Question

Wavelength of visible light/PAR is
A. 200-400 nm
B. 400-700 nm
C. 700-800 nm
D. 100-200 nm

Answer 1

A light spectrum is the range of wavelengths under which lights of different wavelengths fall. They may or may not be visible to us. They are measured in nanometers (nm). We can detect objects under a particular range only.

Complete answer:
The objects whether colourful or black and white are visible to us due to the light which falls on them to make them visible. The light reflects from the objects making them visible. This visible range for humans is different from some other animals. We have sight only in a particular range of the light spectrum.

Option A: 200-400 nm: The Ultraviolet light is visible under this range of wavelength. UV rays are harmful to nature.

Option B: 400-700 nm: The visible light under which we can see things in surrounding fall under the visible range of the spectrum. The wavelength of this light is 400-700 nm. The various colours are differentiated and seen under this range.

Option C: 700-800 nm: Above the 700 range, there are Infrared rays. They are invisible to human eyes. They lie above the human visible range of light. These are the electromagnetic radiations.

Option D: 100-200 nm: This range also includes the non-linear UV range, combination of gases. This is particularly a range of vacuum ultraviolet bands.

Hence, the correct answer is option (B).

Note: The colours visible to us in the visible range are red, orange, yellow, green, blue, violet. These all the lights fall under the electromagnetic spectrum, which also includes X rays, Gamma rays, Optical rays etc.