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The smallest particle visible to the naked eye is 40 microns. To give you some perspective, a piece of hair's width can range from 40 to 120 microns.
For the human eye, the visible radiations range from violet light, in which the shortest rays are about 380 nanometers, to red light, in which the longest rays are about 750 nanometers.. 380â750 nm. Human beings posses five senses, which include the ability to see, hear, taste smell and feel.