Superposition – constructive interference

∙Wave superposition is simply the addition of two or more waves passing simultaneously through a medium.
∙Superposition is also called interference and can be constructive or destructive, or anything in between.
∙Consider two in-phase pulses coming from each end of a taut rope.
∙The amplitudes x₀ of the two pulses add together, producing a momentary pulse of amplitude 2x₀.

 
Superposition – destructive interference

∙Wave superposition is simply the addition of two or more waves passing simultaneously through a medium.
∙Superposition is also called interference and can be constructive or destructive, or anything in between.
∙Consider two 180° out-of-phase pulses coming from each end of a taut rope.
∙The amplitudes x₀ of the two pulses cancel, producing a momentary pulse of amplitude 0.

Diffraction through a single-slit and around objects

∙If a wave meets a hole in a wall that is of comparable size to its wavelength, the wave will be bent through a process called diffraction.

∙If the aperture (hole, opening, etc.) is much larger than the wavelength, diffraction will be minimal to nonexistent.

FYI ∙

Diffraction is caused by objects within the medium that interact with the wave. It is not caused by two mediums and their boundary.

∙Christian Huygens explained the behavior of diffraction through his famous principle:
“Every point on a wavefront emits a spherical wavelet of the same velocity and wavelength as the original wave.”
∙Note that it is because of Huygen’s principle the waves can turn corners.
The reason waves can turn corners is that the incoming wave transmits a disturbance by causing the medium to vibrate.
∙And wherever the medium vibrates it becomes the center of a new wave front as illustrated to the right.

∙Note that the smaller the aperture b the more pronounced the diffraction effect.

FYI ∙

The aperture size must be of the order of a wavelength in order for diffraction to occur.