitivity matched the sun’s spectrum.

7 years ago
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