The Physics of Waves: Light Waves, Sound Waves and Ultrasound

The violet end of the spectrum has waves of higher frequency than the red end; dim light refers to low amplitude light.

In fact both ultrasound and ultraviolet light have frequencies GREATER than infrasound and infrared light, respectively.

Essentially, a wave transfers energy without any matter moving away from its location.

The faster the red blood cells are moving, the greater will be the difference in frequency between the incoming and reflected ultrasound frequency. RBC move faster as they pass through a narrowing in a blood vessel. Ultrasound is inaudible, so you can’t hear the reflected ultrasound.

The impedance depends on the speed and density. Speed depends on the elasticity of the medium. So impedance is the more complete answer.

Prolonged exposure to 90 dB will result in hearing loss and so will 120 dB, but that will be noticeably painful.

The other choices also describe a wave but not in the most general terms.

Visible light are electromagnetic waves that are detectable by the human eye.

250 kHz is way above the upper limit of human hearing so is ultrasound.

The length of a wave is the distance between the two nearest points that are undergoing the same movement. This is happening at two adjacent troughs (or two adjacent crests too).