Properties of waves

the energy in the waves spreads out over a larger area. 2. this is why large speakers and amplifiers are need to fill a concert hall. VI. Vibrations and Waves i. when a singer sings a note, the vocal cords in the singer’s throat move back and forth. a. that motion makes the air in the throat vibrate, creating sound waves that eventually reach your ears. b. The vibration of the air in your ears causes your eardrums to vibrate 1. the motion the eardrum triggers a series of electrical pulses to your brain, and your brain interprets them as sounds. ii. most waves are caused by a vibrating object. c. Electromagnetic waves may be caused by vibrating particles d. In a mechanical wave, the particles in the medium also vibrate as the wave passes through the medium. VII. Vibrations involve transformations of energy i. refer to page 359 for the diagram and description for this section VIII. A wave can pass through a series of vibrating objects. i. refer to page 361 for the diagram and description for this section IX. The motion of particles in a medium is like the motion of masses on springs. i. if you tie one end of a rope to a doorknob, pull it straight, and then rapidly move your hand up and down once, you will generate a single wave along the rope. a. A small ribbon tied in the middle of the rope would help visualize this ii. as the wave approaches, the ribbon moves up in the air, away fro its resting position.(crest) iii. as the rope goes past the ribbon, in sinks down past its original resting position(trough) iv. The motion of each part of the rope is like the vibrating motion of a mass hanging on a spring. a. As one part of the rope moves up and down, it pulls on the part next to it, transferring energy. 1. in this way, a wave passes along the length of the rope X. Transverse and Longitudinal waves i. particles in a medium can vibrate either up and down or back and forth. ii. waves are often classified by the direction that the particles in the medium move as a wave passes by XI. Transverse waves have perpendicular motion. i. in the rope and door knob example, each particle in the rope moves straight up and down as the wave passes by from left to right a. in theses cases, the motion of the particles in the rope, is perpendicular to the motion of the wave as a whole b. waves in which the motion of the particles is perpendicular to the motion of the wave as a whole are called transverse waves 1. Transverse waves- a wave that causes the particles of the medium to vibrate perpendicularly to the direction the wave travels ii. Light waves are another example of transverse waves. a. The light fluctuations in the electric and magnetic fields that make up a light wave are perpendicular to the direction the light travels XII. Longitudinal waves have parallel motion i. suppose you stretch out a long, flexible spring on a table or a smooth floor, grab one end, and move your hand back and forth, directly toward and directly away from the o other end of the spring. a. you would see a wave travel along the spring as it bunches up in some spots and stretches in others. ii. As a wave passes along the spring, a ribbon tied to one of the coils of the spring will move back and forth, parallel to the direction that the wave travels. a. waves that cause the particles in a medium to vibrate parallel to the direction of wave motion are called longitudinal waves. 1. sound waves are an example of longitudinal waves that we encounter every day 2. sound waves traveling in air compress and expand the air in bands 3. as sound waves pass by molecules in the air move backward and forward parallel to the direction that the sound travels XIII. In a surface wave, particles move in circles i. waves on the ocean or in a swimming pool are not simply transverse waves or longitudinal waves. a. water waves are an example of surface waves. b. surface waves occur at the boundary between two different mediums, such as between water and air. c. the particles in a surface wave move both perpendicularly and parallel to the direction that the wave travels. XIV. Wave Properties. i. all transverse waves have somewhat similar shapes, no matter how big they are or what medium they travel through. a. an ideal transverse wave has the shape of a sine curve. 1. sine curves can be used to represent waves and to describe their properties ii. waves that have the shape of a sine curve, such as those in the rope example, are called sine waves. a. although many waves, such as water waves, are not ideal sine waves, they can still be modeled with e the graph of a sine curve. XV. Amplitude measures the amount of particle vibration i. the highest points of a transverse wave are called crests ii. the lowest parts of a transverse wave are called troughs. iii. the greatest distance that particles are displaced from their normal resting positions because of a wave is called the amplitude. a. the amplitude is also half the vertical distance between a crest and a trough b. larger waves have bigger amplitudes and carry more energy iv. Longitudinal waves do not have crests and troughs because they cause particles to move back and forth instead of up and down a. if you make a longitudinal wave in a spring, you will see a moving pattern of areas where the coils are bunched up alternating with areas where the coils are stretched out 1. the crowded areas are called compressions 2. the stretched out areas are called rarefactions XVI. Wavelength measures the distance between two equivalent parts of a wave i. the distance from one crest of a wave to the next crest, or f room one trough to the next trough is called the wavelength. a. in a longitudinal wave, the wavelength is the distance between two compressions or between two rarefactions. b. The wave length is the measure of the distance between any two successive identical parts of a wave 1. When used in equations, wavelength is represented by the Greek letter lambda, λ. 2. Because wavelength is a distance measurement, it is expressed in the SI unit meters. XVII. The period measures how long it takes for waves to pass by. i. The time period required for one full wavelength of a wave to pass a certain point is called the Period of the wave. a. The period is also the time required for one complete vibration of a particle in a medium b. in equations; the period is represented by the symbol T. 1. Because the period is a time measurement, it is expressed in the SI unit seconds XVII. Frequency measures the rate of vibrations i. the frequency of a wave is the number of full wavelengths that pass a point in a given time interval a. the frequency of a wave also measures how rapidly vibrations occur in the medium, at the source of the wave, or both. ii. The symbol for frequency is f. a. the SI unit for measuring frequency is hertz (HZ), named after Heinrich Hertz who in 1888 became the first person to experimentally demonstrate electromagnetic waves. 1. Hertz units measure the number of vibrations per second iii. You can hear frequencies as low as 20 Hz, and as high as 20,000 Hz. a. when you hear 20,000 Hz, there are 20,000 compressions hitting your ear every second iv. Frequency Period equation frequency = 1/ period XVIII. Light comes in a wide range of frequencies and wavelengths i. our eyes can detect light with frequencies ranging from 4.3x 10^14 to 7.5x 10^14 a. light in this range is called visible light 1. The differences in frequency in visible light account for the different colors we see. ii. Electromagnetic waves also exist at other frequencies that we cannot see directly a. the full range of light at different frequencies and wavelengths is called the electromagnetic spectrum.