Waves Study Guide

Ultrasound and infrasound are sound waves with frequencies beyond the range of human hearing. Ultrasound has frequencies above 20 kHz, while infrasound has frequencies below 20 Hz. Both have distinct applications due to their unique properties.

Ultrasound is widely used for imaging and ranging. In sonography (foetal scanning), high-frequency sound waves are emitted into the body; these waves reflect differently off tissues and organs, and the echoes are detected and used to form a real-time image of the foetus. This non-invasive method allows medical professionals to monitor foetal development and detect potential issues. Another major application is in Sonar (Sound Navigation and Ranging), used in marine navigation and mapping, where pulses of ultrasound are sent into the water. By measuring the time it takes for these pulses to return after reflecting off objects or the seabed, distances and underwater topography can be determined.

Infrasound, with its very long wavelengths, can travel significant distances and diffract around obstacles, making it useful for monitoring large-scale phenomena. For example, seismologists use naturally occurring infrasound generated by earthquakes, volcanoes, and meteor impacts to study the Earth's interior, including the Earth's core. By analysing how these low-frequency waves propagate through different layers, scientists gain insights into the composition and structure of the Earth, as well as detecting events over vast distances, even across continents. Infrasound is also used to monitor atmospheric events and nuclear tests.

Waves are fascinating phenomena that play a crucial role in transferring energy and information across vast distances. Unlike mass transit, waves accomplish this without physically moving matter from one point to another. Imagine a ripple spreading across a pond: the water molecules oscillate up and down, but they don't travel with the wave. The energy of the disturbance, however, clearly moves outwards. Similarly, sound waves transfer energy through the vibration of air particles, and electromagnetic waves, like light, transfer energy through oscillating electric and magnetic fields, all without transferring matter. This fundamental characteristic distinguishes wave motion from the bulk movement of objects.