Sound waves originate from vibrating objects Sound waves
Sound waves originate from vibrating objects.
Sound waves are longitudnal waves.
The speed of sound depends on the medium. Solids transfer sound the fastest with liquids second. Sound travels slowest in gases with it being transferred faster in hot gases.
Intensity of sound depends on the rate at which sound transmits energy through a medium.
Loudness depends on intensity.
A sound that is twice as intense, however, may not seem twice as loud. Humans percieve sound on a logrhythmic scale called relative intensity. Units of loudness are called decibels.
Pitch is the quality of sound that is related to frequency.
Humans can hear sounds varying from 20 to 20, 000 Hz.
Frequencies lower than the range of human hearing are considered infrasound and those above the range of hearing are considered ultrasound.
Musical instruments come in a variety of shapes and sizes. They are groups according to how they produce vibrations:
By placing your fingers on the strings, you shorten them causing a higher pitch. Standing waves can only exist at certain places on the string.
Wind instruments set up a standing wave with a column of air and the frequency is changed by opening and closing holes which change the length of the column of air.
When struck, a tuning fork emits a tone of one pure frequency. A musical instrument, however, emits a fundemental frequency along with a mixture of whole number multiples of that frequency. This gives the sound of the instrument a certain quality called harmonics.
This process is called resonance and we say that the guitar is vibrating at its natural frequency. This makes a quality guitar play much louder and clearer since the string and the guitar form a standing wave. This would not occur in a guitar that is not carefully designed and built.
Sound waves reflect off solid boundaries. These form echos.
Since one knows the speed of sound, echos can be used to calculate distance.
SONAR uses ultrasound to calculate distance constantly to locate and determine the shape of objects.
Doctors use ultrasound to produce sonograms to study the body.
It has always been an argument among scientists whether to treat light as a wave or as a stream of particles.
In 1801, Thomas Young devised an experiment in which he showed a diffraction pattern of light much like the diffraction of waves on water.
The wave model of light explains much of light’s behavior such as reflection and refraction. It explains light as a beam of electric and magnetic fields that behave as transverse waves.
As scientists studied more about light, they found that they could only explain the photoelectric effect by treating light as a stream of particles or photons.
Most scientists today, treat light as having a dual nature. It can be treated as a particle or a wave depending on the system of study.
The frequency of light determines it’s energy. A photon of UV light has twice the energy of a photon of red light.
The speed of light changes in different mediums. Light travels at 3 x 108 m/s in a vacuum. All other masses such as air, glass, and water have some optical density causing light to travel through them slightly slower.
The number of photons of light emitted from a source and the amount of surface that it illuminates determines the intensity of light.
Light may exist as a number of wavelengths and frequencies.
In order to study the path of light and its changes, it is convenient to represent the wave front direction of light as a line or arrow. We call these arrows rays.
By using rays, we can study geometrical optics by making ray diagrams.
Reflected light obeys the Law of Reflection which states that the angle of incidence equals the angle of reflection.
When you look at yourself in a plane mirror, reflected light creates an upright, virtual image of you in the mirror that has been reversed left to right.
Curved mirrors can: • Distort images • Create real images • Concentrate light into a small bright image
When light crosses and boundary between mediums, it changes speed and is refracted or bent.
When light enters a more optically dense medium, it is bent toward the normal. When it enters a less optically dense medium, it is bent away from the normal.
N = sini sinr n = cvacuum cmedium
Refraction makes objects appear in different positions
Refraction of light creates mirages.
If the angle of the light leaving the glass tube is small enough, it will be reflected back into the glass by total internal reflection.
Fiber optics uses total internal reflection.
A curved piece of glass that refracts light is a lens.
A converging or convex lens causes light rays to come together. A diverging or concave lens causes light rays to spread out.
Lenses can magnify.
The eyes depend on a lens to focus lights on the rods and cones.
Different wavelengths of light are refracted differently. This causes prisms to form color spectrums. This process is called dispersion.
Water droplets in the air can from a rainbow by refraction and total internal reflection.
When white light strikes an object, some combination of red, green, and or blue is reflected. Our eyes percieve these frequencies and the colored image is produced in our brain. These are called the additive primary colors.
In an opposite process, yellow, cyan, and magenta pigments may subtract certain colors from light to produce colored objects. When all of these colors are combined, black is produced.
Lights and pigments can produce some special phenomena. For instance, a green object when viewed under red light looks black.
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