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Chapter 16SOUND & LIGHT

Section 1: Sound

�What are the characteristics of sounds waves?

�How do musical instruments make sounds?

�How do ears help humans hear sound waves?

�How are the reflections of sound waves used?

Intro to Sound wave clip

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Properties of Sound

◦ Sounds waves are longitudinal waves caused by vibrations.

◦ Travel through material medium

◦ In air, sound waves spread out in all directions away from the source.

Properties of Sound

◦Speed of sound depends on the medium◦ Sound waves travel faster in liquids and solids than

gases

◦ In a liquid or solid, the particles are closer together

◦ The vibrations are transferred more rapidly between particles

◦ Some solids (like rubber) dampen vibrations, making waves travel slower. (Sound proofing)

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Speed of sound in Various Mediums

Properties of Sound

Loudness ◦ Determined by intensity

◦ The intensity of a sound describes its loudness

◦ Depends on your distance from the source

◦ The energy of a mechanical wave is determined by amplitude

◦ The greater the amplitude of a sound waves, the louder the sound

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Loudness

Relative intensity-comparing the intensity of a sound with the quietest sound a person can hear, the threshold of hearing

◦ Is measured in decibels, dB

Properties of Sound

�Defined as the perceived highness or lowness

◦ Determined by frequency

◦ A high-pitched note is made by very rapid vibrations (air in a flute)

◦ A low-pitched note is made by slower vibrations (cello strings)

◦ High pitch corresponds to high frequency; low pitch sounds corresponds to low frequency

Pitch

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Pitch

Human hearing◦ Humans hear sound waves in a

limited frequency range

◦ Infrasound (infrasonic) consists of waves where f<20 Hz

◦ Ultrasound (ultrasonic) consists of waves where f>20 000 Hz

◦ Many animals can hear frequencies of sound outside the range of human hearing

◦ Human hearing ranges from 20 Hz

– 20 000 Hz

Frequency Range

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Create frequency of sound scale

Musical Instruments

•All musical instruments rely on standing waves to create sound.

• Vibration of strings, air columns, or membranes

•Harmonics give every instrument a unique sound

•Resonance is an effect in which the vibration of one object causes the vibration of another object at a natural frequency

•Instruments use resonance to amplify sound (guitar)

Tuning Forks Clip

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Hearing and the Ear

�The human ear is a very sensitive organ that senses vibrations in the air, amplifies them, and transmits signals to the brain

�Sound waves cause membranes in the ear to vibrate (eardrum)

�Vibrations pass through three regions in the ear: outer, middle, inner

�Resonance occurs in the inner ear

�The brain interprets impulses from the nerve fibers as a sound with a specific frequency

Hearing Test Hearing test 2

Human ear and hearing

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Ultrasound and Sonar

�Like all waves, sound waves reflect

�The reflection of sound waves can be used to determine distance and to create maps and images

�Sonogram made by different boundary surfaces by a computer. Ultrasound is used to create sonogram ( 1,000,000,000 Hz and 15,000,000 Hz). Not damaging to human cells

�Sonar is a system that uses reflected sound waves to determine the distance to and location of objects

�Sonar is used for underwater location

�Distance can be determined by the formula d=vt

Ultrasound and Sonar

Video

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16.2: The Nature of Light.

�How do scientific models describe light?

�What does the electromagnetic spectrum consist of?

Waves and Particles

Light produces interference patterns like water waves

The wave model of light cannot explain some observations◦ Ex. Light striking a piece of metal causes electrons to

fly

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Photons

Light can be modeled as a stream of particles

◦A photon is a particle of light

◦Photons do not have mass; they are like bundles of energy.

◦The energy of a photon is located in a particular place.

Light

Some scientists believe that light has a dual nature

◦ Light can behave as waves and as particles.

◦ Wave model- interference of light

◦ Particle model-light knocking electrons off a metal plate or light traveling through space

Either model of light yields good results

Both models are accepted by scientists

The model of light used depends on the situation

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Light

◦ Each photon of light can be thought of as carrying a small amount of energy.

◦ The amount of this energy is proportional to the frequency of the corresponding electromagnetic wave.

The energy of light is proportional to frequency

Electromagnetic Spectrum

© 2000 Microsoft Clip Gallery

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Light

◦ In a vacuum, light travels at the same speed,

c =3 x 108 m/s.

�Nothing travels faster than the speed light.

� Light is the fastest signal in the electromagnetic spectrum.

�When light passes through a medium, it travels slower than it does in a vacuum.

�Transparent mediums like air, water, glass

The speed of light depends on the medium

Light travels much faster than sound.

1) Thunder and lightning start at the same time, but we will see the lightning first.

2) When a starting pistol is fired we see the smoke first and then hear the bang.

Why?

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Light

oThe brightness of light depends on intensity.

oIntensity is the rate at which light or any other form of energy flows through a given area of space

oThe intensity of light decreases as the light spreads out.

Characteristics of light Characteristics of light Characteristics of light Characteristics of light

Try this!

Individually draw the Electromagnetic Spectrum from largest wavelength to smallest wavelength.

Compare your illustration with a partner. Together try to come up with the correct order.

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Light

�EM Spectrum- consists of waves at all possible energies, frequencies, and wavelengths

Electromagnetic Spectrum- Types of light

EM clip

Electromagnetic Spectrum-Types of light•Radio waves are used in communication and radar

• Radar determines the distance to and the location of objects

• FM, AM, and TV signals

•Microwaves used in cooking and communication

• Telecommunication over a long distance. (Space to Earth)

•Infrared light can be felt as warmth

• Sun or a heat lamp warm you.

• Keep food warm.

• Weather satellites read (temperature changes) for the tracking of cloud movement

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Visible Light Spectrum

Visible Spectrum – Light we can see◦Roy G. Biv – Acronym for remembering the colors of visible light

◦ Largest to Smallest Wavelength.

R- Red

O- Orange

Y- Yellow

G- Green

B- Blue

I- Indigo

V-Violet

How are the visible

light spectrums above

and below different?

�Ultraviolet light has higher energy and shorter wavelengths than visible light.

�Sunlight contains ultraviolet light (UV rays) (9%)

�UV rays can pass through thin layers of clouds, causing sunburn.

Electromagnetic Spectrum-Types of light

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�X rays and gamma rays are used in medicine.

�Both have higher energy and shorter wavelengths than UV rays

�Gamma rays have the highest energy and the shortest wavelengths.

�Both rays can kill living cells, or turn them into cancer cells.

�Gamma rays can be used to treat cancer, by killing diseased cells

Electromagnetic Spectrum-Types of light

Photon energy increases as ________

◦A. wavelength increases.

◦B. intensity decreases.

◦C. frequency increases.

◦D. frequency decreases.

Try this!

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16.3: Reflection and Color

�How do objects interact with incoming light?

�How can you see an image in a mirror?

�Why do we see colors?

We see things because they reflect light into our eyes:

Homework

Why do we see things?

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Reflection of Light

◦ Every object reflects some light and absorbs some light.

◦ Light can be modeled as a ray ◦ In direction light travels

◦ A light ray travel in straight line through space.

LASER

◦ Geometrical optics is the study of light in circumstances where light behaves like a ray.

ReflectionRough surfaces reflect light rays in many directions.

The angle of reflection is the light rays reflecting off the surface.

The angle of incidence is the light rays striking the surface

Smooth surfaces reflect light rays in one direction.

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ReflectionReflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

The Law of Reflection

The Law of Reflection: the angle of incidence equals the angle of reflection

Both angles are measured from a line that is perpendicular to the surface at the point were the light hits the mirror (normal line)

.

The same !!!

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Mirrors

◦ Form virtual images by reflection.

◦ A virtual image is an image that forms at a point from which light rays appear to come but do not actually come.

◦ Some of the light rays are reflected off the mirror into your eyes.

◦ Perceive an image of yourself

behind the mirror

Flat mirrors

◦Can distort images

◦The normal line points in different directions for different parts of a curved mirror.

◦Two types:

◦ Convex mirrors

◦ Concave mirrors

Mirrors

Curved mirrors

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◦ Curve or bulge out

◦ Produce a stretched out image

◦ Light rays that start out parallel are reflected in different directions

◦ Make objects appear smaller than they actually are

◦ Ex. Mirrors on the passenger side of vehicles

Mirrors

Convex mirrors

◦ Caved in shape

◦ Create real images AND virtual images

◦ A real image results when light rays are focused onto a single point or small area

◦ Ex. Used by telescope

◦ Ex. Radio telescopes gather radio waves from extremely distant objects.

Mirrors

Concave mirrors

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Seeing ColorObjects have color because they reflect certain wavelengths of light

◦ The colors that you perceive depend on the wavelengths of visible light that reach your eyes

Light through a prism separates into a rainbow of colors

White light from the sun contains light from all the visible regions of the electromagnetic spectrum

White light

◦ contains all visible colors - ROY G. BIV

◦ an object…

◦ reflects the color you see

◦ absorbs all other colors

Black is the absence of color; all light is absorbed

o No light gets to your eyes

REFLECTS

ALL COLORS

ABSORBS

ALL COLORS

Seeing Color

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◦ TVs and computers display many different colors by combining light of the additive primary colors, red, green, and blue

◦ Pigments, paints, or filters use subtractive primary

colors yellow, cyan, and magenta.

◦ Creates black

Seeing Color

Colors may add or subtract to produce other colors.

Light Pigment

When mixing pigments,

the color of the mixture

is the color of light that

both pigments reflect.

Adding colors

White light can be split up to make separate colors. These colors can be added together again.

The primary colors of light are red, blue and green:

Adding blue and red makes magenta (purple)

Adding blue and green makes cyan

(light blue)

Adding all three makes white again

Adding red and green makes yellow

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Seeing color

The color an object appears depends on the colors of light it reflects.

For example, a red book only reflects red light:

White

light

Only red light is reflected

A white hat would reflect all seven colors:

A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):

Purple light

White

light

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Color Blindness

◦ one or more sets of cones does not function properly

Test for red-green color blindness.

The retina contains…

◦ Rods - dim light, black & white

◦ Cones - color

◦ red - absorb red & yellow

◦ green - absorb yellow & green

◦ blue - absorb blue & violet

Try this!

Which kind of mirror can create real images?

◦A. A flat mirror

◦B. A concave mirror

◦C. a convex mirror

◦D. A diffuse mirror

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Section 4: Refraction, Lenses, and Prisms

What happens to light when it passes from on medium to another medium?

What happens when light passes through a lens?

How can a prism separate white light into colors?

Refraction of light

•Refraction- Light waves bend, or refract, when they pass from one transparent medium to another

• Objects appear to be in different positions

• Refraction of light in the atmosphere creates mirages.

• Different speeds in air of different temperatures. (light refracted over hot asphalt)

• Light can be reflected at the boundary between two transparent media

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Refraction creates virtual image

Lenses

◦ A lens is a transparent object that refracts light rays, causing light rays to change direction

◦ Rely on refraction

Lenses

◦ A converging lens bends light inward (virtual or real image)

◦ A diverging lens bends light outward (virtual image only)

Co- together Di-apart

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◦Lenses can magnify images.

◦Magnification is any change in size of an image compared with the size of the object.

◦ To see details of an object

Lenses

Lenses

Lenses

The eye depends on refraction and lenses.•The cornea refracts 70% of the light in the eye.

•The curvature of the lens determines how much further the lens refracts light.

•Muscles can adjust the curvature of the lens until an image is focused on the back layer of the eye, the retina

• Rods and cones of the eye, signals are sent to the brain. Images are interpreted.

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Dispersion and Prisms

•A prism is a transparent block with a triangular cross section.

• Different colors of light are refracted differently.

• Light waves with different wavelengths travel at different speeds.

• In the visible spectrum:

• violet –slowest bend more than red-fastest

Prism

• The slower light refracts more when passing between media

Dispersion is an effect in which white light separates into its component colors.

Rainbow are caused by dispersion and internal reflection.

Dispersion and Prisms

We can demonstrate this by splitting white light with a prism:

This is how rainbows are formed: sunlight is “split up” by raindrops.

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Light and Color Video Clip