Understanding Diffraction and Interference

"As is true for all waves, light travels in straight lines and acts like a ray when it interacts with objects several times as large as its wavelength. However, when it interacts with smaller objects, it displays its wave characteristics prominently. Interference is the identifying behavior of a wave." "**Huygens's principle** states, 'Every point on a wavefront is a source of wavelets that spread out in the forward direction at the same speed as the wave itself. The new wavefront is a line tangent to all of the wavelets.'" "The bending of a wave around the edges of an opening or an obstacle is called **diffraction**. Diffraction is a wave characteristic that occurs for all types of waves." "To obtain constructive interference for a double slit, the path-length difference must be an integral multiple of the wavelength, or $d \sin\theta = m\lambda$, for $m = 0, 1, -1, 2, -2, \ldots$ (constructive)." "Similarly, to obtain destructive interference for a double slit, the path-length difference must be a half-integral multiple of the wavelength, or $d \sin\theta = (m + \tfrac{1}{2})\lambda$."