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Sound & LightChapter 15

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Sound Sound waves are

caused by vibrations, and carry energy through a medium.

Sound waves are longitudinal waves.

Speed of sound depends on the medium.

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Speed of Sound Speed of sound at room

temperature is about 346 m/s.

An increase in temperature increases the speed of sound.

Sound waves travel faster in liquids & solids than gases.

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Loudness determined by Intensity Intensity of a sound wave

describes the rate at which a sound wave transmits energy through a given area of the medium.

Loudness depends on the intensity of the sound wave.

The greater the intensity, the louder the sound.

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Relative Intensity The relative intensity

of sounds is found by comparing the intensity of a sound with the intensity of the quietest sound a person can hear.

Relative intensity is measured in units called decibels.

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Pitch The pitch of a sound is

related to the frequency of sound waves.

High pitch correspond to a high frequency, and low pitch corresponds to a low frequency.

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What type of wave is sound?

A. B. C. D.

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000

A. longitudinal

B. seismic

C. surface

D. transverse

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Human Hearing Infrasound is sound

that has a frequency below human hearing.

Ultrasound is sound that has a frequency above human hearing.

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Musical Instruments Fundamental frequency is

the frequency of a standing wave which wavelength is twice the length of a string on an instrument.

Instruments vibrate at their fundamental frequency and whole-number multiples of that frequency called harmonics.

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Instruments Amplify Sound Vibrations from

plucking strings of an instrument are called forced vibrations.

The body of a guitar vibrate at certain specific frequencies called natural frequencies.

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Resonance Resonance is when an

instrument vibrates at its natural frequency.

The natural frequency of an object depends on its: Shape Size mass

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Hearing Sound passing through the

outer ear to the middle ear. The middle ear consists of

the hammer, anvil & stirrup.

The middle ear vibrates the fluids in the cochlea.

The cochlea has tiny hairs that are stimulated and transmit the impulses to the brain.

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Application of Sound Sonar is a system that

determines distance by measuring the time it takes for sound waves to be reflected back from a surface.

Ultrasound is a device that uses the echoes of high frequency ultrasound to produce images of internal organs.

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Assignment: Design an musical instrument from materials you

have at home. Classify it as a woodwind, brass, percussion or string

instrument. Be able to explain the theory behind the instrument

playing different tones. Be able to present music and play it on the

instrument in a recognizable way. Due Monday.

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Light as a Wave Light travels as

transverse waves. Light does not require

a medium. Light waves are called

electromagnetic waves. The wave model is

supported because light can reflect, refract and diffract.

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Light as a Particle In the particle model,

light travel in photons. Photons are considered

particles. Photons don’t have

mass, they are bundles of energy.

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Frequency of Light The amount of energy is

proportional to the frequency of the corresponding electromagnetic wave.

A photon with twice as much energy corresponds to a wave with twice the frequency is in the ultraviolet range.

A photon with half as much energy corresponds to a wave with half as much frequency is in the infrared range.

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Speed of Light Light travels at the

speed of 300,000 km/s. Light travels fastest in

a vacuum and slower in any medium.

Nothing travels faster than light in our universe.

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Intensity of Light The brightness of light

depends on the intensity of the light.

Intensity depends on the amount of light that passes through a certain area of space.

Light spreads out from the source. The farther from the light source, the dimmer the light.

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Electromagnetic Spectrum Electromagnetic spectrum

consist of light of all possible energies, frequencies and wavelengths.

Ultraviolet light has higher energy and shorter wavelengths than purple light.

X-rays has higher energy and shorter wavelengths.

Gamma rays has the highest energy and shortest wavelengths.

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Electromagnetic Spectrum continued Infrared waves has

wavelengths slightly longer than red light.

Microwaves are used for cooking.

Radio waves have the longest wavelengths.

Radar is used to determine location.

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Reflection and Color Reflection occurs as

light hits a barrier and bounces off of the barrier.

The incidence ray is the incoming light waves.

The reflected ray is the light waves that bounce off of the barrier.

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Reflection (continued) The angle of incidence is

defined by the angle between the normal and the incidence ray.

The angle of reflection is defined by the angle between the normal and the reflected ray.

The law of reflection states that the angle of incidence is always equal to the angle of reflection.

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Types of Reflection Smooth reflection

occurs when the light waves hit a smooth surface.

Diffuse reflection occurs when the light waves hit a rough surface and the light waves are scattered.

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Types of Mirrors Concave mirrors are

mirrors that curve inward. These type of mirrors can produce virtual & real images.

Convex mirrors are mirrors that bulge outward. These type of mirrors can produce virtual images.

Plane mirrors produce virtual images.

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Type of Images Real images are

inverted images formed where rays of light meet.

Virtual images are upright images formed where rays of light appear to meet or come from.

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Colors The color we see is the

light being reflected from the object.

Additive primary colors are red, green & blue.

Subtractive primary colors are yellow, cyan and magenta.

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Colors and Pigments If all colors are

reflected, you see white light.

If all colors are absorbed, you see black.

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Refraction Refraction happens

when light waves changes speed as it goes through different mediums.

As light waves change speed the waves bend.

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Effects of Refraction Refraction makes

objects appear to be in different positions.

Refractions in the atmosphere creates mirages.

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Snell’s Law Snell's Law Snell's law

(also known as Descartes' law or the law of refraction), is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves, passing through a boundary between two different media, such as air and glass.

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Total Internal Reflection If the angle at which light

rays meet the boundary between two mediums becomes small enough, the rays will be reflected as if the boundary were a mirror.

This angle is called the critical angle, and this type of reflection is called total internal reflection.

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Lenses A lens is a curved piece

of glass. Lenses can magnify

images. Magnification is any

change in the size of an image compared with the size of the object.

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Type of Lenses Converging lens bends

the light inward that produces a virtual or real image. (convex lens)

Diverging lens bends the light outward and can produce only a virtual image. (concave lens)

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Prisms Prism is a triangular

shaped piece of glass that refracts light.

Prism disperse light. Dispersion is the

separation of light into separate colors because of the differences in wave speed.