Download Waves (General Properties and Sound)pdf

印尼慈濟學校
TZU CHI SCHOOL
Waves
(Sound and Light Contexts)
Statement of Inquiry
The interaction of particles and energy produces patterns in
nature, and we use the relationship among those patterns to
study our world at a range of scales, from the atomic to
galactic.
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Summative Tasks
Criteria A- Knowing and
understanding
Unit Test
Explain knowledge of wave
phenomena, apply that knowledge to
solve problems in familiar and
unfamiliar situations, and analyze and
evaluate information.
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Criterion B -Inquiring and designing
Criterion C-Processing and
evaluating
Lab Report
Design, conduct, and evaluate an
independent investigation into one
factor influencing the refraction,
diffraction, or diffusion of sound or
light.
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Learning Targets (1)
1. Summarize examples of oscillations.
2. State that progressive (travelling) waves transfer energy.
3. Describe the terms crest, trough, compression, and
rarefaction.
4. Define the terms displacement, amplitude, frequency,
period, wavelength, wave speed, and intensity.
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Starter Activity
Assess what you already know about sound and light waves.
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Question 1
Describe the movement
(or the motion) of the
objects shown in the gif
animation.
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Oscillations
Regular, repeating back and forth motion of an object
Periodic Motion
A motion that is regular
and repeating
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Properties of Oscillation
Physical properties of objects undergoing a regular repeating pattern
Period, T
The time for an object to complete one cycle
(or oscillation), measured in seconds.
Frequency, f
The number of complete cycles occurring
per period of time, measured in Hz (Hertz).
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Properties of Oscillation
Physical properties of objects undergoing a regular repeating pattern
Amplitude, Xo
The maximum displacement of an object
from its resting position
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Example 1
A child on a swing performs 0.2 oscillations per second.Calculate the
period of the child's oscillations.
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Motion of an Oscillator
Watch the 40-s video clip.
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What did you notice in the animation?
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Motion of an Oscillator
The motion of oscillator can be observed through a simple mass and spring system.
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The oscillations will produce a curved, periodic
graph (sinusoidal trace).
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Motion of an Oscillator
The motion of oscillator can be observed through a simple mass and spring system.
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The oscillations will produce a curved, periodic
graph (sinusoidal trace).
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Formative Practice Task
Hooke’s Law: Mass on a Spring
1. Add various masses to a spring.
2. Observe the effect on amplitude and period of the
oscillations.
3. Suggest a relationship among the mass, amplitude
and period based on your observations.
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Formative Practice Task
Hooke’s Law: Mass on a Spring
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Formative Practice Task
Hooke’s Law: Mass on a Spring
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Formative Practice Task
Hooke’s Law: Mass on a Spring
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Formative Practice Task
Hooke’s Law: Mass on a Spring
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Formative Practice Task
Hooke’s Law: Mass on a Spring
As the mass increases, the period increases and the
frequency decreases.
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Check for Understanding
Formative, Criterion A (Level 1-2, 3-4)
1. State the relationship between period and frequency of an
oscillation.
2. Predict how the frequency would change if the period of
oscillation decreases.
3. Predict how the period of oscillation would change if frequency
decreases.
4. Calculate the period if frequency is 0.01 Hz.
5. Calculate the frequency if period is 10 s.
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Energy in Waves
Stretching Activity: Mexican Wave
1. Everybody gather in circle.
2. Do the Mexican wave.
3. Observe any kind of motion.
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Energy in Waves
Energy is transferred through a wave, but matter is not.
Wavefront
The points in a wave that vibrate in unison.
Pulse
A single disturbance that moves through a
medium from one point to the next point
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The direction of the motion of the wave is the direction of the
energy transfer.
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Energy in Waves
Energy is transferred through a wave with no displacement of matter.
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Energy in Waves
Describe the motion of the
particles. (Hint: Did they go
anywhere?)
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Energy in Waves
The particles just move in repeating
cycles–they don’t actually go anywhere.
There is no net displacement of matter.
The wavefront moves from top left to
bottom right.
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Check for Understanding
Describe (give a detailed account) how the image below illustrates the
transfer of energy through a travelling wave.
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Check for Understanding
Describe (give a detailed
account) how the image below
illustrates the transfer of energy
through a travelling wave.
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The particles involved in waves move back
and forth perpendicularly to the way the
wave is going, but don’t move significantly in
the direction of the wave.
The particles ‘take part’ in the wave by
bumping into one another and transferring
energy.
This is why energy can be transferred, even
though the average position of the particles
doesn’t change.
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Wave Energy Summary
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Transverse Wave
Crest
the point of maximum positive (or
upward) displacement from the
rest position
Trough
the point of maximum negative
(or downward) displacement
from the rest position
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Transverse waves include water and electromagnetic waves
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Anatomy of a Wave
Wave diagrams let us visualize the periodic motion and energy of oscillations.
Wavelength, λ (m),
the distance from one point in a
wave to the same point in the next
wave
Displacement, x (m),
the distance a particle is from
equilibrium position
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Anatomy of a Wave - Checkpoint 1
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Anatomy of a Wave - Checkpoint 1
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Check for Understanding
Formative, Criterion A (Level 1-2, 3-4)
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1. Which letter(s) represent(s) the wavelength?
2. Which letter(s) represent(s) the amplitude?
3. Outline how “C” and “E” relate to wavelength.
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Waves on a Graph
Wave diagrams let us visualize the periodic motion and energy of oscillations.
A displacement-position graph
shows the displacement of the
particles at various positions at a
certain time.
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Wavelength and Amplitude can be read from this graph.
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Waves on a Graph
Wave diagrams let us visualize the periodic motion and energy of oscillations.
A displacement-time graph
describes the displacement of
ONE particle at various times at
a certain position.
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Time Period and Amplitude can be read from this graph.
Frequency can be calculated.
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Waves on a Graph - Checkpoint - 1
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Determine a) the amplitude A of the wave in meters; and
b) the frequency of the wave in Hertz.
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Waves on a Graph - Checkpoint - 2
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Waves on a Graph - Checkpoint - 2
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Intensity: Other Wave Property
The amplitude of waves indicate their intensity (energy).
Intensity of a wave is defined
as the power per unit area. It
has units of Wm-2.
The amplitude of a wave varies in a sinusoidal manner with time whereas the
intensity of the wave varies as sine squared.
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I𝛼A
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Longitudinal Wave
Compression
A point of maximum density in
the medium through which a
longitudinal wave moves
Rarefaction
A point of minimum density in the
medium through which a
longitudinal wave moves
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Longitudinal waves include sound and earthquake pressure waves.
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Longitudinal and Transverse Waves
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Wave Types - Checkpoint 1
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Wave Types - Checkpoint 1
Parallel to the direction of wave travel
Sound waves
Perpendicular to the direction of wave travel Light waves
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Wave Types - Checkpoint 2
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Wave Types - Checkpoint 3
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The Wave Equation
Frequency, velocity, and wavelength are intimately linked.
Distance• The distance travelled by one complete
Speed =
wave is λ (m)
Time
•
v =λ
T
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The time taken for one complete wave to
pass is T (s)
Substitute the reciprocal relationship
The Wave Equation
v = fλ
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The Wave Equation
v = fλ
For a wave of constant
speed:
• As the wavelength
increases, the frequency
decreases
• As the wavelength
decreases, the frequency
increases
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The Wave Equation - Checkpoint 1
Applies to water waves, light and other electromagnetic waves,
and sound waves.
Example:
Some water waves in a ripple tank have a frequency of 2 Hz and a
wavelength of 5 cm. What is their speed?
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The Wave Equation - Checkpoint 2
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The Wave Equation - Checkpoint 2
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Check for Understanding
Formative, Criterion A (Level 1-2, 3-4)
Command Term: State → brief answer without explanation or calculation
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1. State the impact on the wavelength if the frequency of a
wave traveling at constant velocity is increased.
2. State the impact on the frequency if the velocity is increased
of a wave of constant wavelength.
3. State the impact on the velocity of a wave if the frequency of
a constant wavelength is increased.
4. State the impact on the velocity of a wave if the period of
the wave is increased. Assume a constant wavelength.
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Check for Understanding
Formative, Criterion A (Level 3-4, 5-6)
The worksheet/homework is uploaded in Google classroom.
Write your complete working in your notebook.
Notebooks may be collected for marking.
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Sound Wave
Sound is a longitudinal wave, as such, require a medium in
which to propagate.
Sound waves are generated
by oscillating sources, which
produce a change in density
of the surrounding medium.
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Sound Wave
Humans can hear sounds between about 20 Hz and 20 000 Hz in frequency
(although this range decreases with age).
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Sound Wave
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Sound Wave
● Sound waves require a medium to travel through
If there are no molecules (e.g. in a vacuum) then the sound can’t
travel.
● The loudness of a sound is related to the wave’s amplitude
(Greater amplitude = louder sound)
● The pitch of a sound is related to the frequency
(Greater frequency = higher pitch)
● As with all waves, sound waves can be reflected
The reflection of a sound wave is called an echo
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Sound Wave - Checkpoint 1
Two sounds are produced by loudspeakers. The parameters of
these sounds are given in the table below. In terms of loudness and
pitch, compare Sound 1 with Sound 2.
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Sound Wave - Checkpoint 1
Two sounds are produced by loudspeakers. The parameters of these
sounds are given in the table below. In terms of loudness and pitch,
compare Sound 1 with Sound 2.
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Sound Wave - Checkpoint 2
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Sound Wave - Checkpoint 2
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Sound Wave - Checkpoint 3
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Sound Wave - Checkpoint 3
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Check for Understanding
Formative, Criterion A (Level 3-4)
The worksheet is uploaded in the Google classroom.
Work on it independently.
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Check for Understanding
Formative, Criterion A (Level 3-4)
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Experiment
Formative (Open Lab)
Criterion B - Inquiring and Designing
Criterion C - Processing and Evaluating
Idea
Question
Task
:The speed of sound in air is 340 m/s.
:How can we measure the speed of sound experimentally?
:Plan an investigation to accurately measure the speed of
sound using equipment found in the laboratory and the
school's grounds.
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Experiment
Formative
Criterion B - Inquiring and Designing
For criterion B, you will formulate a testable hypothesis and explain it using
scientific reasoning; explaining how to manipulate the independent variable
and collect the associated dependent variable while controlling external
factors.
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Experiment
Formative
Criterion C - Processing and Evaluating
For criterion C, you will collect and transform data from the experiment,
interpret this data, and explain results using scientific reasoning by
evaluating the original hypothesis’s validity based on the investigation’s
outcome and discuss improvements or extensions to the method.
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