<span>Refraction happens when there</span> is a bending of path of a light wave as it
passes across the boundary separating two media and the degree of bending is
determined in part by the total change in velocity as the light<span> passes from one medium to the other. In
addition, the change in speed experienced by a
wave when it changes medium can result in a number of beautiful optical effects. </span>
High-residue cover cropping is an adaption of conservation tillage in which a high-biomass cover crop is grown during the winter and is rolled or cut down prior to no-till or strip-till planting in spring.
Chemical factors: This is due to internal stimuli. Changes in the blood such as decrease in O2, increase in CO2 and decrease in PH cause impulse in the carotid artery which stimulates the respiratory centers in the medulla and cause breathing.
Mechanical factors: also called external stimuli. Compression of the fetal chest during delivery forces small amount of lung fluid out of the lungs. This increase in pressure in the chest draws air into the lungs.
