WAVES

WAVESUnit 8, Lesson 8.1By Margielene Judan

Lesson OutlineIntroductionKinds of WavesCharacteristics of WavesSound WavesLight Waves

You may not have a scientific knowledge of waves, but you probably have a basic notion of what waves are based on what you see in everyday life.

Have you ever played this?

This is a slinky toy.

When you try to move in in a forward-backward or up-down motion, you produce a wave.

Also, suppose that you are the girl on the left. When the man (on the right) propagates the rope up and down, it creates a wave. The girl, being the receiver of the wave feels a force.

Take note that when the rope is moving, its particles are only moving in an up-down direction (see below). Each particle (dot) only moves in a two-way direction (up-down) not going to the girl.

Here, two cases are noted:The girls feels a force coming from the boy. The particle moves in an up-down direction, not towards the girl.

From that, we conclude thatA wave transfers energy, not mass.Indeed! You feel a force (it means energy is propagated/ transferred from the boy to you). Moreover, no particle is transferred to you (mass). If that happens, you would gain mass. Its absolutely absurd! You cannot get heavier by just propagating a rope!

This leads us to a formal definition of wave:

A wave is a simple disturbance through a medium in which energy is transferred.

In the case of our formal example, the rope is the medium to which energy is transferred.

Wave pulse simple disturbance (Figure a)Wave train series of disturbance (Figure b)Figure c is an endless sine wave.

Kinds of waves

KINDS OF WAVESAccording to the direction of movementTransverse WavesLongitudinal WavesAccording to their ability or inability to transmit energy through various media.Mechanical WavesElectromagnetic Waves

WAVES ACCORDING TO THE DIRECTION OF MOVEMENT

Transverse WavesMovement of particles = perpendicular to the direction that the wave moves

Transverse WavesConsider the rope wave earlier. The wave moves from left to right (large red arrow below), while the particles move up and down.

Transverse WavesThey form right angles, they are perpendicular.

left-right

up-down

Transverse WavesPerhaps, you think of waves only in terms of transverse waves, but there is another kind of wave.

Longitudinal WavesMovement of particles = parallel to the direction that the wave moves

Longitudinal WavesMovement of particles = parallel to the direction that the wave moves

WAVES ACCORDING TO THEIR ABILITY OR INABILITY TO TRANSMIT ENERGY THROUGH VARIOUS MEDIA

Mechanical WavesIncapable of transmitting energy through a vacuum (area without matter)Needs material such as solid, liquid, or gas to transmit energyMedium = matterEx. water waves, sound waves, earthquake waves

Mechanical WavesIt is mentioned that sound waves are mechanical waves. The reason behind why two astronauts cannot hear each other in space because sound waves cannot travel in a vacuum (space is a vacuum).Sound waves require matter to be transmitted. (ex. air)

Electromagnetic WavesCapable of transmitting energy through a vacuum Termed by physicist James Clerk MaxwellEx. Light, radio waves, microwaves, television waves

Electromagnetic WavesThats the reason why sunlight reaches the earth, because light doesnt need a material medium to transmit energy.

CHARACTERISTICS OF WAVES

CHARACTERISTICS OF WAVES

Transverse Waves (Crests and Troughs)Crest

CrestCrestTroughTrough

Transverse Waves (Amplitude half distance from crest to trough)Crest

CrestCrestTroughTroughAmplitudeAmplitudeAmplitude

Transverse Waves

AmplitudeAmplitudeAmplitude

Longitudinal Waves (Expansion and Compression)

Expansion*Amplitude is line density

Longitudinal Waves (Wavelength distance from compression to compression; expansion to expansion)

SOUND WAVES

SoundForm of energyProduced when air molecules vibrate and move in pattern known as waves or sound waves.

SoundIt is a longitudinal wave

To make vibrations become sounds, 3 basic elements must be present:Source produces wavesMedium vehicle to w/c sound travelsDetector or receiver

SourceMediumReceiver

https://www.youtube.com/watch?v=JStvGlpucVs

Since sound is a mechanical wave, it only travels through matter (solid, liquid, gas).Depending on the medium, sound waves travel at different velocities. In air, they travel at an average speed of 343 m/s at 20oC.

As seen, sounds travel fastest in solids, then liquids, the gases being the slowest. This is because molecules in a solid is more intact, thus, energy could be transferred easily.

Speed of sound Solid > Liquid > Gas

HOW HUMANS PRODUCE SOUNDS

The production of sounds is attributed to 3 parts:Lungs produce airflow and air pressureVocal folds within the larynx produces the sound by vibratingArticulators (tongue, palate, lips) articulate and filter the soundThey are all equally important

The vocal cord

The vocal cord (open and close position)

Length of vocal fold or cord:Men 17 mm to 25 mmWomen 12.5 mm to 17.5 mmThe larger the vocal cords, the lower the pitch of voice.

The higher the note, the tenser and more stretched the vocal cord.This would mean that we need to be more careful when we start to sing higher and higher notes, as our cord muscles are subject to more and more strain, and they would then be more vulnerable to vocal abuse.Various vocal warmup exercises to stretch out our vocal cords before singing to prevent unnecessary harm to our voice.

Why do we all have different quality of sounds?Different sizes and shapes of vocal cordsManner from w/c sound is articulated (trough the tongue, palate, lips)

https://www.youtube.com/watch?v=b89RSYCaUBo

DETECTING SOUNDS

Our ears detect sounds.

Transmission of sound:Outer ear acts as funnel to collect sound waves.Sound waves reaches the ear drum, causing it to vibrate.Vibrations are passed from the ear drum to the 3 bones (hammer, anvil, stirrup)The bones amplify the sound to the inner ear, which cochlea is found.Cochlea contains fluid that amplifies the vibration to the auditory nerve.Auditory never sends signals to the brain.

CHARACTERESTICS OF SOUND

Acoustics the science that focuses on the study of properties and transmission of sound

CHARACTERISTICS OF SOUNDTonePitchIntensity

Differences between sounds are caused by these 3.

CHARACTERISTICS OF SOUNDTone depends on the form of the wavePitch depends on the frequency of the waveIntensity depends on the amplitude of the wave

We will tackle this in more detail in the following slides.

ToneRefers to sound qualitydepends upon the form of the wavesMost sounds are not pure tones. Most are combinations of two or more tones (image below).

Wind TrioString QuartetOrchestraPianoThese are the sound waves produced by different instruments. Note that they all have the same pitch, but a different tone. (Press the play button to play.)

PitchRefers to subjective impression about the highness or lowness of a tonedepends upon the frequency of the wavesSound waves of the same frequency are of the same pitch.High frequency= high notesLow frequency = low notes

PitchThe human ear can hear sound of different frequencies. It usually varies with a person, usually with age. The audible range for humans is 20 to 20,000 Hz (hertz). Younger individuals tend to hear a wider range of frequencies waves. Some animals (dogs, bats, dolphins) can hear higher frequencies (above 20,000 Hz). They use it for sensing their environment and navigation.

PitchUltrasonic frequencies above 20,000 Hz Infrasonic frequencies below 20 Hz

NameFrequency RangeCharacteristicsInfrasonic0-20 HzEar cannot detect, but can be felt as vibrations.Sonic (or Audio)20 20,000 HzNormal range for human earsUltrasonic20,000 + HzHumans cannot detect, although some animals hear part ways into this range; also used in medicine

IntensityAmount of energy that is transported in a given area per unit time.depends upon the amplitude of the waves

IntensityRelated to loudness, but different in meaning.Intensity is the amount of sound energy in a waveLoudness is the sensation on the ear that the intensity producesHigh amplitude = louder sound

IntensityMeasured through the decibel system (dB).

Decibel system (dB)Works logarithmically, meaning:10 dB is 10x as intense as 0 dB.20 dB is 100x as intense as 0 dB.30 dB is 1,000x as intense as 0 dB.40 dB is 10,000x as intense as 0 dB.etcThe normal intensity is 71-90 dB, equivalent to regular daily sound like people talking.

Lets compare the effects of changing the amplitude and frequencies on the Minions Banana Song. (Click the play button). Notice the differences in the wave forms.

Normal Amplitude

Larger Amplitude

Smaller Amplitude

Lets compare the effects of changing the amplitude and frequencies on the Minions Banana Song. (Click the play button). Notice the differences in the wave forms.

Normal Frequency

Higher Frequency

Lower Frequency

Music and NoiseSome sounds are music to the ears, while others are considered noise.Noise is a more irregular sound wave.

LIGHT WAVES

In terms of the ability or inability of a wave to travel in a material medium (solid, liquid, gas), we have classified waves into:Mechanical waves needs material mediumElectromagnetic waves can travel in a vacuum

Sound is an important example of mechanical wave. Without a material medium (ex. air), we would not be able to hear each other.

Another important wave we will study in this chapter, is the light wave, which is an electromagnetic wave.

LightForm of electromagnetic waveResponsible for the sense of sightTravels a speed of 300,000,000 m/s, 3 X 108 m/s to be short.Exists as both a particle and a wave.

NATURE OF LIGHT

NATURE OF LIGHT(Pre-history)

PlatoThought that light is emitted by the eyeSupported by EuclidContradicted by the PythagoreansEmpedoclesForerunner of PlatoLight is composed of high speed waves

NATURE OF LIGHT(Development)

Two theories were developed on the basic nature of light:Wave Theory or Undulatory TheoryCorpuscular or Emission Theory

Wave TheoryLight is a wave.Light has a wave motion.It starts from a vibrating body (source) and is transmitted at high speeds.

James Clerk MaxwellEstablished the wave theoryHe constructed an oscillating electrical circuit which showed that changing electric and magnetic fields could produce electromagnetic radiation that could travel through a vacuum.

Heinrich HertzProved that light is electromagnetic. It could travel in a vacuum.Showed existence of another kind of electromagnetic wave, the radio wave.

Christian HuygensSupported the wave theoryLight can travel through a vacuum (without matter), which they called ether.

Sir Isaac NewtonContradicted the wave theoryProposed the Corpuscular or Emission Theory

Corpuscular or Emission TheoryLight is a stream of particles. It travels only in straight lines called rays, and not like waves.

Sir Isaac NewtonOne thing he observed is that light undergoes refraction (changes direction) upon hitting the water. He hypothesized that light must be an atom-like particle that changes its direction when it hits a medium with different density.

Sir Isaac NewtonHowever, long after his death in the 19th century, he was proved wrong by saying that light is like an atom particle. When two light rays/beams intersect, they do not change direction (refract).

Albert EinsteinObserved the photoelectric effect and supported the Emission Theory.Said that light is a stream of particles called photons, which are bundled in discrete quantities called quanta.

Corpuscular or Emission TheoryThe wave theory cannot explain a certain phenomenon, called the photoelectric effect. It can only be explained by the emission theory which supports that light must be a particle.

Photoelectric EffectEmission of electrons from a metal plate

Scientists were puzzled for hundreds of years regarding the true nature of light (particle or wave?)

NATURE OF LIGHT(Modern History)

Louis Victor de BroglieProposed that every particle of matter is somehow endowed with a wave to guide it as it travels.Hence, the particle-wave duality of light was born.

Particle-Wave Duality of LightSolved all the problems of whether light is a wave or a particle.Light acts as a wave and a particle.

ELECTROMAGNETIC SPECTRUM

Electromagnetic SpectrumA range of electromagnetic wavesArranged according to their frequency or wavelength.

Electromagnetic SpectrumThe colors we see (ROYGBV) is only part of the EM spectrum.Arranged from lowest to highest frequency (highest to lowest wavelength) is seen from left to right (see below)

Visible SpectrumRed has the longest wavelength (smallest frequency)Violet has the shortest wavelength (largest frequency)Indigo is not anymore distinguished as a separate color. Thus, we have ROY G BV rather than ROY G BIV.

Assignment (1 whole sheet of paper):Research and enumerate the uses of each electromagnetic wave: from radio waves up to gamma rays. Keep it short onlyEx. Infrared Infrared thermometersX-ray radiologic x-rayMicrowaves cooking Answer the Unit Test on page 288-289: Check Your Knowledge and Check Your Understanding.

LIGHT SOURCES AND PROPAGATION

Luminous objectsEmit or send off their own lightRadiate heat and store their own energyEx. sun, starts, fire, lasers, lamps, light bulbs

Nonluminous objectsCannot emit or send off their own lightThey only reflect light like the moon, which reflects light from the sun.Ex. moon, cars, buildings, people

PhotometryDeals with the measurement of visible lightBrightness is measured through luminous intensity expressed in candela (cd) units.

When light waves encounter any substance, they may either be:TransmittedRefracted ReflectedAbsorbed

TransmissionPasses through a substance or object

Refracted (refraction)Light changes direction upon passing through a different medium with different density (like passing a laser from air to water; it will change direction as seen below because water has different density than air)

Reflected (Reflection)Bounces back to the same angle

AbsorbedNot transmitted; absorbed rays are not seen anymore

Why are leaves green?-It reflects green light while it absorbs the rest of the colors (red, yellow, blue, violet). The color of the chlorophyll inside the chloroplast is green.

This applies to all colors seen.

Special colors that we perceive are:Black the absence of colorWhite the combination of all colorsIn black, all colors are absorbed, nothing is reflected.In white, all colors are reflected, nothing is absorbed.

Thats the reason why wearing dark colors during warm days is discouraged. In dark colors, more light waves are absorbed, meaning more heat is absorbed too.

Objects are classified in terms of the way they allow light to pass through:

TransparentAllow light to pass through clearly

OpaqueDoesnt allow passage of light; blocks light

TranslucentAllow only some amount of light to pass through, resulting in a blurred figure.Have both the characteristics of transparent and opaque objects

Laboratory 4.1 4.3 tomorrowEach group will be performing different experiments, as will be shown in the following slides.Each group must document their experiment. Bring a camera.Present the concept and the results on the next day by a powerpoint presentation. Show actual pictures. Be creativeThe day after the presentation, the leader will pass to me a written or type-written report about the contribution of each of his/her members. Each member will be rated from 1-10.The members will also rate their other groupmates, including the leader.

Laboratory 4.1 Group EvaluationCriteria:Content of Written Evaluation by the Leader 40%Evaluation from the Leader25%Evaluation from the Members25%Promptness in Submission10%(Youll get a perfect 10% if the leader passes the report on time during the next science class)Total100%

Laboratory 4.2Answer the answer sheet for your experiment. It will be graded accordingly.

Laboratory 4.3 Group PresentationCriteria:Content and Delivery30%Technicality (must be able to explain 30%well the scientific principles involved)Creativeness20%Documentation (must show actual pictures 10%of the performed experiment)Visual Aids (video, props, etc.)10%

Total100%