What is the effect called when light spreads out after passing through a narrow slit?

• A. Refraction
• B. Interference
• C. Reflection
• D. Diffraction

Answer: (D)

The correct answer is diffraction, which is the phenomenon that occurs when light waves encounter an obstacle, such as a narrow slit, and subsequently spread out. This behavior can be understood through the wave nature of light. When light waves pass through a narrow opening, they bend around the edges of the slit and spread out, creating a pattern of light and dark fringes as they interfere with one another.

Diffraction can be observed with various types of waves, but in the case of light, it is particularly noticeable when the width of the slit is comparable to the wavelength of the light being used. This spreading effect is characteristic of wave behavior, which is different from the straight-line propagation typical of light when it interacts with larger obstacles. Understanding diffraction is crucial in many areas of physics and engineering, including optics and telecommunications, as it explains how light behaves in real-world scenarios involving narrow spaces or openings.