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Contemporary Physical Science
Quiz Date: 4/14/05
Chapter 17, Section 18.1 and Section 18.2
Study Guide
I. Key Terms and Points
Section 17.1
1. Mechanical Wave: a disturbance in matter that carries energy from one place to another.
2. Medium: materials through which a wave travels
3. Crest: the highest point of the wave above the rest position
4. Trough: the lowest point below the rest position
5. Transverse Wave: a wave that causes the medium to vibrate at right angles to the direction in which the wave travels
6. Compression: An are where the particles in a medium are spaced close together
7. Rarefaction: an area where the particles in a medium are spread out
8. Longitudinal Wave: a wave in which the vibration of the medium is parallel to the direction the wave travels
9. Surface Wave: a wave that travels along a surface separating two media
Key Points
Ø A mechanical wave is created when a source of energy causes a vibration to travel thorough a medium
Ø The three main types of mechanical waves are transverse waves, longitudinal waves, and surface waves.
Section 17.2
10. Periodic Motion: any motion that repeats at regular time intervals
11. Period: the time required for one cycle, a complete motion that returns to its starting point
12. Frequency: the number of complete cycles in a given time
13. Hertz: the unit in which frequency is measured
14. Wavelength: the distance between a point on one wave and the same point on the next cycle of the wave
15. Amplitude: the maximum displacement of the medium from a wave’s rest position
Key Points
Ø A wave’s frequency equals the frequency of the vibrating source producing the wave.
Ø Increasing the frequency of a wave decreases its wavelength.
Ø If waves are traveling at a constant speed, then wavelength is inversely proportional to frequency.
Ø The more energy a wave has, the greater is its amplitude.
Section 17.3
16. Reflection: this occurs when a wave bounces off a surface that it cannot pass through
17. Refraction: the bending of a wave as it enters a new medium at an angle
18. Diffraction: the bending of a wave as it moves around an obstacle or passes through a narrow opening
19. Interference: occurs when two or more waves overlap and combine together
20. Constructive Interference: occurs when two or more waves combine to produce a wave with a larger displacement
21. Destructive Interference: occurs when two or more waves combine to produce a wave with smaller displacements.
22. Standing Wave: a wave that appears to stay in one place-it does not seem to move through the medium
23. Node: a point on a standing wave that has no displacement from the rest position
Key Points:
Ø Reflection does not change the speed or frequency of a wave, but the wave can be flipped upside down.
Ø When a wave enters a medium at an angle, refraction occurs because one side of the wave moves more slowly than the other side.
Ø A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle
Ø Two types of interference are constructive interference and destructive interference.
Ø A standing wave forms only if half a wavelength or a multiple of half a wavelength fits exactly into the length of a vibrating cord.
Section 17.4
24. Sound Waves: longitudinal waves-compressions and rarefactions that travel through a medium
25. Loudness: a physical response to the intensity of sound, modified by physical factors.
26. Pitch: The frequencies of a sound as you perceive it.
27. Sonar: a technique for determining the distance to an object under water
28. Doppler Effect: a change in sound frequency caused by motion of the sound source, motion of the listener, or both.
29. Resonance: the response of a standing wave to another wave of the same frequency
Key Points
Ø Many behaviors of sound can be explained using a few properties-speed, intensity, loudness, and frequency and pitch.
Ø Ultrasound is used in a variety of applications, including sonar and ultrasound imaging.
Ø As a source of sound approaches, an observer hears a higher frequency. When the sound source moves away, the observer hears a lower frequency.
Ø The outer ear gathers and focuses sound into the middle ear, which receives and amplifies the vibrations. The inner ear uses nerve endings to sense vibrations and send signals to the brain.
Section 18.1
30. Electromagnetic Waves: Transverse waves consisting of changing electric fields and changing magnetic fields
31. Electromagnetic Radiation: the transfer of energy by electromagnetic waves traveling through matter or across space.
32. Intensity: the rate at which a wave’s energy flows through a given unit of area.
Key Points
Ø Electromagnetic waves are produced when an electric charge vibrates or accelerates
Ø Electromagnetic waves can travel through a vacuum, or empty space, as well as through matter
Ø The speed of light in a vacuum, c, is meters per second
Ø Electromagnetic waves vary in wavelength and frequency
Ø Electromagnetic radiation behaves sometimes like a wave and sometimes like a stream of particles.
Ø The intensity of light decreases as photons travel farther from the source.
Ø The electromagnetic spectrum includes radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays.
Section 18.2
33. Electromagnetic Spectrum: the full range of frequencies of electromagnetic radiation
Key Points:
Ø The electromagnetic spectrum includes radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays
Ø Radio waves are used in radio and television technologies, as well as in microwave ovens and radar.
Ø Infrared rays are used as a source of heat and to discover areas of heat differences.
Ø People use visible light to see, to help keep them save, and to communicate with one another.
Ø Ultraviolet rays have application in health and medicine, and in agriculture.
Ø X-Rays are used in medicine, industry, and transportation to make pictures of the inside of solid objects.
Ø Gamma rays are used in the medical field to kill cancer cells and make pictures of the brain and in industrial situations as an inspection tool.
II. Problems
Important Formulas
Speed of Sound =
Speed of Sound in Water =
Sample Problem #1
What is the Wavelength of 100.3 FM MHz?
Sample Problem #2
What is the wavelength of 880 AM KHz?
Sample Problem #3
Calculate the Depth of the water in the following problem.
Speed of Sound in Water=
Total Time = 3 Seconds
Diagram of a Transverse Wave
Sample Problem #4
Find the Wavelength Between points A and D
One Wavelength = 2 meters
A-B = .5 Wavelength
B-C = .5 Wavelength
C-D = .5 Wavelength
Wavelengths between A and D = 1.5 Wavelengths
3 meters
Sample Problem #5
Find the period of a wave if the frequency equals .1 Hz.
***Remember***
As frequency goes up wavelength goes down.
As wavelength goes up frequency goes down.
Sample Problem #6
Find the frequency of a wave with a period of 2 Seconds.
Practice Problems
1. Find the wavelength of 105.1 FM
2. Find the Wavelength of 101.1 FM
3. Find the wavelength of 97.1 FM
4. Find the Wavelength of 95.5 FM
5. Find the Wavelength of 770 AM
6. Find the Wavelength of 1010 AM
7. Find the Wavelength of 880 AM
8. Find the Wavelength of 1560AM
8. Calculate the depth of the water in the following problem.
9. Calculate the depth of the water in the following problem.
10. Calculate the Wavelength between points B and G
One Wavelength = 4 Meters
11. Calculate the Wavelength between points A and G
One Wavelength = 2 Meters
12. Calculate the Wavelength between points C and D.
One Wavelength = 2 Meters
13. Find the period of a Wave with the Frequency of .2 Hertz.
14. Find the period of a Wave with the Frequency of .5 Hertz.
15. Find the period of a Wave with the Frequency of .1 Hertz.
16. Find the Frequency of a Wave with the period of 20 Seconds.
17. Find the Frequency of a Wave with the period of 60 Seconds
18. Find the Frequency of a Wave with the period of 10 Seconds.