33อัตราเร็วคลื่น (Speed of wave) => ความเร็วเฟส คือความเร็วของหน้าคลื่นโดยพิจารณาความเร็วที่เฟสใดเฟสหนึ่งก็ได้ มีหน่วยเป็นเมตรต่อวินาทีจากนิยาม : v = Ds/Dtเมื่อคลื่นเคลื่อนที่ผ่านจุดๆ หนึ่งได้หนึ่งรอบ จะได้ระยะทาง = l และใช้เวลา = Tดังนั้น : v = l / Tแต่ : T = 1/fนั่นคือv = f • lSpeed = Wavelength • Frequency
34=> ความเร็วของอนุภาคตัวกลาง => ความเร็วกลุ่ม คือความเร็วของจุดศูนย์กลางกลุ่มคลื่นมักจะใช้กับคลื่นดลที่มีแอมปลิจูดไม่คงที่vg = Ds/Dt=> ความเร็วของอนุภาคตัวกลางเนื่องจากอนุภาคตัวกลางมีการสั่นหรือเคลื่อนที่เช่นเดียวกับวัตถุที่เคลื่อนแบบ SHMดังนั้น อัตราเร็วของอนุภาคตัวกลาง คือv = wA cos (wt)
36Check Your Understanding 1. The wavelength of the wave in the diagram above is given by letter ______.2. The amplitude of the wave in the diagram above is given by letter _____.
373. Indicate the interval which represents one full wavelength. a. A to Cb. B to Dc. A to Gd. C to G
384. As the frequency of a wave increases, the period of the wave ___________. a. decreasesb. increasesc. remains the same
395. A common physics lab involves the study of the oscillations of a pendulum. If apendulum makes 33 complete back-and-forth cycles of vibration in 11 seconds,then its period is ______.
406. A wave is introduced into a thin wire held tight at each end 6. A wave is introduced into a thin wire held tight at each end. It has an amplitude of 3.8 cm, a frequency of 51.2 Hz and a distance from a crest to the neighboring trough of 12.8 cm. Determine the period of such a wave.1/51.2 second5/256 second7. Frieda the fly flaps its wings back andforth 121 times each second. The periodof the wing flapping is ____ sec.1/121 second
418. A period of 5.0 seconds corresponds to a frequency of ________ Hertz.a b c d e9. Mac and Tosh stand 8 meters apart anddemonstrate the motion of a transversewave on a snakey. The wave e can bedescribed as having a vertical distance of32 cm from a trough to a crest, a frequencyof 2.4 Hz, and a horizontal distance of 48cmfrom a crest to the nearest trough.Determine the amplitude, period, andwavelength of such a wave.amplitude = 16 cm, Period = 5/12 s, wavelength = 96 cm
4210. A ruby-throated hummingbird beats its wings at a rate of about 70 wing beats persecond.a. What is the frequency in Hertz of the sound wave?b. Assuming the sound wave moves with a velocity of 350 m/s, what is the wavelength of the wave?F = 70 HzV = l f, l = 5 m
4311. Ocean waves are observed to travel along the water surface during a developingstorm. A coast weather station observesthat there is a guard vertical distance fromhigh point to low point of 4.6 meters and ahorizontal distance of 8.6 meters betweenadjacent crests. The waves splash into thestation once every 6.2 seconds. Determinethe frequency and the speed of thesewaves.
4412. Two boats are anchored 4 meters apart. They bob up and down, returning to thesame up position every 3 seconds. Whenone is up the other is down. There arenever any wave crests between theboats. Calculate the speed of the waves.
481. การอาศัยตัวกลางในการเคลื่อนที่ คลื่นกล mechanical waveA mechanical wave is a wave which is not capable of transmitting its energy through a vacuum. Mechanical waves require a medium in order to transport their energy from one location to another.คลื่นน้ำ เสียง คลื่นสปริงคลื่นในเส้นเชือก คลื่นสึนามิคลื่นแผ่นดินไหว ฯ
49คลื่นแม่เหล็กไฟฟ้า electromagnetic wave An electromagnetic wave is a wave which is capable of transmitting its energy through a vacuum.Electromagnetic waves are produced by the vibration of charged particles. Electromagnetic waves which are produced on the sun subsequently travel to Earth through the vacuum of outer space.เช่น คลื่นวิทยุ คลื่นไมโครเวฟ แสง รังสีเอกซ์ รังสี UV ฯ
815. A sound wave is different than a light wave in that a sound wave is produced by an oscillating object and alight wave is not.b. not capable of traveling through avacuum.c. not capable of diffracting and a lightwave is.d. capable of existing with a variety offrequencies and a light wave has asingle frequency.
826. A transverse wave is transporting energy from east to west 6. A transverse wave is transporting energy from east to west. The particles of the medium will move_____.a. east to west onlyb. both eastward and westwardc. north to south onlyd. both northward and southward
83Mechanical wave Electromagnetic wave Transverse wave longitudinal wave 7. A wave is transporting energy from left to right. The particles of the medium are moving back and forth in a leftward and rightward direction. This type of wave is known as a ____.Mechanical waveElectromagnetic waveTransverse wavelongitudinal wave
848. A sound wave is a mechanical wave; not an electromagnetic wave 8. A sound wave is a mechanical wave; not an electromagnetic wave. This means thata. particles of the medium move perpendicular to the direction of energy transport.b. a sound wave transports its energy through a vacuum.c. particles of the medium regularly and repeatedly oscillate about their rest position.d. a medium is required in order for sound waves to transport energy.
859. If you strike a horizontal rod vertically from above, what can be said about the waves created in the rod?a. The particles vibrate horizontally alongthe direction of the rod.b. The particles vibrate vertically,perpendicular to the direction of the rod.c. The particles vibrate in circles,d. The particles travel along the rod from the point of impact to its end.
8610. Which of the following is not a characteristic of mechanical waves? a. They consist of disturbances oroscillations of a medium.b. They transport energy.c. They travel in a direction which isat right angles to the direction ofthe particles of the medium.d. They are created by a vibratingsource.
8711. The sonar device on a fishing boat uses underwater sound to locatefish. Would you expect sonar to bea longitudinal or a transversewave?
891. TRUE or FALSE: In order for John to hear Jill, air molecules must move from the lips of Jill to the ears of John.FALSE
902. Curly and Moe are conducting a wave experiment using a slinky 2. Curly and Moe are conducting a wave experiment using a slinky. Curly introduces a disturbance into the slinky by giving it a quick back and forth jerk. Moe places his cheek (facial) at the opposite end of the slinky. Using the terminology of this unit, describe what Moe experiences as the pulse reaches the other end of the slinky.
913. Rhonda sends a pulse along a rope 3. Rhonda sends a pulse along a rope. How does the position of a point on the rope, before the pulse comes, compare to the position after the pulse has passed?
924. In order for a medium to be able to support a wave, the particles in the wave must be frictionless.isolated from one another.able to interact.very light.