Lecture 3: Waves, the Physics of Light & Sound Flashcards Preview

PSYCH 3310: Sensation & Perception > Lecture 3: Waves, the Physics of Light & Sound > Flashcards

Flashcards in Lecture 3: Waves, the Physics of Light & Sound Deck (63):
1

What is a wave?

Lights and sounds are composed of waves.

A wave is a type of internal motion of a medium, in which the displaced portion returns to equilibrium.

This disturbance propagates in space as well.

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Wave

disturbance propagates in x…

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Transverse Waves

This is what occurs in the vibrations of stringed instruments

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Longitudinal Waves

This is what occurs in the vibrations of wind instruments

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Types of Waves

Transverse Waves – This is what occurs in the vibrations of stringed instruments.

Longitudinal Waves – This is what occurs in the vibrations of wind instruments.

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Sound Waves

Sound waves involve the longitudinal oscillations of air molecules.

The sound vibrations in a long, narrow tube, such as a trombone, flute or trumpet, propagates in one direction.

In open air, a sound wave propagates radially in all directions

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Light Waves

Light waves involve transverse oscillations in electric and magnetic fields

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Light

A wave; a stream of photons, tiny particles that each consist of one quantum of energy

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Diagram of a wave

All waves are caused by vibrations

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Velocity, Frequency and Wavelength

Within a given medium, light & sound waves travel at a constant velocity.

Thus, long wavelengths oscillate at low frequencies, and short wavelengths oscillate at high frequencies.

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Long wavelengths oscillate at _____ frequencies.

low frequencies

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short wavelengths oscillate at ____ frequencies.

high frequencies

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Two waves with the same velocity and different wavelengths will have different frequencies.

Two waves with the same frequency and different wavelengths will have different velocities

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Two waves with the same frequency and different wavelengths will have different velocities

Two waves with the same velocity and different wavelengths will have different frequencies

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Interference

The addition and subtraction of waves

When 2 or more waves come together, the individual displacements at each point in space are added together to produce a composite wave.

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Absorption

The conversion of energy to a different form, such as heat, when a wave hits an obstacle

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Reflection

The reversal of direction when a wave hits an obstacle.

When a wave hits a boundary between two media, some of its energy rebounds in a different direction.

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Refraction

The bending of a wave as it crosses the boundary between two media

Refraction is what causes a pencil to appear bent when it is partially submerged in water.

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Diffraction

The bending of a wave around an obstacle

Waves can sometimes bend around obstacles.
Long wavelengths diffract more than short wavelengths.

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Wave Interactions

Interference – The addition and subtraction of waves.

Absorption – The conversion of energy to a different form, such as heat, when a wave hits an obstacle.

Reflection – The reversal of direction when a wave hits an obstacle.

Refraction – The bending of a wave as it crosses the boundary between two media.

Diffraction – The bending of a wave around an obstacle.

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When two or more waves come together, the individual displacements at each point in space are added together to produce a composite wave. This is referred to as ______.

interference

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When a wave hits a boundary between two media, some of its energy may be converted to heat.

This is an exmple of....

Absorption

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Scattered

Energy that is dispersed in an irregular fashion.

When light enters the atmosphere, much of it is absorbed or scattered and never reaches the perceiver.

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When a wave hits a boundary between two media, some of its energy rebounds in a different direction

Reflection

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Some animals, such as bats, are able to use reflections of sounds to determine ______ .

the distance of objects

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Energy that is passed on through a surface (when it is neither reflected nor absorbed by the surface) is called ......

Transmitted energy

When a wave hits a boundary between two media, some of its energy may be transmitted across the boundary

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Transmitted

Energy that is passed on through a surface (when it is neither reflected nor absorbed by the surface)

When a wave hits a boundary between two media, some of its energy may be transmitted across the boundary

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What happens to a wave when it changes speed

Refraction

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When a wave travels from a less dense to a more dense medium at an angle off the line of normal, it _____ and bends ______ the line of normal.

When a wave travels from a less dense to a more dense medium at an angle off the line of normal, it *slows down and bends *towards the line of normal.

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When a wave travels from a more dense to a less dense medium at an angle off the line of normal, it ____ and bends *away from the line of normal.

When a wave travels from a more dense to a less dense medium at an angle off the line of normal, it *speeds up and bends *away from the line of normal.

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____ wave lengths refract MORE than _____ wavelengths.

Short wave lengths refract MORE than long wavelengths.

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Rainbows are caused by light that is _____ through particles of water.

Rainbows are caused by light that is *refracted* through particles of water.

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_____ wavelengths diffract more than _____ wavelengths

Long wavelengths diffract more than short wavelengths

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This animation shows diffraction through a slit.

It also shows how interference patterns can occur when a wave interacts with its own reflection.

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Natural Frequencies

Most objects have a specific frequency at which they vibrate most readily. This is called the natural or fundamental frequency.

For a vibrating string, the natural frequency increases with the tension of a string, and decreases with increasing length or mass.

For a vibrating tube, the natural frequency decreases with increasing tube length, and is higher for open tubes than for closed tubes.

The manipulation of these parameters is what allows musicians to play musical instruments.

Rule to remember: Short things have higher natural frequencies than long things

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Rule to remember:

Short things have higher natural frequencies than long things

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Methods of representing waves

Waveform plots
Spectral plots
Spectrograms

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Spectrum plots

Amplitude against frequency

The amplitudes of the sine waves give the amplitude spectrum of the sound.

The amplitude spectrum of a sine wave is a single point at the frequency of the sine wave.

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Waveform

Amplitude against time

Sound is a change in the pressure of the air.
The waveform of any sound shows how the pressure changes over time.

The eardrum moves in response to changes in pressure.

Any waveform shape can be produced by adding together sine waves of appropriate frequencies, amplitudes and phases.

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Sound is ....

....a change in the pressure of the air.

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The amplitudes of the sine waves give the amplitude spectrum of the sound.

The amplitude spectrum of a sine wave is a single point at the frequency of the sine wave.

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Amplitude is a measure of the pressure change of a sound and is related to how loud the sound is.

Amplitude squared is proportional to the energy or intensity (I) of a sound.

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complex sound

A sound which has more than one (sine-wave) frequency component

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periodic sound

which repeats itself at regular intervals

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A sine wave is a _____ sound

simple periodic

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_______ produce complex periodic sounds.

They have a spectrum consisting of a series of _____.

Musical instruments or the voice produce complex periodic sounds.

They have a spectrum consisting of a series of harmonics.

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fundamental frequency

The lowest frequency (of which all the others a re multiples)

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harmonics

Each harmonic is a sine wave that has a frequency that is an integer multiple of the fundamental frequency.

Musical instruments or the voice produce complex periodic sounds. They have a spectrum consisting of a series of harmonics.

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Here is 1/20th of a second of the waveform and also the spectrum of a complex periodic sound consisting of the first 4 harmonics of a fundamental of 100 Hz.

All the frequency components are integer multiples of 100 Hz.

A periodic sound consists of a section of waveform that repeats itself.

The period of the complex wave is the duration of this section.
In this case, it is 1/100s or 0.01s, or 10 ms.

The period is the reciprocal of the fundamental frequency (in this case 100 Hz).
If you change the period of a complex sound, you change its pitch.

Shorter periods - higher fundamental frequency - higher pitch.

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If you change the period of a complex sound, you change its _____.

If you change the period of a complex sound, you change its pitch.

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Integer multiples of the fundamental frequency

Harmonics

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Spectrograms

A spectrogram is a 3-dimensional plot of frequency and amplitude as a function of time. Amplitude is represented in a spectrogram by shades of gray


Spectrograms are especially useful for representing complex waveforms like speech that change over time.

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Properties of Waves

Amplitude: Controlled by the magnitude of the forces that started the wave

Frequency: f of oscillations: controlled by forces starting the wave and by the nature of the material or object that is oscillating

Spectral Composition: Refers to the mixture of different frequencies in a wave

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Amplitude

Controlled by the magnitude of the forces that started the wave

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Frequency f of oscillations

controlled by forces starting the wave and by the nature of the material or object that is oscillating

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Loudness

most related to intensity

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Timbre

most related to spectral composition

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The 3 Main Perceptual Attributes of Sound

The terms pitch, loudness, and timbre refer not to the physical characteristics of sound, but to the mental experiences that occur in the minds of listeners.

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The 3 Main Perceptual Attributes of Sound

The terms pitch, loudness, and timbre refer not to the physical characteristics of sound, but to the mental experiences that occur in the minds of listeners.

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The 3 Main Perceptual Attributes of Light

The terms Brightness, Hue, and Saturation refer not to the physical characteristics of light, but to the mental experiences that occur in the minds of observers.

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Brightness

most related to amplitude

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Hue

most related to wave length or frequency

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Saturation

most related to spectral composition