Waves WAVE periodic disturbance that transfers energy through

Waves

• 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: 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)

2 Ways Waves are Shaped/Transport Energy • LONGITUDINAL WAVE: 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 WAVES: wave in which the particles of the medium move perpendicular to the direction the wave is traveling. • Light waves and seismic S-waves 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 (λ) = distance from any point on a wave to an identical point on the next wave.

• 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

MECHANICAL WAVE SPEED • Speed of a mechanical wave depends on the medium. • Mechanical waves generally travel: – fastest in solids – moderate in liquids – slowest in gases ELECTROMAGNETIC WAVE SPEED • 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 = _____ 4 cm Amplitude = _____ 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 #1 -4

1. Which letter indicates wavelength? A B AA C C D B A D

2. Which letter indicates trough? A B AA C C D B A D

3. Which letter indicates Amplitude? A B AA C C D B A D

4. Which letter indicates crest? A B AA C C D B A D

Properties of Waves Four Defining Properties of Waves plus Polarization and Doppler Effect

• #1 REFLECTION: The bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through (echo, mirror image, etc. ). • #2 DIFFRACTION: The bending of waves around an edge.

• # 3 REFRACTION: Bending of waves when passing from one medium to another at an angle • Caused by a change in speed of the wave • White light disperses into the separate colors (ROYGBIV) in a prism or raindrop

• Waves in the same place combine to produce a single wave… • #4 INTERFERENCE: Combination of two or more waves of the same frequency that results in a single wave. • Resulting wave can be found by adding the amplitude of the waves at each point. • Crests are considered positive, and troughs are considered negative. • Principle of SUPERPOSITION: When 2 waves interfere, the resulting wave is a combination of the first 2 waves

• CONSTRUCTIVE INTERFERENCE: waves combine so that the resulting wave is bigger than the original waves; the amplitude increases. • DESTRUCTIVE INTERFERENCE: waves combine so that the resulting wave is smaller than the largest of the original waves; the amplitude decreases. • Waves cancel each other out (sound canceling headphones)

Applications of Wave Properties • Color on Soap Bubbles • Result of interference and double reflection • Rainbows • Refraction – Reflection – Refraction • Fiber optics • Use total internal reflection • TIR = complete reflection that takes place within a substance when the angle of incidence of light striking the surface boundary is less than the critical angle.

Blue Sky & Red Sunsets • Molecules in atmosphere scatter light rays. • Shorter wavelengths (blue, violet) are scattered more easily. SUNSET • more atmosphere • more scattering • orange-red sky & sun NOON • less atmosphere • less scattering • blue sky, yellow sun

• Polarization (Property of Light Waves) • Causing light waves to be oriented in a single plane

• The pitch of a sound (how high or low) is determined by the frequency at which sound waves strike the eardrum in your ear. • Higher-pitched sound is caused by sound waves of higher frequency and vice-versa. • Frequency changes when the source of waves is moving. • Doppler effect = observed change in the frequency of a wave when the source or observer is moving. • Shorter wavelengths/high frequency in front of the moving source • Longer wavelengths/low frequency behind the moving source

Chapter 14 Understanding Concepts 1. Which of the following waves can be transmitted without a medium? A. electromagnetic B. longitudinal C. mechanical D. transverse

Chapter 14 Understanding Concepts 2. How do longitudinal waves carry energy from a source? F. Particles vibrate outward from the source of the wave. G. Particles vibrate parallel to the direction of the wave. H. Particles vibrate perpendicular to the direction of the wave. I. Particles vibrate both parallel and perpendicular to the direction of the wave.

Chapter 14 Understanding Concepts 3. 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? F. diffraction and interference G. diffraction and reflection H. reflection and interference I. reflection and refraction

Chapter 14 Understanding Concepts 5. Why do astronauts on the moon need a radio transmitter to carry on a conversation with each other?

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.

Reading Skills The Doppler Effect applies to light as well as sound. Astronomers have used this fact to measure the speed of objects in space as they move away from Earth. They know the frequency and wavelength of the light as it leaves a star because the energy transitions in atoms are the same throughout the universe. When the light reaches Earth, it has a different frequency from when it left the star. 6. Assess how the knowledge that light always travels at the same speed is essential for determining the speed at which a distant galaxy and Earth are moving apart.

Reading Skills 6. Assess how the knowledge that light always travels at the same speed is essential for determining the speed at which a distant galaxy and Earth are moving apart. Answer: Using the change in frequency of light and the fact that the speed of light is constant, astronomers can calculate how fast the objects are moving away from one another.

Reading Skills The Doppler Effect applies to light as well as sound. Astronomers have used this fact to measure the speed of objects in space as they move away from Earth. They know the frequency and wavelength of the light as it leaves a star because the energy transitions in atoms are the same throughout the universe. When the light reaches Earth, it has a different frequency from when it left the star. 7. Astronomers have observed that the wavelength of light reaching Earth from one edge of the sun is slightly different than from the other edge. What can be concluded about the sun based on this observation?

Reading Skills 7. Astronomers have observed that the wavelength of light reaching Earth from one edge of the sun is slightly different than from the other edge. What can be concluded about the sun based on this observation? Answer: The observation indicates that the sun is rotating. The light from one edge is shifted to a shorter wavelength, and light from the other edge is shifted to a longer wavelength.

$Interpreting Graphics 8. What wave phenomenon is demonstrated in this illustration? A. diffraction C.$

Interpreting Graphics 8. What wave phenomenon is demonstrated in this illustration? A. diffraction C. reflection B. Interference D. refraction

$Interpreting Graphics 8. What wave phenomenon is demonstrated in this illustration? A. diffraction C.$

Interpreting Graphics 8. What wave phenomenon is demonstrated in this illustration? A. diffraction C. reflection B. Interference D. refraction

Interpreting Graphics 9. Which of the points on the illustration indicates an antinode? F. W H. Y G. X I. Z

Wave Properties • Light comes in a wide range of frequencies and wavelengths. • Our eyes can detect light with frequencies ranging from about 4. 3 1014 Hz to 7. 5 1014 Hz. • Light in this range is called visible light. • The full range of light at different frequencies and wavelengths is called the electromagnetic spectrum.