A narrow beam of microwaves travels from air directly into a block of styrofoam of…
PHYSICS · Single correct · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics
Problem
A narrow beam of microwaves travels from air directly into a block of styrofoam of the same temperature. Nearly all of the microwave energy continues forward, and virtually none is reflected back into the air. Which statement best accounts for this observation?
(a) Microwaves have a wavelength much larger than the boundary thickness, so they pass through without reflection.
(b) The speed of microwaves is essentially the same in air and styrofoam, eliminating any reflection.
(c) The two media have nearly the same wave impedance, so very little energy is reflected.
(d) The electric field of the microwaves cannot induce currents in an insulator, so reflection cannot occur at the styrofoam surface.