Final answer:
The phenomenon where the direction of a light ray changes as it passes from one medium to another is known as refraction, which occurs because of variations in the speed of light in different media. Option B) Reflection is the correct answer.
Step-by-step explanation:
The changing of a light ray's direction as it passes from one medium to another is a fundamental concept in physics known as refraction. This phenomenon occurs when light enters a medium with a different refractive index, causing it to bend. Snell's Law describes how the angle of incidence and the angle of refraction are related to the indices of refraction of the two media. The degree to which light bends depends on the difference in the speed of light in each medium and is quantitatively expressed by the refractive indices.
For example, when light travels from air into water, it slows down due to water's higher refractive index. This results in the light ray bending towards the normal—a line perpendicular to the boundary between the two media. Conversely, when light exits water into air, it speeds up and bends away from the normal. These changes in direction are responsible for various optical effects such as the apparent bending of a straw placed in a glass of water or the focusing power of lenses.
The correct option for the question, 'The direction of a light ray changes as it passes from one medium to another. The phenomenon is called?' is B) Reflection.