The colour of light depends on

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ALP CBT 2 Electrician Previous Paper: Held on 22 Jan 2019 Shift 3

Answer 1

Visible light is the small part within the electromagnetic spectrum that human eyes are sensitive to and can detect.
The color of visible light depends on its wavelength and frequency.
Visible light waves consist of different wavelengths. These wavelengths range from 700 nm at the red end of the spectrum to 400 nm at the violet end.
Low-frequency radiation is invisible. With an adequately bright source of nearly 400 THz (1 THz = 10¹² Hz) most humans begin to recognize a dull red color.
As the frequency is increased, the recognized color gradually changes from red to orange to yellow to green to blue to violet. The eye doesn't recognize a violet color easily.
It always seems to look dark compared to other sources at equal intensity. Somewhere between 700 THz and 800 THz the world goes dark again.