Addiction: Central nervous system (CNS) stimulants are addictive, even if they are not abused. Many factors, including the patient's personal history, the type of stimulant that is being taken, the dose of the drug, and duration of use, influence how likely an individual is to become addicted.
The source of all waves - mechanical or electromagnetic - is something that is vibrating. Matthew Donovan.
The end result of refraction comes from phase matching at media interfaces, which comes from boundary conditions. I will begin with the assumptions that come from observation. I start with a set of 3 plane waves -- an incident one, coming in at an angle, a reflected one, and a transmitted one.