Shadows and eclipse result from the

Analysis

The question asks for the fundamental principle of light that explains why shadows are formed and why eclipses (solar and lunar) occur.

Concept Explanation

The behavior of light is governed by several principles. To understand this question, we look at how light travels:

• Rectilinear Propagation of Light: This principle states that light travels in a straight line in a uniform medium. Because light cannot bend around corners or obstacles, when an opaque object is placed in the path of a light source, the light is blocked. The region behind the object where light cannot reach is what we perceive as a shadow.
• Eclipses: An eclipse is essentially a large-scale shadow. A solar eclipse occurs when the Moon passes between the Sun and the Earth, casting a shadow on the Earth. A lunar eclipse occurs when the Earth passes between the Sun and the Moon, casting a shadow on the Moon. Both phenomena rely entirely on the fact that light travels in straight lines and is blocked by these celestial bodies.

Step-by-Step Solution

1. Evaluate Option A (Reflection): Reflection involves light bouncing off a surface (like a mirror). While reflection creates images, it is not the cause of shadows.
2. Evaluate Option B (Rectilinear propagation): Since light travels in straight lines, it cannot "bend" around an opaque object. Therefore, the space behind the object remains dark, forming a shadow. This perfectly explains both shadows and eclipses.
3. Evaluate Option C (Diffraction): Diffraction is the bending of light around the edges of small obstacles or through small apertures. This is a wave property that usually causes light to spread out, not create sharp shadows.
4. Evaluate Option D (Refraction): Refraction is the bending of light as it passes from one medium to another (e.g., from air to glass). This is responsible for lenses and prisms, not shadows.

Conclusion

The formation of shadows and eclipses is a direct consequence of the fact that light travels in straight lines. Therefore, the correct principle is the rectilinear propagation of light.

Exam Tip: Whenever you see questions about "shadows," "pinhole cameras," or "eclipses," immediately associate them with the rectilinear propagation of light. These three are the classic JAMB examples for this concept!