Differences in impedance between media cause which phenomenon at boundaries?

• A. Attenuation
• B. Reflection At Boundaries
• C. Refraction
• D. Diffraction

Answer: (B)

Impedance mismatch at a boundary causes waves to reflect. When a wave moves from one medium into another with a different impedance, the boundary conditions that govern how the wave can pass through can’t be satisfied perfectly by transmission alone, so part of the wave energy bounces back into the original medium. The stronger the impedance difference, the more energy is reflected (for normal incidence, the reflection scales with (Z2 − Z1)/(Z2 + Z1)). If the impedances were the same, there would be little to no reflection and the wave would transmit with a change in speed. Refraction is the bending of the transmitted wave due to the speed change in the new medium, while attenuation is loss of energy to absorption, and diffraction is bending around obstacles; these are not the direct consequence of impedance differences at a boundary.