The diagram below shows a ray of light passing through two media.

When the wave travels from medium A into medium B, its speed

Question

The diagram below shows a ray of light passing through two media.

When the wave travels from medium A into medium B, its speed

BlackTom AI · Accepted Answer

The question asks about how the speed of a light wave changes when it moves from medium A into medium B, as shown by the diagram.
Option 1: remains the same. This would be true only if the two media had identical optical properties (refractive indices). Since the boundary is between two different media, their refractive indices are different, so the speed cannot remain unchanged. The diagram also shows refraction, which is a sign that speed changes.
Option 2: decreases. When light enters a medium with a higher refractive index (denser medium), its speed decreases. The diagram indicates the ray bends toward the normal upon entering medium B, which is a classic sign of slowing down in a denser medium. Thus this option matches the physical behavior.
Option 3: increases. An increase in speed would occur only if medium B had a lower refractive index than medium A (a less dense medium). The refraction toward the normal shown in the image contradicts this, since bending toward the normal is associated with reduced speed in the second medium, not increased speed.
In summary, the change in direction at the boundary (ray bending toward the normal) reflects a slower speed in medium B compared to medium A, consistent with the concept that light slows down when moving into a denser medium. Therefore, the correct interpretation is that the speed decreases when going from medium A into medium B.

The diagram below shows a ray of light passing through two media. When the wave travels from medium A into medium B, its speed

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