org are unblocked. Waves and Sound Practice Quiz Multiple Choice Identify the choice that best completes the statement or answers the question. Fourteen years of research by Bose Corporation bring you the benefits of award-winning patented acoustic waveguide speaker technology. ongil udit na l c. Answer the following questions during or after your study of Wave Properties. It demonstrates waves in two dimensions, including such wave phenomena as interference, diffraction (single slit, double slit, etc. 5The diagram below shows an oscilloscope with a sound wave produced by a musical. Sound is a compression wave caused by vibrations. _____ waves have a color spectrum known as ROYGBIV. Understand the sound is a form of energy. Sound waves move through air into your ears. It's a simple, easy and pretty awesome experiment that explores the science of sound waves and how they travel. •Amechanical wave is a disturbance in matter that carries energy from one place to another. Some examples of waves include; water waves, sound waves, and radio waves. Test Your Knowledge - and learn some interesting things along the way. For a light wave, it corresponds to the colour of light. Chapter 10--Wave Motion 343 would look like if our eyes were sensitive to very subtle pressure variations--Figure 10. This is often a good solution since it utilizes unused volume for a product. What Is Sound? Sound is a pressure wave which is created by a vibrating object. The book explains the basic concepts of waves and oscillations through the method of solving problems and it is designed to be used as a textbook for a formal course on the subject. The downhole receiver(s) may be positioned at selected test depths in a borehole or. Frequency - the number of waves produced in a given time Frequency= waves/time Wave Velocity - is the speed with which a wave crest passes by a particular point in space It is measured in meters/second. Measurement done at 1/3 and 2/3 height of tank A weighted sound pressure level is computed. Does light interact with a detector in a wavelike way or in a particle-like way? Depends how you look at it, but most often as a particle since its energy is delivered in chunks or quanta. none of the above 2. Convex surfaces do just the opposite; they tend to disperse sound in multiple directions. Some of the sound waves are reflected and inverted, while the rest are transmitted through the steel barrier. Two waves (with 2 cm and 3 cm amplitudes, respectively) can interfere and create a resultant wave with 6 cm amplitude. AZ1639 Revised 10/15 Sonic PeSt RePellentS Nicholas Aflitto and Tom DeGomez Introduction Sonic pest devices are tools that emit sound in the attempt to repel, deter, or kill unwanted animals such as insects, rodents,. What is the speed of sound on this day at her location? 2. Reference Materials and Tools Each student taking the high school Introductory Physics test was provided with an Introductory Physics Formula Sheet. The length, height, and speed of a sound wave determine how a listener perceives the sound. Explain how the sound travels. longitudinal wave and transverse wave. Both the wavelength of the water waves and the velocity of the water waves will remain the same. Ocean waves are mechanical waves, sound waves are. Waves Foldable PowerPoint KEY. • Sound cannot travel through a vacuum—sound must travel through a medium. This unit explains what sound is, how it travels, and some of the properties of sound, such as pitch and volume. Sound is a kind of energy. These vibrations are passed along to nearby particles, which then pass them on again. Which of the following types of waves requires a medium: microwave, visible light, sound waves or x-rays? Sound waves. The main content is an entirely new presentation. Chapter 17: Waves II Example: Two point sources separated by 16m emit coherent sound waves with =2m. trough period crest node. The note middle C, for example, creates 256 vibrations, or compressions, every second. Explore the wonderful world of waves! Even observe a string vibrate in slow motion. Downhole receivers are used to detect the arrival of the seismic wave train. They're permanent waves 2. Sound waves bounce just like water waves and rope waves. sound waves). The critical angle and optical fibres. Sound can also mean a body of water, like a bay or channel. Extn: Use a water tray to show ripple wave effect. Unit Test – SPH3U Grade 11 Physics – Waves and Sound Length of pipe = ¼ * wavelength (8 marks) 2. Sound Quiz 1. A medium is necessary for the propagation of sound waves. λ = 330 ÷ 500 = 0·66 m. Your radon levels are accessible through the Airthings App and the Airthings Dashboard. Waves, Light and Sound Unit Test Accelerated Science 8 – Version A Page 1 Waves, Light and Sound Unit Test Accelerated Science 8 – Version A Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. They're electromagnetic waves c. School Physics Quiz : Sound Waves Answer the following questions based on sound waves. Sound, like light, travels in waves as can be seen in the diagram below. Are sound waves transverse waves or longitudinal waves? Why? Longitudinal waves because. Instructions: Please answer the questions below about your sleep habits over the past 4 weeks. This solution is a wave \traveling" in the direction of k in the sense that a point of constant phase, meaning k¢x¡!t= constant, moves along this direction with a speed vwhich is !=k. [Clarification Statement: Emphasis is on a basic understanding that waves can be used for communication purposes. Because alternating current is a wave phenomenon, it shares many of the properties of other wave phenomena, like sound. The frequency of sound is the number of wavelengths in a given unit of time. The wavelength of sound is the distance between two compressions or between two rarefactions. PHYSICS TEST PRACTICE BOOK This practice book contains one actual full-length GRE Physics Test test-taking strategies Become familiar with test structure and content test instructions and answering procedures Compare your practice test results with the performance of those who took. Sound waves require matter to travel while light does not. For two wave sources vibrating in phase, a difference in path lengths that is zero or an integer number (1, 2, 3,. Structure of ear The worksheets are useful for KS3 students, especially Year 8 students to revise and master the topic. Waves: Introduction and Types A wave is a transfer of energy through a medium from one point to another. Use your understanding of the transmission of sound and the table to answer the following question. The first of these is Yashiro Shrine, which is near the crest of the island and. If a wave's speed is 25 m/s, and its wavelength is 5. Move the listener around and hear what she hears. A transverse wave consists of oscillations perpendicular to the direction of propagation. Sound waves: A wave is an oscillating disturbance that travels through a medium. GUIDELINES ON THE ACOUSTICS OF SOUND FIELD AUDIOMETRY IN CLINICAL AUDIOLOGICAL APPLICATIONS 1. 69kb; Physics 07-05 Doppler Effect and Sonic. Unit 4 : Waves, Sound, and Light Use these animations, simulations, tutorials, and links to help you learn more about Waves, Sound, and Light. The sensitivity of these maneuvers is limited by the amount of peritoneal fluid present, and ultrasound is useful in defining small amounts of fluid. Soundwaves is a Surf, Skate, Music store located in Houston, Texas. Visible light passing through a window. waves will increase. Mathematics, Science and Language Objectives Mathematics The student will 1. Make sure to remember your password. The City School /Reinforcement Worksheet/EoY 2016-17/Science/Class 8/Sound and HearingPage 3 of 4 Q. Start here Surface Conditions Report. These examples are from the Cambridge English Corpus and from sources on the web. 13 Waves & Sound 13a1_waves_and_sound. • If you need long range and have limited space, then talk to an antenna expert !. Matter and Energy Waves, Sound, and Light :. Teacher gives a brief lesson on transverse and compression waves a. Properties of Sound Pitch - description of how high or low the sound seems to a person. Joe Wolfe1, School of Physics, The University of New South Wales, Sydney. Pitch is determined by the vibration rate of the sound source. Largest US underground test was ~ 5MT Increasing the pressure amplitude of a sound wave by a factor of 4 (while. Functionality. • Sound cannot travel through a vacuum—sound must travel through a medium. What is the order of increasing density of the materials that you are testing? In this lab you can hear differences in sound when the sound waves travel through various materials. ) prior to acoustic evaluation sional wave that typically has a significantly smaller (Fig. It is used to help diagnose pain or distention (enlargement) and evaluate the kidneys, liver, gallbladder, bile ducts, pancreas, spleen and abdominal aorta. particles in the medium oscillate perpendicular to the direction the wave travels b. Draw a transverse and a longitudinal wave. It’s also known as sonography. True or False. P-waves are sound waves, it's just that in seismology we are interested in frequencies that are lower than humans' range of hearing (the speed of sound in air is about 0. The inner ear contains the auditory (hearing) nerve, which leads to the brain. 5 wavelengths 4. Light, Sound, and Waves Test Study Guide Directions: Answer the following questions to help you study for your test. ©Modeling Instruction Program 2004 1 W2, Mechanical Waves in 1D, WS 5 v3. The first of these is Yashiro Shrine, which is near the crest of the island and. 6th - 7th grade. Assess students knowledge of sound waves by using the multiple choice quiz. That is why the further away a sound is, the softer it seems. Explain that we use different ways to measure how loud a sound is or the distance a sound can travel and still be heard. The height of the wave (amplitude) and the closeness of the waves to each other (frequency) is how we measure volume and pitch. They're permanent waves 2. 5 Transverse Waves (pages 497) 26. Water waves are an example of transverse waves. Reference Materials and Tools Each student taking the high school Introductory Physics test was provided with an Introductory Physics Formula Sheet. Sound waves are longitudinal waves originating from a source and conveyed through a medium (gaseous, liquid or solid). Yet, how many people can be lazy. 1 Type of sound field 3. Microphone at the other with output going in sound card for further processing. Show all work, and use the factor-label method to perform all necessary conversions. C) There is a rainbow present in the sky. Electromagnetic spectrum Infrared waves Radio waves Wavelength Frequency Microwaves Ultraviolet rays X rays Use your notes from pages 9 – 10 and the terms in the vocabulary box to fill in the blanks for the following nine questions. EM Wave • EM waves are generated by vibrating electrons • Composed of two perpendicular oscillating fields • Can be characterized by its frequency, which is inversely related to wavelength (f = c / λ) • Shares with sound the properties of spreading loss, attenuation,. A wave is a way of transporting energy long distances without actually transporting matter. A sound wave has a frequency of 3250 Hz and a wavelength of 0·1 m. A wave, whether it is in the ocean, on land, or in the air, is simply the movement that takes energy from one place to another. As a sound wave travels through air there is a net transfer of ____. TWICE THE FREQUENCY MEANS HALF THE WAVELENGTH, SO SOURCE A HAS HALF THE WAVELENGTH. Partial credit is available if your work is clear. Its wavelength gets longer. The _____ is found at the top of a wave. 6th - 7th grade. While it does. The interval representing one wavelength is 28. The level of difficulty is similar to the Pure. Resonance and the Speed of Sound 1. During a thunderstorm, the fact that you can see the lightning before you hear the thunderclap tells you what? a. Digital audio editing software with advanced audio restoration effects and processing tools. ' visible light. Wave Worksheet. Sound and earthquake waves are examples. Ferry and Satellite. The energy to which the human ears are sensitive is known as sound. The drum surface vibrates back. A FREE A-level physics resource,secondary,college,high school revision, providing physics worksheets,. WARNING: For most waves thought about in physics, like sound waves or light waves, when you change the frequency, you also change the wavelength. wave will follow the bullet and will be transmitted from the muzzle back to the microphone position. Downhole receivers are used to detect the arrival of the seismic wave train. Medium Energy Matter or Space Mechanical Vibrating Molecules Waves Repeating Disturbance Compressional Transverse Neighbor Molecules are or are produced by which pass energy to that need a that transfers are called and can be either through. Sound waves can bounce off smooth, hard objects in the same way as a rubber ball bounces off the ground. They are frequency, speed, and amplitude. Ultrasound Quiz 1 ~ First name ~ ~ Last name ~ The active element of most acoustic transducers used today is: Lithium Piezoelectric ceramic Sulfide Quartz The measure of how a signal from a defect compared to other background reflections is called: Acoustic impedance Signal to noise ratio Refraction Reflection. Ocean waves are transverse waves, sound waves are longitudinal waves. 1 Notation Sound is a longitudinal wave, in both position and pressure/density, as we’ll see. ocean waves c. Determine the period of such a wave. 5) Which of the following statements is CORRECT regarding the standing wave diagram below? A) This is a diagram of the fourth overtone. 4 October 16, 2001 AM253543_03_V. Sort the following according to how fast sound will travel through the medium: liquid, solid, gas. _____ waves have a color spectrum known as ROYGBIV. The distance from one crest of a wave to the crest of the next wave is the: A wavelength B frequency C amplitude: 5. supernode e. Partial credit is available if your work is clear. This Science quiz is called 'Physics - The Study of Sound' and it has been written by teachers to help you if you are studying the subject at middle school. none of the above 2. For example, when a loud sound is heard, it is because many molecules have been vibrated with much force. Which of the following is not a property of acoustic waves? Pressure and particle velocity are in-phase. The app communicates with your Wave via Bluetooth Low Energy, giving the Wave a battery lifetime of up to two years. Interference of Sound Waves"--Sound waves may interfere with each other,! producing either constructive or destructive! interference. Sound Power and Pressure Measurements What is a decibel? The decibel (dB) is a logarithmic unit used to describe a ratio. Submarines, ships, and marine mammals all make noise or produce sound waves. Wave A wave is a vibratory disturbance in a medium which carries energy from one point to another point without any actual movement of the medium. Edexcel GCSE (9-1) Physics SP4 Waves Test With Mark Scheme 16_17 - Free download as PDF File (. Resonance and the Speed of Sound 1. Over the past few weeks, we have discovered the different patterns associated with sound and how to measure how high or low it is. Waves, Light and Sound Unit Test Accelerated Science 8 – Version A Page 1 Waves, Light and Sound Unit Test Accelerated Science 8 – Version A Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. The movement of a wave is complicated, but both electromagnetic and physical waves use similar ways to describe the motion. Echoes can be heard in small spaces with hard walls, like wells, or. Sound Waves Review for Test. This test covers the topics of Waves, Light, Sound and Electromagnetic Spectrum. Some examples of waves include; water waves, sound waves, and radio waves. transverse b. What part of the wave determines the loudness of a sound or the brightness of a light? a. These lessons focus on students collaboratively problem solving, discovering and investigating to find answers and solutions. The high school Introductory Physics test included two separate test sessions, which were administered on consecutive days. Over the past few weeks, we have discovered the different patterns associated with sound and how to measure how high or low it is. This is a quiz designed for grade 8-10 physical science students, testing their knowledge of basic wave properties which includes concepts of refraction, reflection, wave types, and basic formulas. This StudyJams! activity will teach students more about how sound waves work. What Is Sound? Sound is a pressure wave which is created by a vibrating object. Students will learn about different topics such as; The Nature and Propagation of Sound Waves; Displacement Wave and Pressure Wave; Speed of a Sound Wave in a Material Medium; Speed of Sound in a Gas: Newton’s Formula and Laplace’s Correction. It is encouraged that students take notes and teacher uses strategies to help. 1 Ultrasonic Definition The human ear can hear sound frequenc y around 20HZ ~ 20KHZ, and ultraso nic is the sound wave beyond the human ability of 20KHZ. This is often a good solution since it utilizes unused volume for a product. Instructions: To take the quiz, click on the answer. All rights reserved. You'll get new matches each time. From a more practical point of view, this term describes the. These and other waves move at different speeds in different materials. Kahoot Waves Review Quiz 1. Ocean waves are longitudinal waves, sound waves are transverse waves. From waves and lasers to lenses and colors, the Light Science series explores the basic science concepts involved in seeing, using, and understanding this form of energy. Sound waves are variations in air pressures above and below the ambient pressure. Reference Materials and Tools Each student taking the high school Introductory Physics test was provided with an Introductory Physics Formula Sheet. 0 m, then its period must be 0. Waves Unit Test 1 Study Guide | Waves Unit Test 1 Study Guide KEY Click on the links below for resources by Essential Question: EQ 1: What are the characteristics of mechanical and electromagnetic waves? EQ 2: How do changes in one part of a wave affect other parts of a wave? EQ 3: How are sound waves affected by changes in amplitude and pitch?. To understand how to determine the interference conditions for double slit interference 3. During complete destructive interference, which of the following could be produced? a. Wave Worksheet. The following gives you an idea of the features of the Praat program. The waves are generated with the same amplitude and phase. The first choice for Grammy-winning mixing engineers, music producers, musicians and sound designers, Waves is the world-leading maker of audio plugins, software and hardware for audio mixing, music production, mastering, post-production and live sound. Many forms of energy, including sound, travel in the form of waves. For example, when a loud sound is heard, it is because many molecules have been vibrated with much force. The Physics Hypertextbook is a reaction to the three big problems with textbooks: lack of writer's voice, layouts that reduce readability, and outdated economics. Selina Concise Physics Class 9 ICSE Solutions Propagation of Sound Waves ICSE SolutionsSelina ICSE Solutions APlusTopper. There is a Powerpoint and a paper version to use in class or for homework. 0 m, then its period must be 0. ) That sound travels faster than light. ongil udit na l c. Frequency and Amplitude of Sound KEY. Get an answer for 'How are sound and light alike and different?' and find homework help for other Science questions at eNotes. Student Worksheet. About This Quiz & Worksheet. It's moving through a denser medium. 13-03-073. A sound wave consists of a series of. Sound Forums Network, LLC was co-founded by David Karol and Bennett Prescott to provide and preserve a home for audio professionals around the world. of wave propagation for longitudinal waves and shear waves. 2b graphs pressure variation versus position for sound at a given point in time). To understand how to determine the intensity of the light associated with double slit interference. The wave on a vibrating violin string is an example of a transverse wave. 95MB WAVES AND SOUND MULTIPLE CHOICE TEST As Pdf, AND WAVES MULTIPLE SOUND TEST CHOICE As Docx, CHOICE MULTIPLE SOUND AND WAVES TEST As Pptx WAVES AND SOUND MULTIPLE CHOICE TEST How easy reading concept can improve to be an effective person? WAVES AND SOUND MULTIPLE CHOICE TEST review is a very simple task. Understand the sound is a form of energy. Some of these waves are compressional, and others are transverse. It is of particular interest to pass square waves through the differentiating and integrating networks shown in (b) and (c). It forms a major means of communication in the form of spoken language and both natural and manmade sounds contribute greatly to our environment. none of the above 2. The waves are generated with the same amplitude and phase. If a resonance condition is met, the open end of the. Sound cannot travel in vaccum because there is no material medium in vaccum. Students will learn about different topics such as; The Nature and Propagation of Sound Waves; Displacement Wave and Pressure Wave; Speed of a Sound Wave in a Material Medium; Speed of Sound in a Gas: Newton’s Formula and Laplace’s Correction. Review Game 8. For example, imagine a drum being hit with a mallet. Rubber absorbs or reduces vibrations, so sound waves do not travel through it well. Waves Unit Test 1 Study Guide | Waves Unit Test 1 Study Guide KEY Click on the links below for resources by Essential Question: EQ 1: What are the characteristics of mechanical and electromagnetic waves? EQ 2: How do changes in one part of a wave affect other parts of a wave? EQ 3: How are sound waves affected by changes in amplitude and pitch?. Do I understand sound? Multiple choice sound waves quiz. If the frequency of the source is 2. pdf topic notes,You-Tube videos,specimen physics exam papers and social media for extra physics help. The circle next to the answer will turn yellow. crest-and-trough d. trough period crest node. A sound velocity table is a list of the speed of sound in various materials. If a sound wave is observed to travel a distance of 700 meters in 2 seconds, then the speed of the wave would be 350 m/s. Thus, this term represents the sound generation due purely to the dynamics of the vortex centroids. Hypersound, sometimes called praetersound or microsound, is sound waves of frequencies greater than 10 13 hertz. Anatomy of a Wave KEY. The above animation is not meant to show what happens specifically with sound and light waves. It also shows you how to calculate sound. (vi)What does this indicate about the difference between sound waves and light waves? (vii) State one other difference between sound waves and light waves. Physics 1120: Standing Waves and Sound Level Solutions Sound Level 1. $ The medium's position is about the same as its original position. Instructions: Please answer the questions below about your sleep habits over the past 4 weeks. When particles in the medium vibrate parallel to. Adobe Animate offers several ways to use sound. period frequency wavelength amplitude 3. April 8, 2013. CBSE Class 9 Physics Worksheet - Sound - Practice worksheets for CBSE students. Sound Quiz (6. Explosions in space can be heard therefore sound does travel in space Unit Test - SPH3U Grade 11 Physics - Waves and Sound. Two waves (with 2 cm and 3 cm amplitudes, respectively) can interfere and create a resultant wave with 6 cm amplitude. The links take you into the web copy of the manual. Students will learn about different topics such as; The Nature and Propagation of Sound Waves; Displacement Wave and Pressure Wave; Speed of a Sound Wave in a Material Medium; Speed of Sound in a Gas: Newton’s Formula and Laplace’s Correction. Light and sound waves interact with different mediums in different ways. Sound waves generated within a room either pass through the room boundaries, bounce off them, or are absorbed. _____ is the number of waves that occur in 1 second. Waves are a means of transporting energy from one location to another without actually displacing matter from one location to another. Sound is created by vibration and cannot travel through a vacuum. Electromagnetic Pulse: Effects on the U. Explain the sound wave in terms of amplitude and wavelength. Sound waves in air travel at approximately 330m/s. They also have an SMSC opp. It also shows you how to calculate sound. The region of a sound wave in which air molecules are pushed closer together is called a(n) _____. Figure A illustrates the difference between longitudinal and transverse waves. Ultrasonic Inspection (UT) Attenuation • The loss in acoustic energy which occurs between any two points of travel • Primarily due to scattering and absorption – Scatter – dispersion of ultrasonic waves – Absorption – conversion of sound waves into another energy form (heat) • Higher frequency produce more scatter so penetrating power. The circle next to the answer will turn yellow. Waves in which the medium moves at right angles (perpendicular) to the direction of the wave (looks like a jump rope). 2 cm) You can “curl up” such an antenna and make a helical antenna. Sideways vibration of stretched string. This simulation lets you see sound waves. While it does. A wave is some disturbance caused when energy is traveling from one object to another. Class Instrumentation Ltd Ultrasonic Sound Velocity Table. What do seismic waves and sound waves have in common? a. You can select the combination of books and teaching resources to suit either your own classroom, or your whole school. Animals like dogs have a higher frequency of hearing sounds. Contents EARTH SCIENCE CHAPTER 4 Earth’s Water Chapter Concept Map. Did You Know? Synonym Discussion of sound. They have wavelengths between 1 centimetre and 10 metres, and will easily diffract round corners. dB table sound pressure levels SPL level test normal voice sound levels sound units decibel level common sounds sound intensity decibel comparison chart noise ratio Conversion of sound pressure to sound intensity calculation compression rarefaction loudness decibel dB scale ratio factor units - Eberhard Sengpiel sengpielaudio. Conner, MA Biological Sciences Home Class information STEAM TOPICS > > > > > > Science BLOG HOMEWORK SECTION > > "Sound" Practice Quiz. • A quarter wave antenna is an easy and good solution, but it is not small (433 MHz: 16. sinusoidal wave is traveling on the cord, the speed of each piece of the cord will be given by the speed relationship of a simple harmonic oscillator (Equation 11-9), which depends on the amplitude of the wave, the frequency of the wave, and the specific time of observation. Within these stations, students learn about sound waves, construct a phone, diagram different types of waves, model vibrations, learn about ocean waves, and learn about transverse and longitudinal waves. In this Mystery, students discover that sound is a wave. Partial credit is available if your work is clear. The time between the P- and S-waves is routinely used to determine the distance to their source, the epicenter of the earthquake. Contents EARTH SCIENCE CHAPTER 4 Earth’s Water Chapter Concept Map. Figure A illustrates the difference between longitudinal and transverse waves. com, Elsevier’s leading platform of peer-reviewed scholarly literature. It has an amplitude of 3. Class Instrumentation Ltd Ultrasonic Sound Velocity Table. In other words, the amplitude of the standing waves must be zero at the water's surface. Sinusoidal wave going trough entire human audio spectrum, starting at 20Hz and ending at 20kHz. Physics Revision Notes – Waves 1. Which of the following best represents the sound wave if the source is moving away from the observer?. Read the questions carefully and answer. As great as Newton was, his particle theory of light has failed. Sound waves: A wave is an oscillating disturbance that travels through a medium. Definition 2. The higher the frequency, the more energy in the wave. refracted sound wave. • Sound cannot travel through a vacuum—sound must travel through a medium. This physics video tutorial explains the concept of sound waves and how shows you how to calculate the wavelength, frequency, and velocity of sound waves. Based on your answer to question 26, explain why sound travels fastest through the particular medium. Which wave has the highest frequency? Wave 2 5. Which wave belongs to the baby's voice?____Wave 2_____ A D B E C 1. · Test your idea with a variety of waves. Calculate the speed of sound. 0 atm and 20 o C is 343 m/s. Assessment / Evaluation of Students The instructor may assess the students in any/all of the following manners: 1. Grove - Sound Sensor. At the end of the chapter, Quiz Can sound waves be heard in outer space? Why? No, as sound wave requires a medium to travel. frequency b. In air, molecules push and (efiectively, relative to equilibrium) pull on each other, so. Scroll down to section 4, "Collision of Waves": When two waves traveling in opposite directions through the same medium collide, the amplitude of the resulting wave will be the sum of the two initial waves, this is called _____.