Waves What Is a Wave Wave periodic disturbance
Waves
What Is a Wave? • Wave = periodic disturbance that transfers energy through space, matter, and time. • Energy may spread out as a wave travels. • When sound waves travel in air, the waves spread out in spheres. As they travel outward, the spherical wave fronts get bigger, so the energy in the waves spreads out over a larger area.
2 Main Types of Waves • Mechanical waves = require a medium. • Matter through which a wave travels is called the medium (air, water, earth, rope, metal, etc) • Electromagnetic waves (Light) = do not require a medium (can travel in a vacuum). • Light waves consist of changing electric and magnetic fields in space. • Travel at the speed of light (~300, 000 m/s in a vacuum)
Transverse and Longitudinal Waves • Longitudinal = wave in which the particles of the medium vibrate parallel to the direction of wave motion. • Sound waves and seismic P-waves are longitudinal. • Transverse = wave in which the particles of the medium move perpendicular to the direction the wave is traveling. • Light waves and seismic Swaves are transverse.
THINK! • What are the 2 ways waves carry energy? sketch each. • What is a ‘medium’ in your own words?
Parts of a Transverse Wave • An ideal transverse wave has the shape of a sine curve • Crest = highest point of a transverse wave. • Trough = lowest point of a transverse wave. • Amplitude = maximum distance that the particles of a wave’s medium vibrate from their rest position. • The energy of a mechanical wave is related to the amplitude. • Wavelength ( ) = distance from any point on a wave to an identical point on the next wave.
Understanding Waves • Frequency = number of complete waves (or cycles) per unit of time (usually seconds). Wavelength = 6 cm Frequency = 2 Hz 3 cm • The symbol for frequency is f. • The SI unit for measuring frequency is hertz (Hz). 1 second • Frequency – Wavelength Relationship • Shorter wavelength = higher frequency = more energy • Longer wavelength = lower frequency = less energy Wavelength = 12 cm Frequency = 1 Hz 3 cm 1 second
Wave Speed • Speed of a mechanical wave depends on the medium. • Mechanical waves generally travel: – fastest in solids – moderate in liquids – slowest in gases • All electromagnetic waves in empty space (a vacuum) travel at the speed of light, which is 300, 000 m/s (186, 000 mi/s). • EM waves travel slower in a medium
2. 5 cm Wavelength = _____ Amplitude = ______ 4 cm Frequency = _____ 4 Hz 4 cm 5 cm 8 cm Wavelength = _____ 10 cm Amplitude = ______ 8 cm Frequency = _____ 2 Hz 10 cm 20 cm Wavelength = _____ Amplitude = ______ 2 cm Frequency = _____ 1 Hz 2 cm 1 Second
THINK! • What is the relationship between wavelength and frequency?
Exit Ticket: Parts of a Wave 8 questions!! #1 - 8
1. Which letter indicates wavelength? A B C D AA B C A D
2. Which letter indicates trough? A B C D AA B C A D
3. Which letter indicates Amplitude? A B C D AA B C A D
4. Which letter indicates crest? A B C D AA B C A D
Chapter 14 5. Which of the following waves can be transmitted without a medium? A. electromagnetic B. longitudinal C. mechanical D. transverse
Chapter 14 6. How do longitudinal waves carry energy from a source? A. Particles vibrate outward from the source of the wave. B. Particles vibrate parallel to the direction of the wave. C. Particles vibrate perpendicular to the direction of the wave. D. Particles vibrate both parallel and perpendicular to the direction of the wave.
Chapter 14 7. What is measured by the amplitude of a wave? A. the amount of vibration of particles B. the direction of vibration of particles C. the rate of vibration of particles D. the wavelength of vibration of particles
8. In what medium do mechanical waves travel the fastest? A. Solids B. Gases C. Liquids D. Mechanical waves don’t travel in a medium.
Chapter 14 Parts of a Wave Exit Ticket - Short Answer Why do astronauts on the moon need a radio transmitter to carry on a conversation with each other?
Chapter 14 Understanding Concepts 5. Which of the following waves can be transmitted without a medium? A. electromagnetic B. longitudinal C. mechanical D. transverse
Chapter 14 Understanding Concepts 6. How do longitudinal waves carry energy from a source? A. Particles vibrate outward from the source of the wave. B. Particles vibrate parallel to the direction of the wave. C. Particles vibrate perpendicular to the direction of the wave. D. Particles vibrate both parallel and perpendicular to the direction of the wave.
Chapter 14 Understanding Concepts 7. What is measured by the amplitude of a wave? A. the amount of vibration of particles B. the direction of vibration of particles C. the rate of vibration of particles D. the wavelength of vibration of particles
Chapter 14 Understanding Concepts 4. Which combination of wave interactions can cause a standing wave? A. diffraction and interference B. diffraction and reflection C. reflection and interference D. reflection and refraction
Understanding Concepts 5. Why do astronauts on the moon need a radio transmitter to carry on a conversation with each other? Answer: Sound waves require a medium to carry energy from one place to another. On the moon, there is no air to carry the vibrations.
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