CONCEPTUAL PHYSICS: UNIT 4

Part 1: Properties of Waves SP4. Students will analyze the properties and applications of waves.

a. Explain the processes that results in the production and energy transfer of electromagnetic waves.

b. Experimentally determine the behavior of waves in various media in terms of reflection, refraction, and diffraction of

waves.

c. Explain the relationship between the phenomena of interference and the principle of superposition.

d. Demonstrate the transfer of energy through different mediums by mechanical waves.

e. Determine the location and nature of images formed by the reflection or refraction of light.

A vibration is a repetitive back-and-forth motion around a fixed position. Vibration is one form of kinetic energy.

Vibrations are transferred through matter by pulses of energy or by waves. A pulse is a single disturbance or ripple that

moves outward from the point of disturbance. Waves can move as a single pulse or as a continuous series, carrying energy

away from its source.

A wave is a traveling disturbance that carries energy from one location to another. Waves carry energy away from the source

of the disturbance, waves spread the energy outward away from the source of the disturbance. There are two classes of

waves: Mechanical Waves and Electromagnetic Waves. Electromagnetic waves are the waves that form when light is

emitted from a source. Electromagnetic waves will be discussed later.

Mechanical waves are waves that must pass through matter. Mechanical waves propagate, or travel, through solids, fluids,

or gases. Mechanical waves cannot move through a vacuum, such as in space. As a mechanical wave passes through matter,

the matter is temporarily deformed by the wave energy. There are two types of mechanical waves: Longitudinal Waves and

Transverse Waves. A standing wave is a special type of mechanical wave.

A longitudinal wave is a compression wave. As the wave moves through the medium, the molecules in the medium are

temporarily compressed and expanded by the wave—molecules are bunched up then pulled apart. The direction of the

wave’s energy is in the same direction as the wave moves. The regions of the medium where molecules are temporarily

compressed are called compressions or condensations. The regions of the medium where molecules are temporarily

expanded are called rarefactions. Sound waves are examples of longitudinal waves. Sound travels through air (gas), water

(liquid), and walls (solids), but sound cannot travel through space because space is a vacuum.

A transverse wave is a sinusoidal wave. Transverse mechanical waves cause the molecules in the medium to move up-and-

down as the wave passes. The direction of the wave’s energy is perpendicular to the direction as the wave moves. The

regions of the transverse wave where the molecules are pushed up relative to the equilibrium position are called crests. The

regions of the transverse wave where the molecules are pushed down relative to the equilibrium position are called troughs.

Transverse waves are mechanical waves, and also must pass through a medium. They cannot pass through a vacuum.

A standing wave is a vibration that is produced by a taut string or wire that vibrates back and forth with a high frequency.

Standing waves produce the sound in stringed instruments and pianos.

Longitudinal Wave

Transverse Wave

Standing Wave

All mechanical waves produce work. As the wave passes through the matter, the energy of the wave causes matter to move.

Thus longitudinal waves, transverse waves, and standing waves perform work—work against resistance and mechanical work

by pushing and pulling the molecules in the medium through which they pass.

Frequency and Period

An oscillation or vibration is a repetitive back-and-forth motion. One cycle is defined as one complete back-and-forth

motion of a vibration or of a wave. The time it takes to complete one cycle (one wave or one vibration) is called the period.

The frequency of a wave is defined as the number of waves, cycles, or vibrations per second. Frequency is reported in units

of Hertz, abbreviated Hz. A Hertz is a number per second, (units of s in the denominator). Period is calculated as the

reciprocal of frequency. Period is reported in units of seconds.

Frequency: t

wavesf

# or

t

cyclesf

# or

t

vibrationsf

#

Period: f

T1

The relationship between frequency and period:

The greater the frequency (more waves, vibrations, or cycles per second), the shorter the period.

The lower the frequency (less waves, vibrations, or cycles per second), the longer the period.

The relationship between frequency and the energy of the wave or vibration

The greater the frequency, the greater the energy (more kinetic energy and more heat)

The lower the frequency, the lower the energy (lesser kinetic energy and lesser heat)

Amplitude and Equilibrium Position

Amplitude is the maximum displacement of the wave from its equilibrium position. The equilibrium position is the “rest”

position of the molecules if the wave was not passing through the medium. The equilibrium position is the mid-point

position around which the vibration or wave moves.

For example, the dashed line of the standing wave represents the equilibrium position of the plucked string. The string

vibrates up-and-down around the equilibrium position. The amplitude of the standing wave is the maximum displacement in

the up direction or down direction of the string from the equilibrium position. For the transverse wave, the equilibrium

position is the imaginary line around which the wave oscillates. The amplitude is the maximum displacement in the up (crest)

or down (trough) direction of the wave.

The relationship between amplitude and the energy of the wave or vibration

The greater the amplitude, the more work was done to move the medium molecules in the up-and-down direction, the

greater the energy (more kinetic energy and more heat).

The lesser the amplitude, the lesser work was done to move the medium molecules in the up-and-down direction, the lesser

the energy (less kinetic energy and less heat).

amplitude

f = frequency (Hz)

t = time (s)

T = Period (s)

Frequency and Wavelength

The relationship between frequency and wavelength is determined by the following series of equations that have been

algebraically rearranged. The product of the frequency of the wave and the wavelength of the wave is always the wave speed.

fc

cf

f

c

Wave Speed

Wave speed is the speed of the wave moving through a given medium. Treat wave speed like a normal speed—the wave

moves a given distance per unit time. Wave speeds may be reported in units of m/s, km/hr, or km/s depending on the context

of the wave.

Wave speed is denoted by the letter c. This applies to the speed of sound, speed of light, or speed of seismic waves.

Wave speed: t

dc

Wave speed is dependent on many factors, such as temperature and the medium through which the wave is moving.

Practice Problems for Review

A guitar string vibrates at a rate of 42000 oscillations per minute. The speed of sound in air at 20ºC is 343 m/s.

Calculate the frequency (f) of the guitar string in Hz.

Calculate the period (T) of the vibration. (s)

Calculate the wavelength (λ) of the vibration. (m)

A horn emits a sound with a frequency of 6500 Hz. The speed of sound in air at 20ºC is 343 m/s.

Calculate the period (T) of the sound waves emitted from the horn. (s)

Calculate the wavelength (λ) of the sound waves. (m)

Wavelength is defined as the distance between two identical positions

on two adjacent or consecutive waves. Wavelength could be crest-to-

crest, trough-to-trough, or node-to-node. In the diagrams, the

wavelength is shown as crest-to-crest.

Wavelength is a distance, and is reported in units of meters. The

diagram to the left shows two different waves. The top wave is a

“high frequency” wave. The bottom wave is a “low frequency” wave.

The top wave has more cycles per unit time whereas the bottom wave

has fewer cycles per unit time.

There is an inverse relationship between frequency and wavelength.

If a wave has a high frequency, the wavelength of the waves is

shorter.

If a wave has a low frequency, the wavelength of the waves is

longer.

f = frequency (Hz)

c = wave speed (m/s)

λ = wavelength (m)

c = wave speed (m/s)

Δd = distance traveled (m)

t = time (s)

A pendulum completes 10 back-and-forth swings in 35 seconds.

Calculate the frequency of the pendulum in Hz.

Calculate the period of the pendulum’s motion.

A spring oscillates with a frequency of 2.5 Hz.

Calculate the period of the spring’s oscillation.

Calculate how many back-and-forth cycles the pendulum will make in 1 minute.

A whale’s song has a frequency of 400 Hz. The speed of sound passing through seawater at 10ºC is 1530 m/s.

Calculate the period of the sound waves of the whale’s song.

Calculate the wavelength of the sound waves of the whale’s song.

The siren on the top of an ambulance produces a sound with a frequency of 12,000 Hz. The speed of sound in air at 20ºC is

343 m/s.

Calculate the period of the sound waves of the siren.

Calculate the wavelength of the sound waves of the siren.

An earthquake occurs. The seismic waves (earthquake shaking waves) travel through the crust at a speed of 5900 m/s (5.9

km/s). The frequency of the earthquake waves is 250 Hz.

Calculate the wavelength of the earthquake waves.

Calculate the distance that the earthquake waves traveled after

2 seconds

4 seconds

10 seconds

30 seconds

1 minute

CONCEPTUAL PHYSICS: UNIT 4

Part 2: Properties of Electromagnetic Radiation

SP4. Students will analyze the properties and applications of waves.

a. Explain the processes that results in the production and energy transfer of electromagnetic waves.

b. Experimentally determine the behavior of waves in various media in terms of reflection, refraction,

and diffraction of waves.

e. Determine the location and nature of images formed by the reflection or refraction of light.

What Is Light Made Of?

Electromagnetic radiation (EMR) is the technical term for light. Light is radiant energy. Light, or EMR travels through

space and through transparent media as an electromagnetic wave. Electromagnetic waves have three components: the photon,

the traveling electric field, and the traveling magnetic field. Unlike mechanical waves, EMR can travel through a vacuum

like space. It will also travel through any medium that has a high degree of transmission.

A photon is a compact packet of energy. The photon behaves like a particle because energy is so concentrated into a very

tiny space, but the photon has no mass. Photons give light its energy. When matter generates light, the matter releases the

photon. As the photon moves through space or air, the photon’s motion and interaction with molecules that it passes creates

the electric field and the magnetic field. The electric field and magnetic field are invisible perpendicular forces. They are

always present and accompany the moving photon.

Classes of Electromagnetic Radiation

There are seven classes of electromagnetic radiation (EMR). Electromagnetic radiation means light, thus there are seven

classes of light.

Gamma rays have the most energy, the shortest

wavelength, and the greatest frequency. Radiowaves

have the lowest energy, the longest wavelength, and the

lowest frequency. Visible light is the only class of light

that can be detected by the human eye. The other

classes of EMR are invisible to the human eye.

Gamma rays, x-rays, and ultraviolet radiation are called

ionizing radiation because they have enough energy to

break chemical bonds in molecules. That makes them

dangerous because gamma, xray, and ultraviolet light

can damage soft body tissues and DNA.

Infrared, microwave, and radiowaves tend not to be not

harmful because they have very low energy.

Visible Spectrum

The visible spectrum, sometimes called the color spectrum, is composed of the wavelengths of visible light. Human eyes can

only detect visible light. Human eyes cannot detect the other forms of EMR—they appear invisible to human eyes.

White light is the total collect of all wavelengths of

color light in the visible spectrum. If rays of white

light are passed through a glass prism, the double

refraction of the light will separate the white light into

the different wavelengths of color: ROYGBIV

Violet is the most energetic of the visible light, with

the shortest wavelength, and the greatest frequency.

Conversely, red is the least energetic of the visible

light, with the longest wavelength, and the lowest

frequency.

The Color of Objects

White light is the total collection of all visible light wavelengths in the visible spectrum. All colors are present in white light:

ROYGBIV. The color of objects, or hue, is determined by which wavelengths of the color spectrum are absorbed by matter

and which wavelengths are reflected by matter. Absorbance is where matter captures and assimilates energy—energy is

absorbed and converted to heat. Reflection is where waves (light, sound, mechanical waves) bounce off of a surface without

changing frequency.

If you see a blue color of an object, like a blue shirt or a blue car that means that the object is reflecting the blue

wavelengths of the visible spectrum (B) and absorbing the other colors (ROYG, IV).

If you see a red color of an object, like a red flower or a red fire truck, that means that the object is reflecting the red

wavelengths of the visible spectrum (R) and absorbing the other colors (OYGBIV).

The color black is observed when there is an absence of color or visible light. Black may be the result of 100% absorbance

of all visible light by matter, all light is absorbed and none is reflected to the eye. The dark blackness of space beyond

starlight is observed because there is no visible light in interstellar space. There is, however, light in the blackness of

interstellar space in the form of microwave radiation (microwaves) which cannot be seen with the unaided eye.

Emission of Light

Objects that generate and emit their own light are described as luminous

or having luminosity. The release of EMR by matter is called emission.

Light is emitted by atoms when very energetic or excited electrons (the

negatively-charged subatomic particles that flow around the nuclei of

atoms) “relax” or return to their normal state as they were before they

were excited. One photon is given off each time an electron relaxes,

forming an EMR wave that is emitted by the atom. All matter releases at

least one form light. The emission of light is dependent on how the

electrons got excited and by the temperature and the type of matter that is

emitting the light.

Another way that that light can be emitted is through radioactive decay.

When certain unstable nuclei of atoms disintegrate (change the number of

protons or neutrons in the nucleus), x-rays or gamma rays are emitted.

The electrons are excited by energy (heat, other light, kinetic

energy, electricity). When the excited electrons return to

their normal state, they release energy as a photon—a wave of light is given off.

Very cold interstellar space, temperatures 2-3 Kelvin, contains microwave background radiation.

Objects with temperatures between 3-2500 Kelvin radiate the majority of their heat in the form of infrared.

Hotter objects 2500-20,000 K radiate visible light and some and ultraviolet light.

Radioactive materials radiate x-rays and gamma rays as their nuclei disintegrate.

CONCEPTUAL PHYSICS: UNIT 4

Part 3: Interactions of Waves and Light with Matter

SP4. Students will analyze the properties and applications of waves.

a. Explain the processes that results in the production and energy transfer of electromagnetic waves.

b. Experimentally determine the behavior of waves in various media in terms of reflection, refraction,

and diffraction of waves.

e. Determine the location and nature of images formed by the reflection or refraction of light.

Speed of Light

The speed of light (or light speed) in a vacuum such as space is 300,000,000 m/s (three hundred million meters per second).

In one second time, light will travel 300,000,000 meters. The speed of light is the greatest physical quantity in the universe

and represents the uppermost limit of motion. No object or other energy can travel faster than the speed of light. In contrast,

the speed of sound in air at 20ºC is 343 m/s. The speed of light is 874,635 times greater than the speed of sound.

Additionally, the speed of light applies to ALL CLASSES OF EMR. Every type of EMR travels at the speed of light

regardless of their differences in frequency and wavelength: gamma rays travel at 300,000,000 m/s and radio waves travel at

300,000,000 m/s.

A light year is the distance that light travels in one calendar year. In 1 second, light travels 300,000,000 m. In 1 calendar

year, light travels 9.47x1015

m. (9,470,000,000,000,000 m). Light years are used to quantify very, very large distances

between stars and between galaxies. For example, the closest star to our Sun is called Proxima Centauri (“Near Centaur”).

Proxima Centauri lies 4.4 light years away. Starlight emitted by Proxima Centauri will take 4.4 years to reach our solar

system.

As light passes through different materials, the speed of light will be different. As a

general rule, the speed of light decreases as the density of the material through which it

passes increases—the greater the density, the lower the speed of light through that

material. The speed of light through a vacuum (empty space) is 1.5 times greater than the

speed of light through glass.

Speed of Light

Vacuum: 300,000,000 m/s

Air: 299,000,000 m/s

Water: 256,000,000 m/s

Glass: 200,000,000 m/s

Transmission of Light If a medium has a high degree of transmission, light will pass through that medium with little interference, scattering, or

diffusion. Air, glass, and still water are transparent media. A transparent medium will allow light to pass through it.

Images can be clearly seen through transparent media. Translucent media will allow light to pass through the surface into

the medium’s interior, however, the medium will distort or blur the light. Clear images cannot be seen on the other side of

translucent media. Examples of objects that are translucent include milk and gemstones. An opaque medium will not allow

light to pass through it. Light is either absorbed or reflected away from the surface, no light will penetrate into the medium’s

interior. If light shines on an opaque object, a shadow will be projected on surfaces opposite the light source.

Absorbance of Light

Absorbance is the assimilation of EMR by matter. Absorbance occurs when the photons in EMR waves (the compact

packets of energy) are taken in by the molecules in matter upon which they impact. That light energy adds kinetic energy to

the molecules, which causes the temperature of the matter absorbing the light to increase (get hotter). If you stand outside on

a hot summer day in direct sunlight, sunlight striking your skin will cause your skin to feel warmer—EMR energy is

converted to KE in the molecules in your skin which causes the increase in temperature. Dark colored objects have the

greatest absorbance. Asphalt, soil, and dark-colored clothing will absorb the majority of visible light rays that strike their

surfaces and reflect very little light. That is why asphalt and soil gets hot very fast in direct sunlight. In contrast, light

colored objects with smoother surfaces will reflect more light and absorb very little light. Clouds, ice, snow, and light-

colored clothing reflect the majority visible light that strikes their surfaces.

Reflection of Light Reflection is the redirection of waves (light, sound, or mechanical) by a surface or boundary. The frequency and wavelength

of the waves do not change when they are reflected, only the direction changes. There are two types of reflection: Perfect

reflection and diffuse reflection. Perfect reflection (left diagram) is where incoming light strikes a smooth reflective surface

and the rays of light are reflected away in parallel. Mirrors and polished metals will create perfect reflection. Diffuse

reflection (right diagram) occurs when incoming light strikes an irregular surface and the rays of light are reflected away in

multiple directions. All non-polished, irregularly shaped objects will produce diffuse reflection.

When perfect reflection occurs, the rays of light obey the

Law of Reflectance. The Law of Reflectance states: the

angle of incidence equals the angle of reflection. In other

words, the angle of the incoming light before it strikes the

reflective surface must equal the angle of the light leaving or

reflected from the reflective surface. The incident and

reflected angles are measured relative to the normal ray.

Refraction

Refraction is the bending or change of direction of

waves (light, sound, or other mechanical waves) as

the wave passes through a boundary between two

media with different densities. Refraction is

always accompanied by the change in direction of

the wave and the change in speed. Consider the

two scenarios with light passing between air and

water.

Left: Light from air passes through the boundary

into water. The light slows because water is

denser than air and is refracted toward the normal.

Right: Light from water passes through the

boundary into air. The light speeds up because air

is less dense than water and is refracted away from

the normal.

Lenses

Double Convex Lens (converging)

A lens is curved, polished glass that uses refraction to transmit or

focus the light rays passing through it. Converging lenses focus

(bring together) light rays to a common point where all of the light

rays cross. Diverging lenses cause light rays to spread out or

diverge.

A double convex lens is an example of a converging lens.

Converging lenses bring light together, intensifying the incoming

light rays. Their images appear larger and clearer. Notice that as the

parallel rays of light pass through the lens, the rays are refracted

toward each other and eventually cross at the same point beyond the

lens, called the focal point. The lenses in magnifying glasses,

microscopes, and refracting telescopes are converging lenses.

A double concave lens is an example of a diverging lens. Notice

that as the parallel rays of light pass through the lens, the rays

diverge or spread out away from each other. Diverging lenses

increase the size of real images that are projected onto surfaces. The

lenses in projectors are diverging lenses.

Converging and diverging lenses have focal points and focal lengths. The focal point or focus is the locus where light rays

converge or cross each other. The focal length is the distance between the geometric center of the lens and the focal point.

For the double convex lens, light converges at the focal point on the side of the lens opposite the light source. Real images

viewed at the focal point are enlarged and clear. Images viewed at a distance less than the focal length are blurry but right-

side up. Images viewed at a distance greater than the focal length are blurry and upside-down. For the double concave lens,

the focal point is imaginary and located on the same side as the light source.

Diffraction

Diffraction is the bending of waves (light, sound, mechanical waves) around obstacles and the spreading out of waves (light,

sound, mechanical) that pass through small openings. Diffraction

On the next page, the left diagram shows waves being intercepted by a boundary (wall) with a small opening. Most of the

wave is absorbed by the boundary, a small fraction of the wave passes through the opening. Once the portion of the wave

passes through the opening, the wave begins to spread out. The farther way travels beyond the opening, the greater the wave

will spread out.

Double Concave Lens (diverging)

The right diagram shows waves being intercepted by an obstacle. The obstacle absorbs the portion of wave that contacts the

obstacle. The remainder of the wave passes unobstructed on either side of the obstacle. Once past the obstacle, the waves on

either side of the obstacle spread out. Immediately behind the obstacle is a wave shadow.

Luminosity and Brightness

Objects that generate their own light are characterized as being luminous. Most luminous objects produce light by

incandescence. Incandescence is the emission of visible light by matter when matter is heated to very hot temperatures.

Incandescent light bulbs emit white light when the tungsten filament is heated to > 2000ºC. The very hot gases in fire glow

by incandescence. Visible starlight is the result of incandescence because the surfaces of stars are very hot.

Luminosity is the power of light energy released by a light emitting source. Luminosity, or light power, is measured in the

units of Watts. For example, the power rating of light bulbs is reported in Watts (Joule/s). A 100 Watt light bulb releases

100 Joules of radiant energy per second. In other words, in 1 second, a 100 Watt light bulb releases 100 Joules of energy.

The greater the luminosity, the more light waves and more photons are released by the light emitting source. The lower the

luminosity, the lesser the light waves and fewer photons are released by the light emitting source. Brightness, or the

intensity of light as seen by an observer, is controlled by three factors: (1) the luminosity of the light source, and (2) the

distance between the light source and the observer, and (3) the amount of light scattering or interference between the source

and the observer.

Scattering is the random redirection or reflection of light rays as light passes through air. The oxygen and nitrogen gas

molecules in the atmosphere scatter some of the violet, indigo, and blue wavelengths of the visible spectrum. This is why the

daytime sky is bluish white in color. Very tiny suspended dust and ash particles, pollution aerosols (smog), and cloud

droplets scatter light as well. On clear days, visibility is much greater. On days with haze, smog, or cloudy conditions,

visibility is limited because most of the light passing through those clouds or smog zones is scattered and little light is

diffused to the eye.

Luminosity

The greater the luminosity of the source, the more light rays and photons released by the source, the brighter

the light will appear.

The lesser the luminosity of the source, the fewer light rays and photons released by the sources, the dimmer

the light will appear.

Distance

The closer the observer is to the light source, a greater percentage of light rays are directed to the eye, the

brighter the light will appear.

The farther away the observer is to the light source, the lower percentage of light rays are directed to the

eye, the dimmer the light will appear.

Scattering

The lesser the scattering, the fewer light rays are randomly reflected by suspended dust, particles, and gas

molecules in the atmosphere, the brighter the light will appear.

The greater the scattering, the more light rays are randomly reflected by suspended dust, particles, and gas

molecules in the atmosphere, the dimmer the light will appear.

CONCEPTUAL PHYSICS: UNIT 4

Part 4: Sound and Sound Waves

Sound Waves

Sound is energy that moves as a traveling vibration

in the form of longitudinal waves. Like all

mechanical waves, sound waves propagate or

travel through matter—solids, fluids, and gases—

but cannot travel through a vacuum like space. The

compressions of the sound wave are called wave

fronts. Wave fronts are traveling pulses of higher

pressure created when air molecules are bunched up

Wave fronts carry the energy of the sound wave.

When the wave fronts impact the ear or sound

detector, they carry the intensity of the sound, the

sound is loud. The greater the number of molecules

bunched up at the wave front, the thicker the wave

front, the greater the pressure, the louder the sound

will be perceived. Conversely, the rarefactions or the regions between wave fronts where air molecules are spread out or

expanded, carries little intensity of the sound, the sound is very soft or no sound. The sinusoidal wave below the longitudinal

wave in the diagram above is to provide reference. The crests represent the wave fronts or regions of higher pressure—loud

sound. The troughs represent rarefactions or regions of lower pressure—soft sound.

Speed of Sound

The speed of sound is much lower than the speed of light. This can be observed during a thunderstorm. One always sees a

lighting strike before hearing the thunder. Light travels through air at 299,000,000 m/s. In contrast, at 20ºC, sound travels

through air at 343 m/s. Light travels ~872,000 times faster than sound. The two greatest factors affecting the speed of sound

is density and temperature of the medium through which sound travels.

Sound travels faster through denser materials. Sound travels

slower through lesser dense materials. This is true because

sound travels as a longitudinal wave, a moving vibration. If

molecules are closer together and packed in a tight

configuration, the vibration and wave fronts can easily move

from molecule to the next molecule, bunching them up

easily. Sound travels fastest through dense solids. Sound

travels slowest through gases.

Speed of Sound

Air 20ºC: 343 m/s

Ethanol 25ºC: 1270 m/s

Water 25ºC: 1500 m/s

Lead: 2160 m/s

Glass: 5100 m/s

Steel: 5900 m/s

Speed of Sound in Air

Air 0ºC: 331 m/s

Air 10ºC: 337 m/s

Air 20ºC: 343 m/s

Air 30ºC: 349 m/s

Air 40ºC: 355 m/s

Sound travels faster through hotter materials. Sound travels slower through cooler materials. This is true because sound

waves are traveling vibrations in a longitudinal wave. They are kinetic energy. If the material is hotter, the kinetic energy in

the matter is greater. Thus, as the wave passes through the material with the greater kinetic energy, the vibrations are passed

through faster. If the wave passes through cooler materials with lesser kinetic energy, the vibrations are passed through

slower.

The speed of sound, c, is equal to the distance that sound travels divided by the time of travel: t

dc

.

Objects that move at subsonic speeds are moving slower than the speed of sound. Objects that move at transonic speeds are

moving at the speed of sound. Objects that move at supersonic speeds are moving at speeds greater than the speed of sound.

When objects “break the sound barrier”, the wave fronts or compressions of the sound generated by the supersonic object

collect and become thicker and more intense, called a shockwave. When the shockwave passes by, a thunderous violent roar

is created called the sonic boom.

c = wave speed (m/s)

Δd = distance traveled (m)

t = time (s)

Frequency and Wavelength of Sound

Frequency is the number of vibrations, waves, or cycles passing a given position per second. Wavelength is the distance

between two identical positions on two consecutive waves. Remember, frequency is inversely proportional to wavelength.:

The higher the frequency, the shorter the wavelength; the lower the frequency, the longer the wavelength. The frequency of

sound affects pitch. Pitch is the quality of sound received by and interpreted by the human ear. If sound has lower frequency,

the ear detects sound that is bass (low). If sound has a higher frequency, the sound is more shrill (high). A tuba produces

low frequency sound (200-300 Hz) which has a more bass pitch. A trumpet produces a medium frequency sound (600-900

Hz). A flute produces a high frequency sound that has a more shrill pitch (1000-3000 Hz). The sounds emitted by pianos

encompass a very large range of frequency (30-4000 Hz).

The audible range of typical human hearing is 20 Hz to 20,000 Hz. Most human ears can detect sound with frequencies in

that range. Humans cannot hear or detect sound outside of that range. Most mammals can hear higher frequency sound.

Infrasonic waves are sound waves that have frequencies below 20 Hz. Ultrasonic waves are sounds that have frequencies

greater than 20,000 Hz. Some seismic waves, whale songs, and thunder are infrasonic. Bats and dolphins emit ultrasonic

pulses for echolocation.

The relationship between frequency and wavelength of sound is determined by the following series of equations that have

been algebraically rearranged. The product of the frequency of the wave and the wavelength of the wave is always the speed

of sound (wave speed).

fc

cf

f

c

Reflection and Refraction of Sound

An echo is the reflection of sound waves off of a solid

surface or boundary. Sound is emitted by the sound

producing source, soundwaves strike the surface or

boundary, and are reflected back to the source. For a

true echo, the sender/receiver must hear distinctly the

sound when it was originally emitted and the reflected

sound. The emitted sound and reflected sound should

not overlap.

A reverberation is when the reflected sound waves

overlap with emitted sound waves. There is not enough

time between when the original sound wave emitted by

the source and the reflected sound returns. The original

sound and reflected sound cannot be distinctly heard.

Sound waves (like all waves) will refract.

Refraction is the bending of waves as waves pass through a boundary from one medium into another. Remember, wave speed also

changes. In the diagram to the upper left, sound waves are being refracted as sound passes through air of different temperatures.

When the wave fronts encounter warmer air, sound waves speed up and bend away from the ground. When the wave fronts

encounter cooler air, sound waves slow and bend toward the ground. In the diagram to the upper right, sound waves cross the

boundary from air into water. Notice that the sound waves speed up and change direction as they pass into the water because water

is denser than air.

f = frequency (Hz)

c = wave speed (m/s)

λ = wavelength (m)

Resonance

Resonance is the ability of objects to vibrate or oscillate

when waves of selective frequencies pass through them. For

the object to vibrate or sway or oscillate, the object must

have a fundamental frequency (the frequency that it will

cause it to vibrate) that matches or is an integer value of the

frequency of the wave passing through it.

Resonance occurs when there is a forced transfer of waves or

vibrations from a source (an object that is emitting vibrations

or sound) and another object. For example, if you strike a

tuning fork, the prongs begin to vibrate and emit sound

waves. The air transfers the sound waves to the adjacent

tuning fork. The frequency of the impacting wave fronts

causes the second tuning fork to vibrate. The second tuning

fork had a fundamental frequency that was the same, or an integer value of the first tuning fork, otherwise the second turning

fork would not have vibrated.

Another example of resonance is during earthquakes. Seismic waves passing through the crust will be transferred upward

from the crust into the foundations of buildings. Very tall buildings, like skyscrapers, may sway during earthquakes, not

because of the shaking at the ground, but because of the resonance of the seismic waves transferring wave energy upward to

the structure. If the structure has the same fundamental frequency as the seismic wave, the structure will sway with a

frequency equal to the frequency of the seismic wave.

Volume and Sound Intensity

Volume is the loudness of sound. Intensity is the power of sound energy at a given distance away from the sound emitting

sources. The two are related. Volume is a function of the amplitude of the sound wave. The greater the air is compressed at

the wave front, the more molecules bunched up in the condensation, the louder the volume will be. The intensity of sound is

greatest at the sound emitting source. As sound waves move away from the source, the sound waves spread out into thinner

and thinner wave fronts. Because of the thinning out of the waves as they move away from the source, the volume and

intensity of the sound decreases. A person standing 1 meter in front of a music speaker will hear more intense sound and

louder volume than a person standing 10 meters away, who will hear more intense sound and louder volume than a person

standing 50 meters away.

Sound intensity is measured in decibels (ten-bels). Decibels is a base-10 logarithmic scale of measure that characterizes the

intensity of sound.

The table below shows typical intensity of sound in decibels for everyday objects.

Decibel Loudness Object

0 Threshold of hearing

10 Very faint Watch ticking

20 Very faint Whisper

30 Faint Quiet conversation

40 Faint Tapping foot

50 Moderate Normal Conversation

60 Moderate Normal car engine

70 Loud Rock music on radio

80 Loud Alarm clock

90 Very loud Machines in factory

100 Very loud Lawn mower

110 Deafening Train locomotive

120 Deafening Plane taking off

Name: ______________________________________ Block: ____________

Partners: ___________________________________________________________________________

ACTIVITY 1: OSCILLATING SPRINGS

There are four springs attached to spindles, labeled Spring 1, Spring 2, Spring 3, and Spring 4. The springs are identical but

have different masses attached to the bottoms. The springs initially hang at rest. Gently lift the bottom of the spring 4-5

inches higher than the rest position, then allow the spring to fall. The spring should obtain a perpetuating uniform up-and-

down motion. Using the stopwatch, measure the amount of time it takes to for the spring to oscillate 10 consecutive times.

Record this value in the table below. Repeat this procedure 4 times and record your time data. Calculate the average time for

each spring to oscillate 10 times. (Average = sum the times, divide by 4).

Trial 1 Trial 2 Trial 3 Trial 4 Average Time

(seconds)

Spring #1 Spring #2 Spring #3 Spring #4

Calculate the frequency and the period of each spring. Use the average time (seconds)

Frequency: t

sOssilationf

# Period:

fT

1

Frequncy (Hz) Period (s)

Spring #1 Spring #2 Spring #3 Spring #4

ACTIVITY 2: SWINGING PENDULUMS

There are five pendulums (bobs on the end of strings): Pendulum 1, Pendulum 2, Pendulum 3, Pendulum 4, and Pendulum 5.

The pendulums initially hang at rest. Use the meter stick to measure the length of the pendulum from the center of the bob to

the wooden support. Record this value in cm in your calculations table. Gently lift the bob (ball at the end of the string)

upward with the string tight and release to induce a low angle back-and-forth swing. Do not push the bob, allow gravity to

move the bob. The bob should have a uniform back-and-forth swinging motion. Using the stopwatch, measure the amount

of time it takes for the pendulum to swing back-and-forth 10 consecutive times. Record this value in the table below. Repeat

this procedure 4 times and record your time data. Calculate the average time for each pendulum to swing back-and-forth 10

times. (Average = sum the times, divide by 4).

Trial 1 Trial 2 Trial 3 Trial 4 Average Time

(seconds)

Pendulum #1 Pendulum #2 Pendulum #3 Pendulum #4 Pendulum #5

Calculate the frequency and the period of each spring. Use the average time (seconds)

Frequency: t

nsOscillatiof

# Period:

fT

1

Length of

pendulum (cm)

Frequncy

(Hz) Period (s)

Pendulum #1 Pendulum #2 Pendulum #3 Pendulum #4 Pendulum #5

On a separate piece of paper, NEATLY write 1 paragraph that analyzes your observations with the

springs and with the pendulum. You should discuss the differences with the springs because of the

additional masses added to the springs. You should discuss the differences with the pendulums because

of the different lengths of string from which they swing. Give reasons for why you think the springs and

the pendulums behaved that way.

Your paragraph should be original and not shared with your partners.

Name: ___________________________________ Block ________

Must be submitted by Tuesday, November 12, 2013.

Conceptual Physics: Unit 4

Properties of Waves and Sound

A. In the diagram below, identify the parts of a transverse wave by using the provided definitions.

_______ = crest The highest point of the wave above the line of origin.

_______ = trough The lowest point of the wave below the line of origin.

_______ = equilibrium position Signifies the original position of the medium.

_______ = wavelength The distance between two consecutive crests.

_______ = amplitude The distance from the equilibrium position to a crest or

trough of a wave.

B. Look at the transverse wave diagrams 1-6. Identify which wave is described by the questions.

Which wave has the greatest frequency?

Which wave has the lowest frequency?

Which wave has the greatest wavelength?

Which wave has the shortest wavelength?

Which wave has the greatest amplitude?

Which wave has the lowest amplitude?

Which two waves have the same frequency?

Wave #1 Wave #2

-2.4

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

-2.4

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Wave #3 Wave #4

-2.4

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

-2.4

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Wave #5 Wave #6

-2.4

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

-2.4

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Sound Cloze

Fill in the blanks with words from the box. compression echo echolocation energy

flat frequency medium pitch rarefaction vacuum vibrates wave

The string vibrations produce

sound that travels through the

air to your ears.

Sound is a form of _________________ that people can hear.

Sound is produced when an object _________________ back

and forth. When an object vibrates, it pushes the air around it, which

causes the air to alternately bunch up and then spread apart. When

the air particles bunch up, it’s called a _________________ and

when the particles spread apart, it’s called a

_________________. These compressions and rarefactions

travel outwards forming a sound _________________. The

material that the sound wave moves through is called a

_________________. Without a medium, sound cannot travel

and so there is no sound in a _________________ such as outer

space. The _________________ of a sound wave is a measure of

how many times an object vibrates per second. Objects that vibrate

with a high frequency produce sounds with a high

_________________, which is how our ears perceive sound. Sometimes sound waves bounce off

a hard, _________________ surface producing an _________________. Some animals such

as bats and whales use echoes to locate prey. Using echoes to locate an object is called

_________________.

Conceptual Physics: Unit 4

Homework: Properties of Waves

Name: ______________________________________ Block: ____________

Due Wednesday, November 13

t

Wavesf

#

fT

1

Tf

1 fc

f

c

t

dc

f = frequency (Hz)

t = time (s)

T = period (s)

λ = wavelength (m)

c = wave speed (m/s)

d = distance (m)

Problem 1: A whale’s song has a frequency of 400 Hz. The speed of sound passing through seawater

at 10ºC is 1530 m/s.

A. Calculate the period of the sound waves of the whale’s song.

B. Calculate the wavelength of the sound waves of the whale’s song.

Problem 2: The siren on the top of an ambulance produces a sound with a frequency of 12,000 Hz.

The speed of sound in air at 20ºC is 343 m/s.

A. Calculate the period of the sound waves of the siren.

B. Calculate the wavelength of the sound waves of the siren.

Problem 3: The jet engine of an airplane produces sound with a wavelength of 0.0429 m. The speed of

sound in air at 20ºC is 343 m/s.

A. Calculate the frequency of the sound waves emitted from the jet engine.

B. Calculate the period of the sound waves emitted from the jet engine.

Problem 4: A spring oscillates 75 times per minute.

A. Calculate the frequency of the spring’s oscillations.

B. Calculate the period of the spring’s oscillations.

Problem 5: The hydrogen atoms on a water molecules vibrate 620,000 times per minute.

A. Calculate the frequency of the vibration.

B. Calculate the period of the hydrogen atom’s vibrations.

Problem 6: An earthquake occurs. The seismic waves (earthquake shaking waves) travel through the

crust at a speed of 5900 m/s (5.9 km/s). The frequency of the earthquake waves is 250 Hz.

A. Calculate the wavelength of the earthquake waves.

B. Calculate the distance that the earthquake waves traveled after

2 seconds

4 seconds

10 seconds

30 seconds

1 minute

Problem 7: An explosion occurs. The sound emitted from the blast has a wavelength of 0.0980 m. The

shock wave created by the blast travels with a speed of 520 m/s.

A. Calculate the frequency of the sound emitted by the blast.

B. Calculate the period of the sound waves emitted by the blast.

C. Calculate the amount of time it takes for the shock wave to travel

1000 m

2000 m

3000 m

4000 m

Conceptual Physics: Unit 4

Homework: Properties of Light

Name: ______________________________________ Block: ____________

Due Thursday, November 14, 2013

Properties of Light

Light Cloze Fill in the blanks with words from the box.

absorb electromagnetic medium opaque

prism rainbow reflects refraction

shadows translucent transparent white

Rainbows form when

sunlight is refracted

by water droplets.

Light is another word for _________________ radiation. The

sun produces _________________ light, which is a

combination of all the colors of light. However, these colors can be

separated using a solid glass triangle called a

_________________. A prism uses the property of

_________________, which is the bending of light as it passes

from one _______________ to another. A _____________is

formed when the sun’s light is refracted through droplets of water

in the atmosphere.

We see objects when light _________________ off of them.

Different objects appear to be different colors because of the way light reflects off of the objects. Blue

objects _________________ every color except blue, which is reflected. Light can also pass

through objects. Objects that allow light to pass through them are _________________. Objects

that blur light as it passes through are called _________________. Objects that block light

completely are _________________. Opaque objects form _________________ under them

when light shines on them.

GAMMA, INFRARED, MICROWAVE, RADIO, ULTRAVIOLET, VISIBLE, XRAY

VISIBLE SPECTRUM: BLUE, GREEN, INDIGO, ORANGE, RED, VIOLET, YELLOW

List the classes of EMR in order from most energetic

to least energetic. List the classes of EMR in order from longest

wavelength to shortest wavelength.

Most energy Longest λ

Lease energy Shortest λ

List the classes of EMR in order from lowest

frequency to highest frequency. List the colors of the visible spectrum in order from

most energetic to least energetic

Lowest f Most energy

Highest f Least energy

List the colors of the visible spectrum in order from

longest wavelength to shortest wavelength. List the colors of the visible spectrum in order from

lowest frequency to highest frequency.

Longest λ Lowest f

Shortest λ Shortest f

Name: ________________________________________________ Block: _______________

Due Tuesday, November 19, 2013.

Conceptual Physics: Unit 4

Diagrams Representing Waves, Sound, and Light

1. In the box below, NEATLY draw a transverse wave. Label the transverse wave with crest, trough, wavelength,

amplitude, and equilibrium position. Draw the transverse wave such that it has 4 complete waves.

2. In the box below, NEATLY draw a longitudinal wave. Label the longitudinal wave with compression, rarefaction, and

wavelength. Draw the longitudinal wave such that it has 4 complete waves.

3. In the box below, NEATLY draw an electromagnetic wave. Label the electromagnetic wave with the electric field and

magnetic field. Draw the electromagnetic wave such that it has 4 complete waves.

4. The diagram below shows three different incident rays of

light moving toward a mirror. NEATLY draw the reflected

ray of light for each of the incident rays of light.

5. The diagram below shows a double convex lens. NEATLY

draw parallel rays of light entering the lens. Draw the

refracted rays of light exiting the other side of the lens. Show

the position of the focal point and indicate the focal length.

6. The diagram below shows a double convex lens. NEATLY

draw parallel rays of light entering the lens. Draw the

refracted rays of light exiting the other side of the lens. Show

the position of the focal point and indicate the focal length.

7. The diagram shows a ray of light about to penetrate through

the boundary into water. Draw the refracted ray of light.

8. The diagram below shows waves approaching an obstacle.

Draw the diffracting waves after the incoming waves impact

the obstacle.

9. The diagram below shows waves approaching a barrier

with a small opening. Draw the diffracted waves after the

incoming waves pass through the opening.

Mirror

A

B

C

Air

Water

Name: _____________________________________________________ Block: _______________________

Conceptual Physics: Unit 4

Properties of Waves, Sound, and Light

Fill in the blank. Write the correct term on the line to the left of the question.

1 What is the total collection of all wavelengths of visible light?

2

What is the total absence of visible light; total absorbance of all frequencies of visible

light.

3 What are the two forces in an electromagnetic wave?

4 What is a triangular glass that separates the colors of the visible spectrum by refraction?

5 What is a repeating back-and-forth motion by a molecule or string at regular intervals?

6

In an electromagnetic wave, what is the compact packet of energy that behaves like a

particle but has no mass?

7 Which type of mechanical wave is also known as a compression and expansion wave?

8 What is the only medium through which sound waves cannot travel?

9 What is the maximum displacement of a wave from its equilibrium position?

10 What is the number of waves, vibrations, or cycles per second?

11 What is the distance between two identical positions on two consecutive waves?

12 What is the amount of time it takes for one wave, one vibration, or one cycle to occur?

13 What is any traveling disturbance through matter that carries energy?

14 Which class of EMR has the longest wavelength?

15 Which class of EMR is the signature light for heat?

16 What are the three parts of an EMR wave?

17 EMR is the abbreviation for ________.

18 What is it called when light is given off by matter?

19

Any material in which light will pass through the surface, but it becomes distorted—

images are blurred and cannot be seen clearly on the other side.

20

Any material that light will not pass through the surface—light is either absorbed or

reflected at the surface.

21

Any material through which light will pass with no obstruction—images can be seen on

the other side.

22 What is the assimilation of radiant energy or light by matter?

23 When matter absorbs light, which type of energy is always created?

Characterize the properties of the four wave functions shown below.

Wave A Wave B

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

10

0

10

5

11

0

11

5

12

0

Distance (meters)

Dis

pla

cem

ent

(met

ers)

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

10

0

10

5

11

0

11

5

12

0

Distance (meters)

Dis

pla

cem

ent

(met

ers)

Wave C Wave D

-8.0

-7.0

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 5 10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

10

0

10

5

11

0

11

5

12

0

Distance (meters)

Dis

pla

cem

ent

(met

ers)

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

10

0

10

5

11

0

11

5

12

0

Distance (meters)

Dis

pla

cem

ent

(met

ers)

All of the waves have the same wave speed. They travel 120 meters in 1 second: 120 m/s.

Wavelength (m) Amplitude (m) Frequency (Hz) Period (s)

Wave A Wave B Wave C Wave D

CONCEPTUAL PHYSICS: UNIT 4

True and False: Properties of Waves, Sound, and Light

Name: ___________________________________ Must be submitted by Wednesday, November 20, 2013

True or False. On the line, write TRUE or FALSE to answer the questions.

An example of a wavelength is trough to trough on consecutive waves.

An example of a wavelength is crest to crest on consecutive waves.

An example of a wavelength is crest to trough on the same wave.

An example of a wavelength is trough to equilibrium position on consecutive waves.

The shorter the wavelengths, the lower the frequency.

The greater the frequency, the shorter the wavelengths..

The greater the frequency, the shorter the period.

The greater the frequency, the longer the period.

The longer the wavelength, the longer the period.

The longer the wavelength, the shorter the period.

An example of wavelength is rarefaction to rarefaction on consecutive waves.

The greater the frequency, the more energy in the waves.

The greater the wavelength, the more energy in the waves.

Electromagnetic waves cannot pass through a vacuum.

Electromagnetic waves can pass through air.

Mechanical waves can pass through a vacuum.

Mechanical waves can pass through solids but not liquids.

The two types of mechanical waves are longitudinal and harmonic waves.

Infrared light has the greatest wavelength.

Microwaves have the shortest wavelength.

Gamma rays have the highest frequency.

Radio waves have the shortest wavelengths.

Red light has greater frequency that blue light.

Infrared light has a greater wavelength than microwave.

The sun emits all classes of EMR.

Sound waves are transverse waves.

Sound waves are longitudinal waves.

Sound waves travel faster than electromagnetic waves.

Sound waves travel faster through air than through water.

Sound waves travel faster through water than through walls.

The greater the frequency, the lower the pitch of sound.

The greater the frequency, the lower the energy of the sound waves.

The sound you hear is because of the rarefactions.

Condensations make up the wave fronts.

Objects that travel faster than the speed of sound are supersonic.

Objects that travel faster than the speed of sound are ultrasonic.

Sound with frequency greater than human hearing are supersonic.

Sound can travel through solids and gases, but not through liquids.

Sound travels faster through cold air and slower through warm air.

Diffraction is when waves bend or spread out after moving around an obstacle.

Light passes from air into water. The light waves slow down.

Light passes from glass into air. The light waves slow down.

Sound passes from water into air. The sound waves slow down.

Sound waves pass from air into water. The sound waves slow down.

Resonance occurs when light waves change direction and speed as they pass through a boundary

between two mediums.

Refraction only occurs to rays of light.

A double convex lens is an example of a diverging lens.

A double concave lens is an example of a converging lens.

A lens functions because of diffraction.

A reverberation occurs when the emitted sound overlaps with the echo returning, the two cannot be

totally differentiated.

Light travels faster than sound.

The farther you stand from a speaker, the lower the volume of the sound.

The power of light released by a light source is called radiance.

Scattering of light will reduce the brightness of light observed.