1. 14.2 Characteristics of Waves / 14.3 Wave Interactions I can: -recognize that waves may be absorbed by objects and be transformed into another energy. -explain that radiant energy travels in waves and does not require a medium. -recognize that sources of light energy radiate energy continually in all directions. -recognize that the EM spectrum has many different frequencies, wavelengths and energies. -determine everyday uses for the different bands of the EM spectrum. (e.g., infrared, visible light, etc.) -explain that radiant energy from the EM spectrum will travel at the same speed in a vacuum. -recognize which waves in the EM spectrum have the most energy in relationship to each other. (colors in visible light included)

2. The Parts of a Wave A transverse wave has alternating high points, called crests, and low points, called troughs.

3. The Parts of a Wave A compressional wave has no crests and troughs. Compression is a region where the coils are close together. The coils in the region next to a compression are spread apart, or less dense. rarefaction!

4. Wavelength wavelength: the distance between one point on a wave and the nearest point just like it. Transverse waves the wavelength is the distance from crest to crest or trough to trough.

5. Wavelength A wavelength in a compressional wave is the distance between two neighboring compressions or two neighboring rarefactions.

6. Frequency and Period The frequency of a wave is the number of wavelengths that pass a fixed point each second. Frequency= length/period expressed in hertz (Hz).

7. Frequency and Period The period of a wave is the amount of time it takes one wavelength to pass a point. frequency of a wave increases, the period decreases. units of seconds.

8. Wavelength is Related to Frequency As frequency increases, wavelength decreases. The frequency of a wave is always equal to the rate of vibration of the source that creates it. If you move the rope up, down, and back up in 1 s, the frequency of the wave you generate is 1 Hz.

9. Wavelength is Related to Frequency The speed of a wave depends on the medium it is traveling through. Sound waves usually travel faster in liquids and solids than they do in gases. Light waves travel more slowly in liquid and solids than they do in gases or in empty space. Sound waves usually travel faster in a material if the temperature of the material is increased.

10. Calculating Wave Speed You can calculate the speed of a wave represented by v by multiplying its frequency times its wavelength.

11. Amplitude and Energy Amplitude is related to the energy carried by a wave. Greater amplitude= more energy a wave carries. measured differently for compressional and transverse waves.

12. Amplitude of Compressional Waves The amplitude of a compressional wave is related to how tightly the medium is pushed together at the compressions. The denser the medium is at the compressions, the larger its amplitude is and the more energy the wave carries.

13. Amplitude of Compressional Waves The closer the coils are in a compression, the farther apart they are in a rarefaction. The less dense the medium is at the rarefactions, the more energy the wave carries.

14. Amplitude of Transverse Waves The amplitude of any transverse wave is the distance from the crest or trough of the wave to the rest position of the medium.

15. Doppler Effect

16. Wave Frequency of Light

17. Simulation  http://phet.colorado.edu/sims/wave-on-a- string/wave-on-a-string_en.html http://phet.colorado.edu/sims/wave-on-a- string/wave-on-a-string_en.html http://phet.colorado.edu/sims/wave-on-a- string/wave-on-a-string_en.html

18. Question 1 If a wave has a high point and a low point, is it a compressional or transverse wave?

19. Answer Transverse waves have alternating high points, called crests, and low points, called troughs.

20. Question 2 What is the wavelength of a wave?

21. Answer A wavelength is the distance between one point on a wave and the nearest point just like it.

22. Question 3 Which of the following refers to the number of wavelengths that pass a fixed point each second?   A. frequency   B. period   C. wavelength   D. wave speed

23. Answer The answer is A. Period is a length of time, and wavelength is a distance.

24. 14.3- Wave Interactions I can: -explain and give examples of diffraction, reflection and refraction. -describe what happens when two waves can pass through one another and then continue traveling in the same direction as before. -predict that when waves meet they can undergo constructive or destructive interference. -explain that sound undergoes reflection, refraction, interference and diffraction. -identify that radiant energy exhibits reflection, refraction, absorption, superposition and diffraction depending on the medium. -explain that opaque objects will transmit little radiant energy, but they can absorb or reflect radiant energy. -differentiate between diffuse (rough) or regular (smooth) reflection. -explain that transparent materials transmit most of the energy through it but can absorb or reflect smaller amounts.

25. Reflection Reflection occurs when a wave strikes an object and bounces off of it. All types of waves—including sound, water, and light waves—can be reflected.

26. Reflection How does the reflection of light allow you to see yourself in the mirror? It happens in two steps. First, light strikes your face and bounces off. Then, the light reflected off your face strikes the mirror and is reflected into your eyes.

27. Echoes A similar thing happens to sound waves when your footsteps echo. Sound waves form and the waves travel through the air to both your ears and other objects. Sometimes the sound waves hit another object, they reflect off it and come back to you. Your ears hear the sound again, a few seconds after you first heard your footstep.

28. The Law of Reflection The beam striking the mirror is called the incident beam. The beam that bounces off the mirror is called the reflected beam. The line drawn perpendicular to the surface of the mirror is called the normal.

29. The Law of Reflection The angle formed by the incident beam and the normal is the angle of incidence. The angle formed by the reflected beam and the normal is the angle of reflection.

30. The Law of Reflection According to the law of reflection, the angle of incidence is equal to the angle of reflection. All reflected waves obey this law.

31. Refraction When a wave passes from one medium to another—such as when a light wave passes from air to water—it changes speed. Bend may occur

32. Refraction Refraction is the bending of a wave caused by a change in its speed as it moves from one medium to another.

33. Refraction of Light in Water Light waves travel slower in water than in air. When light waves travel from air to water, they slow down and bend toward the normal.

34. Refraction of Light in Water When light waves travel from water to air, they speed up and bend away from the normal.

35. Refraction of Light in Water You may have noticed that objects that are underwater seem closer to the surface than they really are. In the figure, the light waves reflected from the swimmer’s foot are refracted away from the normal and enter your eyes. Your brain assumes that all light waves have traveled in a straight line. The light waves that enter your eyes seem to have come from a foot that was higher in the water.

36. Review When waves strike an object, several things can happen… The waves can bounce off, or be reflected. If the object is transparent, light waves can be refracted as they pass through it. Waves also can behave another way when they strike an object. The waves can bend around the object.

37. Diffraction Diffraction occurs when an object causes a wave to change direction and bend around it. Diffraction and refraction both cause waves to bend. The difference is that refraction occurs when waves pass through an object, while diffraction occurs when waves pass around an object.

38. Diffraction Waves also can be diffracted when they pass through a narrow opening. After they pass through the opening, the waves spread out.

39. Diffraction and Wavelength The amount of diffraction that occurs depends on how big the obstacle or opening is compared to the wavelength. When obstacle is smaller than the wavelength, the waves bend around it. If the obstacle is larger than the wavelength, the waves do not diffract as much. In fact, if the obstacle is much larger than the wavelength, almost no diffraction occurs.

40. Examples You’re walking down the hallway and you can hear sounds coming from the lunchroom before you reach the open lunchroom door. The wavelengths of sound waves are similar in size to a door opening. Sound waves diffract around the door and spread out down the hallway. Light waves have a much shorter wavelength. They are hardly diffracted at all by the door.

41. Interference When two or more waves overlap and combine to form a new wave, the process is called interference.

42. Constructive Interference In constructive interference, the waves add together. Crests of two or more transverse waves arrive at the same place at the same time and overlap.

43. Constructive Interference The amplitude of the new wave that forms is equal to the sum of the amplitudes of the original waves.

44. Destructive Interference The waves subtract from each other as they overlap. Crests of one transverse wave meets the troughs of another transverse wave.

45. Destructive Interference The amplitude of the new wave is the difference between the amplitudes of the waves that overlapped. Waves undergoing destructive interference are said to be out of phase.

46. Standing Waves A standing wave waves equal in wavelength and amplitude, but traveling in opposite directions, continuously interfere with each other. Appear to be standing still.

47. Resonance The process by which an object is made to vibrate by absorbing energy at its natural frequencies is call resonance. If enough energy is absorbed, the object can vibrate so strongly that it breaks apart.

48. Question 1 State the law of reflection. Answer According to the law of reflection, the angle of incidence is equal to the angle of reflection.

49. Question 2 __________ is the bending of a wave caused by a change in its speed as it moves from one medium to another.   A. Diffraction   B. Diffusion   C. Refraction   D. Reflection

50. Answer The answer is C. The greater the change in speed is, the more the wave bends.

51. Question 3 Which is the means by which you can hear around corners?   A. diffraction   B. diffusion   C. reflection   D. refraction

52. Answer The answer is A. Diffraction occurs when an object causes a wave to change direction and bend around it.