(WVS) Wave Interactions Lesson

Wave Interactions

Waves interact with matter in several different ways that we will explore in this lesson. The interactions could occur when waves pass from one medium to another, bounce back like an echo, bend or spread out around or through edges, or come in direct contact with each other. These ways that waves may interact with matter are called reflection, refraction, diffraction, and interference. Each type of interaction is described in detail below.

Reflection

Reflection occurs when waves bounce back from a barrier they cannot pass through. Reflection can happen with any type of wave, not just sound waves. For example, reflection can be seen when ocean waves hit a rocky coast. Light waves are also reflected and that's how we see most objects. Light from a light source, such as the sun or a light bulb, shines on the object, and some of the light is reflected. When the reflected light enters our eyes, we can see the object.

Reflected waves have the same speed and frequency as the original waves before they were reflected. However, the direction of the reflected waves is different. When waves strike an obstacle head-on, the reflected waves bounce straight back in the direction they came from. When waves strike an obstacle at any other angle, they bounce back at the same angle but in a different direction. Very smooth surfaces such as mirrors reflect almost all incoming light.

Ships on the ocean make use of the reflecting properties of sound waves to determine the depth of the ocean. A sound wave is transmitted and bounces off the seabed. Because the speed of sound is known and the time lapse between sending and receiving the sound can be measured, the distance from the ship to the bottom of the ocean can be determined. This is called sonar, which is an acronym for Sound Navigation And Ranging.

Animals, like dolphins and bats, make use of sound waves to find their way. Just like ships on the ocean, bats use sonar to navigate. Waves that are sent out are reflected off the objects around the animal. Bats, or dolphins, then use the reflected sounds to form a "picture" of their surroundings. This is called echolocation.

An adaptation of sonar is used to create images of structures inside the human body - this is called medical ultrasound. Ultrasound is very high-frequency acoustic energy, much higher than the frequency range audible to humans. This high frequency means that the patient is not disturbed by the noise, and high amplitudes can be used, but primarily ultrasound is chosen because high-frequency sounds have small wavelengths. This small wavelength allows a very high degree of image detail to be recorded.

'Stealth' devices are those that attempt to make an object non-reflective - if the waves do not bounce off your aircraft, then no one will know it is there!   In a way, glass is a 'stealth' technology - light waves pass through it, and if it is very clean we may walk straight into it before realizing that it is there!

[CC BY 4.0] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION