The blood in the pulmonary artery is violet because it is not oxygenated, while the blood carried by the pulmonary veins is oxygenated and its color is scarlet.
Explanation:
Under normal conditions, the arteries carry oxygenated blood, giving it a dazzling red or scarlet color, while the veins carry non-oxygenated blood —called venous blood— of a purplish and dark red color.
The only exceptions are the pulmonary arteries and veins
<u><em>Pulmonary arteries</em></u><em> carry non-oxygenated blood from the right ventricle to the lungs. They are the only arteries that carry non-oxygenated blood.</em>
<u><em>Pulmonary veins</em></u><em> carry oxygenated blood from the lungs to the left atrium, being the only veins to carry blood with oxygen.</em>
<u>This is why in the pulmonary arteries the blood is violet, and in the pulmonary veins the blood is scarlet</u>.
Electromagnetic waves all travel at the speed of light when in vacuum, and essentially this same speed in normal air. Since wave speed is product of frequency and wavelength, c = f λ and λ = c/f = (3.00 x 108 m/s) / (7.5 x 1014 Hz) = 4.00 x 10-7 m = 400 x 10-9 m = 400 nm.
