waves gcse physics. objectives of the lesson understand the concept of wave motion in the physical...
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Waves
GCSE Physics
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Objectives of the Lesson
• Understand the concept of wave motion in the physical world
• Recall that there are two types of wave motion- Longitudinal and Transverse
• Explain the difference between the types of waves and use the correct terms for each
• State some examples of each of the types of wave motion
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Waves Introduction
• A wave can be described as a disturbance that travels through a medium from one place to another.
• Medium – a substance which something is transmitted or carried through e.g.. air
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Examples of waves
• Sea wave (medium- liquid, water)
• Shotgun blast (medium- gas, air)
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Types of Waves- TransverseWave motion vs Particle motion
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Watch one particle
Describe its motion
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Transverse wave…
In terms of the wavelength, what is the length of the red line on the graph?
Wavelength λ – distance from one point on one wave to the same point on the next wave (for example- from crest to crest)
CrestCrest CrestCrest
TroughTrough TroughTrough
Wavelength λWave spreadsWave spreads
Wave movementWave movement
Light travels as a transverse wave
Wave movement is at right angles to the direction that the wave is travelling
Amplitude – maximum displacement from its undisturbed position
Amplitude
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Types of Waves- Longitudinal Wave motion vs Particle motion
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Keep your eye on 1 particle
Describe its motion
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If the diagram shows the motion of the wave in 1 second then what is the frequency of the wave?
Frequency – the number of waves passing a point every second (Hz)
Longitudinal wave
Rarefaction Compression
Sound waves travel as longitudinal waves
Wave movement is parallel to the direction the wave is travelling
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Water Waves
• Water waves are an example of waves that involve a combination of both longitudinal and transverse motions. As a wave travels through the water, the particles travel in clockwise circles.
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Longitudinal Vs Transverse
• Create a table with two column headings, Longitudinal and Transverse
Wave motion is at right angles to the
direction of the wave
Wave motion is parallel to the direction of the wave
Amplitude is maximum displacement from the wave’s rest position
Frequency is the number of waves
passing a point in one second
Wavelength is the distance from one crest to the next
crest
Wavelength is the distance from one compression to the next compression
This is how sound energy moves
This is how light travels
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Graph action…
http://surendranath.tripod.com/Applets/Waves/Twave01/Twave01Applet.html
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Objectives of the Lesson
• Recall the wave equation and use it to solve simple problems
• Describe, using simple wavefront diagrams, how plane waves are reflected at a plane barrier, refracted at a plane boundary
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The Wave Equation
• Speed (v) = Frequency (f) x Wavelength (λ)
m/s Hz m
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Example
• What is the speed of a water wave of frequency 4 Hz and wavelength 3 cm?
v = f x λ
= 4 x (3 / 100)
= 0.12 m/s
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Try this one…
What is the wavelength of a sound wave of frequency 264 Hz and speed 330 m/s?
v = f x λ
330 = 264 x λ
λ = 330 / 264 = 1.25 m
What is the distance between one compression and the next rarefraction on this wave?
1.25 / 2 = 0.625 m
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Question Time
• Pg 105 Question 1 a) parts i) – iv)
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Objectives of the Lesson
• Describe, using simple wavefront diagrams, how plane waves are reflected at a plane barrier, refracted at a plane boundary
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Ripple Tank
Wave motion
Crest
Trough
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Wave Diagrams
• Law of Reflection- The angle of incidence is always equal to the angle of reflection
Wave front Wave front (crest)(crest)
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The angle the wave hits the barrier at is 23 degrees.
1. What is the angle of incidence?
2. Draw the three waves after they have hit the
barrier and label the angle of reflection and include the
normal line.
Example
23º
Normal line
Angle of incidence 67º
Angle of Angle of reflection 67reflection 67ºº
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Objectives of the Lesson
• Describe, using simple wavefront diagrams, how plane waves are reflected at a plane barrier, refracted at a plane boundary
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Shallow Shallow waterwater
Deep water
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• RefractionRefraction-- For a wave moving from deep to shallow, the wavelength will shorten because the wave slows down.
• The frequencyfrequency of the wave stays the same
Refraction
Shorter Shorter Wavelength- Wavelength- waves speed waves speed slowerslower
Shallow Shallow waterwater
Deep water
λ
λ
wavefront
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Refraction• If the incident wave travels at an angle and
meets shallow water, then the wave will be refracted (shifted) towards the normal
Angle of Angle of refractionrefraction
Angle of incidenceAngle of incidence
Normal line
Shallow water
Deep water
Angle of incidence Angle of refractionAngle of refraction>
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Refraction
• What do you think will happen when a wave travels into deeper water? Draw a diagram with labels to represent the situation.