Chapter 20 The Energy of Waves
The Nature of Waves A wave is any disturbance that transmits energy through a medium or empty space A disturbance is motion.
Waves Energy Energy is carried away from the energy source by waves. As waves travel away from their source they do work on everything in their path. Most waves transfer energy by the vibration of particles. This vibration is transferred from particle to particle. A medium is a substance through which waves travel. It may be a solid, a liquid, or a gas. Mechanical waves require a medium through which to travel. Electromagnetic waves (visible light, x ray, microwave, etc.) do not require a medium to travel.
Types of Waves-Transverse In a transverse wave the particles of the medium vibrate perpendicular to the direction the energy is moving. The highest point on a transverse wave is the crest. The lowest point is a trough All electromagnetic waves are transverse waves.
Types of Waves-Longitudinal In a longitudinal wave the particles of the medium vibrate parallel to the direction the energy is moving. The highest energy point on a longitudinal wave is a compression. Here the medium particles are very close together. The lowest energy point on a longitudinal wave is a rarefaction. Here the medium particles are very spread out. Sound is an example of a longitudinal wave.
Types of Waves-Surface Waves A surface wave forms whenever a transverse wave and a longitudinal wave combine. The particles in the medium of a surface wave move in circles. The particles move forward at the crest and backward at the trough. Only the energy is transferred by a wave. MATTER IS NEVER TRANSFERRED
Properties of waves are useful for comparing and describing waves.
Properties of Waves Amplitude-the maximum distance the particles of a wave vibrate from their resting positions. It is related to wave height. The greater the energy of the wave the greater the amplitude.
Properties of Waves Wavelength-the distance between 2 adjacent crests or troughs on a transverse wave and the distance between 2 adjacent compressions or rarefactions on a longitudinal wave.
Wave speed = wavelength x frequency Properties of Waves Frequency-the number of waves produced in a given amount of time. Units on frequency are hertz (Hz), 1 Hz = 1 wave/second. The greater the frequency the higher the energy. Wave speed-determined by the medium the wave is traveling through. Speed can be found with the following formula v=λ(f) Wave speed = wavelength x frequency High energy = short wavelength high amplitude high frequency Low energy = long wavelength low amplitude low frequency
Wave Interactions Wave interactions make it possible to observe certain events in our universe.
Reflection Reflection occurs whenever a wave bounces back after hitting a barrier. All types of waves can be reflected. Light waves reflecting off an object allows you to see that object even though it does not produce its own light. Light reflects best off of a smooth, light colored surface. Sound reflects best off of a smooth, hard surface. Reflected sound is called an echo.
Refraction Refraction is the bending of light as it passes from one medium to another. The 2 mediums have different densities so the wave’s speed, direction, and shape are affected. Refraction of the sun’s light after hitting a water drop in the atmosphere leads to the formation of a rainbow. The drop acts as a prism, which refracts the light by different amounts based on its wavelength. This causes the light to spread out into the rainbow shape.
Diffraction Diffraction is the bending of waves around a barrier or through an opening. The amount of diffraction by the wavelength and the size of the object causing the diffraction. You can hear sounds around a corner because sound has a longer wavelength and can bend around corners more easily than light.
Interference Interference is the result of 2 or more waves overlapping. Waves can occupy the same space and have an effect on one another. Types of interference Constructive-the crests of 2 waves overlap each other in such a way as to create higher crests and deeper troughs. This causes the new wave to have greater amplitude than the original waves. Destructive-the crest of one wave overlaps the trough of a second wave creating a wave with a smaller amplitude than the original waves. This can result in no wave at all.