Sound and Light
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Transcript of Sound and Light
Sound and Light
Chapter 1: Characteristics of Waves
Section 1: What are Waves3: 38.08/58 = 60.48%
5: 46.05/58 = 79.40%
6: 45.80/58 = 78.97%
Vocabulary
Wave Energy Medium Mechanical Wave Vibration Transverse wave
Crest Trough Longitudinal wave Compression Rarefaction
Waves and Energy A wave is a disturbance that transfers energy from
place to place. Remember, energy is the ability to do work. Think about a raft on the water
Wave disturbs surface as well as raft. But the disturbance caused by the wave is temporary, and the wave passes, and raft returns to normal.
Most kinds of waves require something to travel though. The material through which a wave travels is called a
medium. Waves that require a medium are called mechanical
waves. Waves that don’t require a medium are called
electromagnetic waves
How do waves transfer energy?
Although mechanical waves travel though a medium, they don’t carry the medium with them.
The wave just makes the medium move back and forth, it is the energy that is getting transferred. Think of the “wave” at a sporting event
What causes waves?
Energy is always required to make a wave. Mechanical waves are produced when a
source of energy causes a medium to vibrate. A vibration is the repeated back and forth or up
and down motion. When a vibration moves through a medium, a
wave results. Remember, anything that moves has energy,
so a moving object can give its energy to a medium, and make a wave.
Types of Waves Transverse Waves
Waves that move the medium at right angles to the direction the wave travels.
As a transverse wave moves, the particles of the wave move at right angles to the direction of the wave.
Longitudinal Waves These waves move the medium parallel to the
direction in which the wave travels. Compression is where the medium is close
together Rarefactions are where the medium is far
apart.
We can use diagrams to represent transverse and longitudinal waves.
Sound and Light
Chapter 1: Characteristics of Waves
Section 2: Properties of Waves
Vocabulary
Amplitude Wavelength Frequency
Amplitude Remember, all mechanical waves move medium. The distance the medium moves depends upon the
amplitude. Amplitude is the maximum distance that the
particles of the medium carrying the wave move away from their rest positions.
More energy = Greater Amplitude For transverse waves: Amplitude is the maximum distance
up or down the wave moves. Higher/lower waves = greater amplitude
For longitudinal waves: Amplitude is the measure of how compressed or rarefied the medium becomes. Dense compressions = greater amplitude
Wavelength
Wavelength A wave travels a certain distance before it starts
to repeat. The distance between two corresponding parts of
a wave is the wavelength. Transverse Wave: Wavelength can be found by
measuring distance from crest to crest or from trough to trough.
Longitudinal Wave: Wavelength can be found by measuring distance between compressions.
Frequency
Wave frequency is the number of complete waves that pass any given point in a certain amount of time. If I make waves in a rope so that one wave
passes a given point every second, the frequency of the wave is 1 wave per second.
Frequency is measured in unit of hertz (Hz) The wave above would have a frequency of 1 Hz.
Speed of Waves
Different waves travel at different speeds. The speed of a wave is how far the wave
travels in a given length of time Or the distance divided by the time it took to travel
that distance.
Relating Ideas
Speed, wavelength and frequency are mathematically related.
Speed = Wavelength x Frequency Wavelength = Speed / Frequency Frequency = Speed / Wavelength
Sound and Light
Chapter 1: Characteristics of Waves
Section 3: Interactions of Waves
Vocabulary Reflection Refraction Law of reflection Diffraction Interference Constructive Interference Destructive Interference Standing wave Node Antinode Resonance
Reflection
When a wave hits a surface though which it cannot pass, it bounces back. This interaction is called
reflection All waves obey this.
The law of reflection states that the angle of incidence equals the angle of reflection.
Refraction When a wave moves
from one material to another, it encounters a change in wave speed.
If the wave is at an angle, one side change speed before the other, causing it to bend.
This bending of waves due to a change in speed is called refraction. Again, the wave MUST
enter an angle for this to occur
White light and refraction
White light is made of lots of different frequencies of light
When white light refracts, each color bends by different amounts. This separates the colors Rainbows!
Diffraction
When a wave moves around a barrier or after it passes through a narrow channel it will bend and spread out. This is called diffraction.
Like refraction, it involves the bending of waves.
Unlike refraction, does not pass through any new materials.
Interference Interference is an interaction that occurs whenever two
waves meet. Two types of interferences
Constructive Interference Occurs when two waves combine to make a wave with a bigger
amplitude Occurs when crests of one wave overlap with crests of another
wave (or troughs and troughs) Destructive Interference
Occurs when two waves combine to make a wave with a smaller amplitude
Occurs when crests of one wave overlap the troughs of a 2nd wave. If crest is larger than trough, then resultant wave will have a smaller crest If trough is larger than crest, the resultant wave will have a smaller
trough
Interference Applets
Standing Waves
A special occurrence when interference occurs after wave reflection has occurred.
If the incoming wave and reflected wave have just the right frequency, they will produce a combined wave that appears to be standing still.
This combined wave is called a standing wave. So a standing wave is really two waves interfering
as they pass through each other, that appears to be standing still.
Nodes and Antinodes
In a standing wave, destructive interference produces points with no amplitude. These points of zero amplitude on a standing wave are
called nodes. Nodes are always evenly spaced on the standing wave.
Also in a standing wave, constructive interference creates points with great amplitude. These points of maximum amplitude are called antinodes. Antinodes are also ½ between nodes.
Standing Wave Demonstrator
Resonance Most object have a natural frequency.
A swing that is pushed at the swing’s natural frequency allows a small push to create a large increase in the swing’s amplitude.
Standing waves occur when an object vibrates at its natural frequency.
If a nearby object vibrates at the same frequency as an object’s natural frequency, resonance can occur. Resonance is an increase in the amplitude of a vibration
that occurs when external vibrations match an object’s natural frequency.
Can be useful Musical instruments use resonance o create stronger,
clearer sounds.
Resonance can be harmful Tacoma Narrows Bridge