The Physics
Hypertextbook
Opus in profectus

Interfaces and Barriers

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Discussion

interface

absorption

Sound, for example…

The characteristic acoustic impedance (specific acoustic impedance?)…

Z = ρv

is important when calculating the amount of reflection and transmission at an interface. For the reflected portion, notice that when Z2 < Z1, the sign of the reflected portion is negative, which indicates a change of phase.

R =  Z2 − Z1
Z2 + Z1
T =  2Z2
Z2 + Z1
reflected
pressure
amplitude		 transmitted
pressure
amplitude

obstacles and openings

Diffraction is the bending or spreading of light through an opening or around an obstacle.

Cartoon illustration of diffraction through three different sized openings and around three different sized obstacles

Goethe "flexibility of light"

Why is it possible to hear around corners, but not see around them?

Diffraction of laser light through a vertical opening of decreasing width. Note that as the opening gets narrower, the amount of diffraction in the horizontal direction increases. (The interference fringes will be dealt with in a later section of this book.) This image sequence is also available as an animated gif.
Single slit interference of a red laser through a small opening Single slit interference of a red laser through a small opening Single slit interference of a red laser through a small opening
Single slit interference of a red laser through a small opening Single slit interference of a red laser through a small opening Single slit interference of a red laser through a small opening