Final answer:
The oar appears bent when partially submerged in water because of refraction, where light bends as it moves from air to water.
Step-by-step explanation:
The reason an oar that is partially submerged in water appears bent is due to the phenomenon of refraction. Refraction occurs when light passes from one medium to another, changing speed and direction. Water has a higher index of refraction than air, which causes light rays to bend towards the normal (an imaginary line perpendicular to the surface) when entering the water. This bending of the path of light gives the illusion that the oar is bent at the point it enters the water.
Total internal reflection, while not the correct answer to this question, is another important optical phenomenon where light bounces back into the medium it came from rather than passing through to the next medium. This only occurs when the incident angle in the first medium is greater than the so-called critical angle for that pair of media. This principle is widely used in fiber optics and endoscopes for efficient light transmission.
Dispersion and specular reflection are not responsible for the apparent bending of the oar. Dispersion is the separation of light into its constituent colors, such as in a rainbow, and specular reflection is reflection from a smooth surface at a definite angle.