Final answer:
Total internal reflection (option 4) can result in radar holes or blind spots by reflecting waves entirely back into the medium when the incident angle exceeds the critical angle, as opposed to being refracted out of the medium.
Step-by-step explanation:
The form of refraction that may result in radar holes or blind spots is total internal reflection. This phenomenon occurs when the incident angle of a wave such as radio waves in the case of radar, exceeds the critical angle. At this point, instead of being refracted out of the medium, the wave is reflected entirely back into the medium, potentially creating areas where the radar cannot detect objects, known as radar holes or blind spots.
The critical angle is the smallest angle of incidence at which total internal reflection occurs, and it depends on the indices of refraction between the two different media involved. For example, in optical fibers used in telecommunications, light is trapped within the fiber by this principle, ensuring the light signal travels long distances with minimal loss.