Waves Note Packet - Hicksville Public Schools / Homepage

Physics R
Date: __________________
Review Questions
1. A ball dropped from rest falls freely until it hits the ground with a speed of 20 meters per second. The
time during which the ball is in free fall is approximately
2. In a flashlight, a battery provides a total of 3.0 volts to a bulb. If the flashlight bulb has an operating
resistance of 5.0 ohms, the current through the bulb is
Waves
Waves transfer energy without transferring matter
A pulse is a single disturbance
A periodic pulse creates a wave
Two groups of waves
1. Mechanical waves – sound, ocean waves, etc.
2. Electromagnetic waves – light, radio, microwaves, x rays, etc.
Waves can be transverse or longitudinal
Transverse Waves
The vibration or motion of a particle is perpendicular to the motion of the wave
Examples of transverse waves: Ocean waves, Electromagnetic (EM) waves, strings
Longitudinal Waves
The vibration or motion of the particle is parallel to the motion of the wave
Examples of longitudinal waves: Sound
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Longitudinal Waves
Characteristics of periodic waves
Period –
Frequency –
Amplitude –
Wavelength –
Speed of a wave –
3. What is the period of a 60.-hertz electromagnetic wave traveling at 3.0 × 108 meters per second?
4. A wave completes 5 cycles in 2 seconds over a distance of 3m.
a) What is the wavelength?
b) What is the frequency?
c) What is the period?
d) What is the speed of the wave?
5. What is the frequency of a wave with a wavelength of 500 meters if it travels at a velocity of 25
meters per second? What is its period?
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Review Questions
6. What is the magnitude of the centripetal force on a 2.0 x 103 kg car as it goes around a 25 meter curve
with an acceleration of 5 m/s??
7. A 0.5 kg ball is thrown vertically upward with an initial kinetic energy of 25 joules. Approximately
how high will the ball rise?
Simple Harmonic Motion – Masses go to and fro
Oscillation – a periodic variation from one state to another
Simple harmonic oscillator – an object that repeats a period motion
Question:
A pendulum completes 10 swings in 15 seconds.
What is the period (T) of the pendulum in seconds?
What is the frequency (f) of the pendulum in Hz?
Potential energy
Kinetic energy
Total Energy
Question:
A mass on a spring oscillates at 3.2 Hz.
What is the period of the system (in seconds)?
How long will it take the system to complete 120 oscillations?
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Pulses – Wave Building Blocks
A pulse is a single vibratory disturbance that transfers energy but NOT mass.
Amplitude is the height of a pulse above equilibrium – shows ENERGY
A medium is a continuum of particles of a single type
ex: Water, air, metal rod, etc.
The medium stores then releases energy as pulses travel through it.
When pulses change mediums, they are
Interference
Pulses that encounter one another in a medium interfere
Pulse amplitudes are added together using the principle of superposition
Two types of interference:
Constructive Interference
Occurs when amplitude of two pulses is in the same direction
Energy of the two pulses is added together to produce a higher amplitude
Destructive Interference
Occurs when pulse amplitudes are in opposite directions
ENERGY of the two pulses partially or completely cancel out to produce a lower amplitude.
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Review Questions
8. If 10 coulombs of charge are transferred through an electric circuit in 5.0 seconds, then the current in
the circuit is
9. In driving down a hill a car loses 500 joules of potential energy but gains 1500 joules of kinetic
energy. If the work done to overcome friction was 200 joules, determine the total work done by the
engine to go down the hill.
10. In a flashlight a battery provides a total of 3.0 volts to a bulb. If the flashlight bulb has an operating
resistance of 5.0 ohms, the current through the bulb is
Sound Waves
A speaker pushes air forward and backward. The sound wave travels until it reaches your ear.
What type of wave is the sound wave?
Through what medium is the sound travelling?
What would happen to a sound wave in a vacuum?
The amplitude of the sound wave is also the:
Sound travels through air at 331 m/s (Find me on the reference table!)
Sound travels faster through denser mediums:
Speed of sound in water
Speed of sound in steel
Humans can hear sound from 20 Hz to 20kHz. Frequency =
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11. At STP, sound with a wavelength of 1.66 meters has a frequency of:
12. Middle C has a frequency of 262 Hz. What is the wavelength of middle C in air?
13. What is the wavelength of middle C in water?
14. If the speed of a wave doubles, its wavelength will be:
15. What is the period of a sound wave with frequency 600 Hz?
16. If the period of a sound wave is doubled, its frequency will be:
17. A sound wave with period 5.5 x 10-2 s is travelling through the air. What is the wavelength of the
sound wave?
18. How much time does it take light from a flash camera to reach a subject 6.0 meters across a room?
19. You see lightning, and 5 seconds later you hear thunder. How far away from you did the lightning
strike?
20. Mr. Vigneaux yells “Echo” across the grand canyon. 2.5 seconds later, he hears his echo. What is
the width of the canyon where he is yelling?
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Review Questions
21. When 800 joules of work are done on an object, its potential energy increases by 300 joules and its
kinetic energy increases by 400 joules. What was the work done against friction?
22. In a series circuit containing two lamps, the battery supplies a potential difference of 1.5 volts. If
the current in the circuit is 0.1 amperes, at what rate does the circuit use energy?
Wave Interference
Waves are superimposed like pulses
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Resonance
• Resonance occurs when a medium is vibrated near its _________________________
• Constructive interference occurs to an extreme degree causing vibrations with huge amplitude
• If the vibration has enough energy and the correct frequency, the medium may be damaged or
destroyed!
Examples of resonance:
 When you push somebody on a swing, you push with the same frequency as the swing to get
maximum amplitude
 Color is due to incoming light matching the natural frequency of electrons orbiting the proton in
an atom
 Instruments create a standing wave at a natural frequency to create a note. Some instruments
allow you to change the length of the instrument to change the frequency and allow more notes!
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Review Questions
23. What is the approximate electrostatic force between two protons separated by a distance of
1.0 x 10-6 meter?
24. What is the total resistance of this circuit?
Wave Fronts
A wave front is made up of all points on a wave that are vibrating in phase (in unison)
Wave fronts are separated by one wavelength.
Rays can be used to represent the direction that a wave is travelling in.
Rays are drawn perpendicular to wave fronts.
The Doppler Effect
The apparent change in the _____________________ of a wave when the source and observer are
moving relative to one another
• When the source and observer are approaching each other, the observed frequency is _____________
than the actual frequency of the wave.
• When the source and observer are moving away from each other, the observed frequency is
______________ than the actual frequency of the wave.
• Note that this change in frequency is only apparent. The actual frequency of the wave depends only
on the ___________________
• For light the Doppler shift is observed as a __________________ (higher apparent frequency) or
________________ (lower apparent frequency
All waves that reach a boundary can be reflected, refracted (transmitted), absorbed, and/or scattered.
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Reflection
A wave that reaches a boundary can be reflected
Light – mirror
Sound – echo
Law of reflection: (NOTE: All angles are measured from the normal to the surface)
Refraction (transmission)
When a wave enters a new medium, there is a change in angle of the wave due to the change in speed.
Medium is the material through which a wave is travelling (air, glass, water, etc.)
Fast medium to slow medium
Wave bends
Slow medium to fast medium
Wave bends
Wave incident along the normal – change in ______________ but no change in _____________
Change in speed of the wave results in a change in _____________________. The
____________________ of the wave is unchanged! (Depends only on the source creating the wave)
Diffraction
The _____________ of a wave to travel around corners, obstacles, or openings in its path
How much a wave diffracts depends on how the wavelength compares to the size of the opening
(smaller opening, more diffraction)
Huygen’s Principle: Every point on the wave acts as a new point source
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Review Checklist
Use equations to determine wave speed, wavelength,
period, or frequency. Understand the difference between
longitudinal and transverse waves. Explain how
amplitude and wavelength are measured. Explain the
concept of ‘phase’. Explain the direction of particle
motion in a medium.
1. What is speed of a wave with a frequency of 10 hertz
if its wavelength is 3 meters?
7. Determine the direction in which each particle shown
in the diagram will move in the next instant of time if the
wave moves to the right.
2. What is the wavelength of a wave with a frequency of 6
hertz if it is moving at 30 meters per second?
Explain the phenomenon of wave interference. Explain
the origin of and describe features of standing waves.
Explain the phenomenon of resonance
8. Sketch a wave that will completely destructively
interfere with the wave shown below.
3. What is the frequency of a wave that is moving at 15
meters per second if its wavelength is 7.5 meters? What is
this wave’s period?
4. Mark each diagram or statement with a “T” if it
describes a transverse wave or an “L” if it describes a
longitudinal wave.
9. At the point when the two waves shown below
completely overlap, what will the superposition of the two
waves look like? Draw a sketch of the wave produced
during this interaction.
10. Determine the wavelength of the standing wave
shown below. Identify one node and one anti-node.
5. What is the wavelength of each of the waves shown
below?
Explain the origin of sound waves, the conditions
necessary for them to exist and details regarding their
transmission. Explain the motion of objects in Doppler
Effect diagrams. Explain frequency changes due to the
Doppler Effect
11. If a ship sends a sonar signal through the water to the
sea floor and it bounces back to arrive back at the ship in
2.0 seconds, how deep is the water under the ship if sound
travels through water at 1500 meters per second?
6. What is the amplitude of each of the waves shown
below?
12. If it takes a sound wave 2.5 seconds to travel from the
spot where a lightning strike occurs to an observer, how
far away from the observer did the strike occur?
13. Why would an astronaut not be able to communicate
with another astronaut by talking in the vacuum of space?
14. A sound wave with wavelength 0.5 meters travels
through the air at STP. What is the frequency of the
sound wave?
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15. The diagram below shows a source of sound waves
moving with a constant speed near an observer. The
source produces sound waves with a frequency of 100
hertz.
Is the source getting closer to the observer or farther
away?
Which frequencies could the observer be hearing as the
source approaches?
(a) 80 Hz (b) 100 Hz (c) 110 Hz (d) 120 Hz
Describe the phenomenon of reflection; identify and
sketch wave front diagrams in which reflection occurs.
Explain why waves refract; identify and sketch wave front
diagrams in which refraction occurs. Explain the
diffraction of waves. Identify and sketch wave front
diagrams in which diffraction occurs.
16. The diagram below shows a series of wave fronts
approaching a barrier. Sketch a set of reflected wave
fronts on the diagram.
17. In which area of the diagram below is the wave
traveling more quickly?
Answers:
1. 30 m/s
2. 5 m
3. 2 Hz, 0.5 s
4. LT
LT
5. 2 m, 6 m
4 m, 0.8 m
3m
6. 0.25 m, 2 m
7. Down, up, up, down, up
8.
9.
10.
11.
12.
13.
14.
15.
2.5 m, NANANANAN
1500 m
828 m
Sound requires a medium (like air) to travel
662 Hz
Getting closer
c or d
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17. Area 1 (wavelength is greater, it is moving
faster)
18. Diffraction is most pronounced in the 3rd
example
18. Waves are diffracted as they pass through openings
or around barriers. Sketch the diffraction pattern in each
of the three cases shown below. In which case is the
diffraction most pronounced?
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