Waves
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Waves Energy can be transferred by either 1) Matter(mass) ex) baseball, electron
Waves Energy is transferred by 2) Waves ex) sound, radio, water, light
Waves
Waves transfer energy not mass.
Notice that all the matter is in the same location after the wave has passed.
Wave Types 1.
Mechanical Waves These waves need a medium. The material that the wave travels through is called the medium.
1. Mechanical Waves ex) water waves travel through _______ sound waves travel through ______ slinky waves travel through _________
2. Electromagnetic Waves EM waves do not need a medium. Ex) radio, TV, microwave, X-rays, visible light
4 types of Mechanical Waves
1. Transverse Waves 2. Longitudinal Waves 3. Torsional Waves - twist 4. Surface Waves – water at the ocean
Transverse Waves
1. Transverse Waves
The particles in the medium vibrate perpendicular to the direction the waves are traveling.
Transverse Waves Examples – water waves, slinky waves, Wave characteristics – 1) wavelength = λ the horizontal distance between corresponding points on consecutive waves. λ
HITT- What two sets of points are in one wavelength apart ? B A
G
C D
F E
H
Ans - A and F
B A
C and H
B and G
G
C D
F E
H
Transverse Waves Wave characteristics – 2) amplitude = A the distance from the rest position to the maximum displacement. A A
Transverse Waves
Examples – water waves, slinky waves,
Wave characteristics – 3) crest = maximum displacement UP 4) trough = maximum displacement DOWN
Amplitude vs Energy Q - With a slinky, how do you make a pulse with a larger amplitude?
Amplitude vs Energy A – Add more energy by swinging the rope harder. The amplitude is directly proportional to the energy.
Moving up or down?
You must be able to determine whether the molecules in a medium are moving up or down as the pulse - crest or trough - moves forward.
A
In Phase
Two points in a wave are said to be in phase if they have
a) the same amplitude and b) are moving in the same direction(either both up or both down)
HITT - What two sets of points are in phase ?
B A
C
F
G H
D E
Ans – B and F
B A
D and H
C
F
G H
D E
Mechanical Waves
2. Longitudinal Waves The particles move parallel to the direction the waves are traveling.
Longitudinal Waves Compressions – regions where the medium is more dense – the material is packed tightly. Rarefactions – regions where the medium is less dense – the material is spread out.
Describing Waves
Frequency, f is the number of wavelengths that pass a given point each second.
Unit = Hertz, Hz or cycles per second or waves per second or 1/s or s-1
The period, Τ, is the time for one wave to pass. Units - seconds The period is the inverse of frequency. Τ = 1/f or f = 1/ Τ Usually the frequency is determined by the source, the person shaking the slinky.
HITT Practice f and T
HITT – The periodic wave has 20 crests pass by in 5 seconds. The frequency is a) 20 hz b) 5 hz c) 4 hz d) 0.25 hz The period is a) 20 s b) 5 s c) 4 s d) 0.25 s
The velocity of pulses The velocity of waves is also called the speed of propagation. V = d/t d is the distance the pulse travels. t is the time.
The velocity of pulses
A second method to determine the speed of the pulse.
V=fλ Units 1/s x m or m/s
Speed of waves
The speed depends upon the medium in which the wave travels regardless of the frequency or wavelength or amplitude.
If different frequencies had different speeds, music would become jumbled as it traveled from the source.
Relationship between f, λ, and v 1st – v does not affect f or λ 2nd – As f increases, λ decreases this is an inverse relationship. Or as f decreases, λ increases. More pulses per second means the waves will be closer together.
Reflection of Pulses
What happens when a pulse hits a new medium? The new medium could be a new spring, a wall, etc.
The new medium can be more dense – like a wall or less dense like air. This determines whether the reflection will be inverted or erect.
Reflection of Pulses Remember the new medium will have a wave with a different velocity and a different wavelength but the same frequency. The reflected pulse will be erect if the new medium is less dense. The reflected pulse will be inverted if the new medium is more dense. The transmitted pulse is always erect.
Reflected – Transmitted What happens at the boundary between media?
When the pulse strikes the boundary, some of the energy is reflected as a reflected pulse and some continues on as a transmitted pulse.
Reflected – Transmitted What happens at the boundary between media?
The amount of reflected pulse depends upon the difference between their properties. If the two mediums are identical, then all the energy is transmitted.
Q - Is the new frequency different? A – No, since the pulse was produced by the same source, it must have the same frequency. But it is a new medium, therefore a new velocity and so a new wavelength.
Entering a new medium
If v decreases, the λ decreases. As the waves slow down, the crests get closer together.
Entering a new medium If v increases, the λ increases. As the waves speed up, the crests get farther apart. Since v = fλ for both mediums and the frequencies are the same V = f λ and v = f λ 1 1 1 2 2 2 and since f1 = f2 Then v /λ = v /λ 1 1 2 2
Interference What happens to pulses when they hit each other? Waves are not changed by passing through each other.
Interference
When we superimpose one pulse on top of another it is called superposition.
Interference Constructive
interference a crest meets a crest or
Interference Constructive
interference a trough meets a trough
Interference Destructive
interference a crest meets a trough
Waves Energy is transferred by 2) Waves ex) sound, radio, water, light
Waves
Waves transfer energy not mass.
Notice that all the matter is in the same location after the wave has passed.
Wave Types 1.
Mechanical Waves These waves need a medium. The material that the wave travels through is called the medium.
1. Mechanical Waves ex) water waves travel through _______ sound waves travel through ______ slinky waves travel through _________
2. Electromagnetic Waves EM waves do not need a medium. Ex) radio, TV, microwave, X-rays, visible light
4 types of Mechanical Waves
1. Transverse Waves 2. Longitudinal Waves 3. Torsional Waves - twist 4. Surface Waves – water at the ocean
Transverse Waves
1. Transverse Waves
The particles in the medium vibrate perpendicular to the direction the waves are traveling.
Transverse Waves Examples – water waves, slinky waves, Wave characteristics – 1) wavelength = λ the horizontal distance between corresponding points on consecutive waves. λ
HITT- What two sets of points are in one wavelength apart ? B A
G
C D
F E
H
Ans - A and F
B A
C and H
B and G
G
C D
F E
H
Transverse Waves Wave characteristics – 2) amplitude = A the distance from the rest position to the maximum displacement. A A
Transverse Waves
Examples – water waves, slinky waves,
Wave characteristics – 3) crest = maximum displacement UP 4) trough = maximum displacement DOWN
Amplitude vs Energy Q - With a slinky, how do you make a pulse with a larger amplitude?
Amplitude vs Energy A – Add more energy by swinging the rope harder. The amplitude is directly proportional to the energy.
Moving up or down?
You must be able to determine whether the molecules in a medium are moving up or down as the pulse - crest or trough - moves forward.
A
In Phase
Two points in a wave are said to be in phase if they have
a) the same amplitude and b) are moving in the same direction(either both up or both down)
HITT - What two sets of points are in phase ?
B A
C
F
G H
D E
Ans – B and F
B A
D and H
C
F
G H
D E
Mechanical Waves
2. Longitudinal Waves The particles move parallel to the direction the waves are traveling.
Longitudinal Waves Compressions – regions where the medium is more dense – the material is packed tightly. Rarefactions – regions where the medium is less dense – the material is spread out.
Describing Waves
Frequency, f is the number of wavelengths that pass a given point each second.
Unit = Hertz, Hz or cycles per second or waves per second or 1/s or s-1
The period, Τ, is the time for one wave to pass. Units - seconds The period is the inverse of frequency. Τ = 1/f or f = 1/ Τ Usually the frequency is determined by the source, the person shaking the slinky.
HITT Practice f and T
HITT – The periodic wave has 20 crests pass by in 5 seconds. The frequency is a) 20 hz b) 5 hz c) 4 hz d) 0.25 hz The period is a) 20 s b) 5 s c) 4 s d) 0.25 s
The velocity of pulses The velocity of waves is also called the speed of propagation. V = d/t d is the distance the pulse travels. t is the time.
The velocity of pulses
A second method to determine the speed of the pulse.
V=fλ Units 1/s x m or m/s
Speed of waves
The speed depends upon the medium in which the wave travels regardless of the frequency or wavelength or amplitude.
If different frequencies had different speeds, music would become jumbled as it traveled from the source.
Relationship between f, λ, and v 1st – v does not affect f or λ 2nd – As f increases, λ decreases this is an inverse relationship. Or as f decreases, λ increases. More pulses per second means the waves will be closer together.
Reflection of Pulses
What happens when a pulse hits a new medium? The new medium could be a new spring, a wall, etc.
The new medium can be more dense – like a wall or less dense like air. This determines whether the reflection will be inverted or erect.
Reflection of Pulses Remember the new medium will have a wave with a different velocity and a different wavelength but the same frequency. The reflected pulse will be erect if the new medium is less dense. The reflected pulse will be inverted if the new medium is more dense. The transmitted pulse is always erect.
Reflected – Transmitted What happens at the boundary between media?
When the pulse strikes the boundary, some of the energy is reflected as a reflected pulse and some continues on as a transmitted pulse.
Reflected – Transmitted What happens at the boundary between media?
The amount of reflected pulse depends upon the difference between their properties. If the two mediums are identical, then all the energy is transmitted.
Q - Is the new frequency different? A – No, since the pulse was produced by the same source, it must have the same frequency. But it is a new medium, therefore a new velocity and so a new wavelength.
Entering a new medium
If v decreases, the λ decreases. As the waves slow down, the crests get closer together.
Entering a new medium If v increases, the λ increases. As the waves speed up, the crests get farther apart. Since v = fλ for both mediums and the frequencies are the same V = f λ and v = f λ 1 1 1 2 2 2 and since f1 = f2 Then v /λ = v /λ 1 1 2 2
Interference What happens to pulses when they hit each other? Waves are not changed by passing through each other.
Interference
When we superimpose one pulse on top of another it is called superposition.
Interference Constructive
interference a crest meets a crest or
Interference Constructive
interference a trough meets a trough
Interference Destructive
interference a crest meets a trough
