The correct option is 2 only
Explanation
Diffraction is a wave phenomenon where light bends around the corners of an obstacle or spreads out after passing through an aperture. This effect becomes significant when the size of the obstacle or aperture is comparable to the wavelength of the light.
Statement-wise Analysis:
- Statement 1 is Incorrect: When an opaque object on the path of light is very small (comparable to the wavelength of light), light does not strictly follow a straight line but bends around the edges of the object. This bending of light is the defining characteristic of diffraction.
- Statement 2 is Correct: The straight-line treatment of light rays (rectilinear propagation) is the fundamental assumption of Ray Optics (Geometrical Optics). This assumption holds true only when the obstacle size is much larger than the wavelength of light. When diffraction occurs, the ray model fails to explain the bending of light, and Wave Optics must be employed. Therefore, the straight-line treatment does not remain valid in this context.
Key Takeaway: Diffraction sets a limit on the validity of ray optics. When obstacles are minute, light behaves as a wave rather than a ray, causing it to encroach into the shadow region.