Chapter 16 Sound and Light

Sound Sound wave: a longitudinal wave that is caused by vibrations and that travels through a material medium A series of compressions and rarefactions Carries energy through medium All sound waves are made by vibrating objects that cause the surrounding medium to move

Sound

Sound The speed of sound depends on the medium Depends on the temperature and the material through which the wave travels Colder temperatures: slower Warmer temperatures: faster Gas (air):slower (346 m/s) Liquids: faster than gas Solids: faster than liquids Some solids like rubber, dampen vibrations so that sound does not travel well (materials like rubber are used for soundproofing)

Sound Speed depends on the temperature and the material through which the wave travels

Sound

Sound

Sound

Sound Loudness is determined by Intensity Intensity depends on the amplitude of the sound wave and your distance from the source of the sound Greater the intensity, the louder the sound Humans perceive loudness on a logarithmic scale A sound seems twice as loud when its intensity is 10 times the intensity of another sound Intensity is measured in units called decibels (dB) An increase in intensity of 10 dB means a sound seems about twice as loud

Sound

Sound

Sound The quietest sound a human can hear is 0 dB A sound of 120 dB is at the threshold of pain Above this value could cause permanent deafness

Sound

Sound Pitch is determined by frequency Pitch is a measure of how high or low a sound is and depends on the sound wave’s frequency A high-pitch sound is made by something vibrating rapidly (high frequency) A low-pitch sound is made by something vibrating slowly (low frequency)

Sound

Sound

Sound

Sound Humans hear sound waves in a limited frequency range Frequency of 20Hz to 20,000Hz Frequency below the range of human hearing is infrasound Frequency above the range of human hearing is ultrasound

Sound

Sound Musical instruments: produce sound through the vibration of strings, air columns, or membranes Strings: when you pluck the string on a guitar, particles in the string vibrate. Sound travels out to the ends of the string and then reflect back toward the middle thus causing a standing wave on the string The two ends of the string are called nodes, and the middle of the string is called an antinode Standing wave exist only at certain wavelengths on a string: fundamental frequency Primary standing wave on a vibrating has a wavelength that is twice the length of the string

Sound

Sound You can change the pitch by placing your finger on the string anywhere on the guitar’s neck A shorter length of string vibrates more rapidly, and the standing wave has a higher frequency with a resulting higher pitch

Sound All musical instrument produce standing waves Drum: standing waves formed on the membranes vibrate Wind instruments: standing waves form in the column of air Opening and closing holes changes the length of the air columns, which change the wavelength and frequency of the standing waves

Sound

Instruments Instruments use resonance to amplify sound when one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion. String and guitar body are vibrating at the same frequency Amplifies the sound Electric guitars do not resonate well and must be amplified electronically

Sound

Sound The human ear is a sensitive organ that senses vibrations in the air, amplifies them, and then transmits signals to the brain Sound waves travel through the outer ear (auditory canal) and cause the eardrum to vibrate The vibration passes from the eardrum through the three small bones of the middle ear (hammer, anvil, stirrup) Stirrup vibrates the membrane of the inner ear (oval window) sending the wavelength through the spiral-shaped cochlea The cochlea contains a long, flexible membrane called the basilar membrane Different parts of the membrane vibrate at different frequencies Hair cells stimulate nerve fibers sending impulses to the brain

Sound Reflected sound waves are used to determine distances and to create images Ultrasound travel through most materials and some are reflected when they pass from one type of material into another Sonar (sound navigation and ranging)is a system used to locate objects underwater

Sound

Sound

The Nature of Light Waves and Particles: it is difficult to describe all the properties of light with a single model The two most common models describe light as a wave or as a stream of particles

The Nature of Light Light produces interference patterns as water waves do

The Nature of Light The model of light as a wave is still used today to explain many of the basic properties of light and light’s behavior Transverse waves that do not require a medium in which to travel Transverse waves described by their amplitude, wavelength, and frequency Light waves are also called electromagnetic waves because they consist of changing electric and magnetic fields

The Nature of Light The particle model of light can explain some effects that the wave model cannot explain Red light cannot knock electrons off the metal plate Blue light can knock electrons off the metal plate The wave model of light cannot explain this phenomenon

The Nature of Light In the particle model of light beam of light is a packet of particles (photons) Not like ordinary matter No mass They are little bundles of energy

The Nature of Light The model of light used depends on the situation Wave model: can explain interference Particle model: explains how light can travel across empty space without a medium

The Nature of Light The energy of light is proportional to frequency of the electromagnetic wave

The Nature of Light The speed of light depends on the medium Resented by the symbol: c 3 x 108m/s ( about 186,000 mi/s) When light passes through a medium, such as air, water, and glass, it travels slower than it does in a vacuum

The Nature of Light The brightness of light depends on intensity Intensity depends on the number of photons per second, or power, that pass through a certain area of space Decreases as distance from the light source increases

The Nature of Light Electromagnetic Spectrum: consists of waves at all possible energies, frequencies, and wavelengths

The Nature of Light Radio waves: TV, AM/FM radio, radar Microwaves: cell phones, ovens Infrared: heat lamps Ultraviolet: sunburn, insect vision X-rays. Gamma rays: medical functions

The Nature of Light

Reflection and Color Every object reflects some light and absorbs some light It is useful to another model for light, the light ray, to describe reflection, refraction, and many other ways light behaves A light ray is an imaginary line running in the direction that the light travels or path of photons

Reflection and Color Reflection of Light: Rough surfaces reflect light rays in many directions Smooth surfaces reflect light rays in one direction Law of reflection:The angle of the light rays reflecting off the surface, called the angle of reflection, is the same as the angle of the light rays striking the surface, called the angle of incidence Both of these angles are measured from a line that is perpendicular to the surface at the point where the light hits the surface (normal)

Reflection and Color

Reflection and Color

Reflection and Color

Reflection and Color

Reflection and Color Mirrors reflect light as described by the law of reflection, and this light reaches your eyes. The type of image you perceive depends on the type of mirror Virtual image: an image from which light rays appear to diverge, even though they are not actually focused there Cannot be projected on a screen Real image: an image that is formed by the intersection of light rays Can be projected on a screen

Reflection and Color Most mirrors are made by coating a piece of glass with a layer of metal. The glass provides the smooth surface necessary for good reflection and protects the metal from becoming scratched and tarnished. Polished plate glass is used for the finest mirrors. A solution containing silver nitrate is poured onto the glass, and a deposit of silver adheres to the glass. The remains of the solution are poured off and the glass is dried. The silvered surface (the back of the mirror) is then coated with a protective substance, such as shellac, to keep the silver from being rubbed off or scratched.

Reflection and Color

Reflection and Color Curved mirrors: imagines created are distorted

Reflection and Color Convex: bulge out Images smaller Passenger side mirror

Reflection and Color Convenience store mirrors are convex. Convex mirrors will produce upright virtual images that are smaller than the object. Their benefit is that they allow you to see more area in the reflection.

Reflection and Color Concave: indented Images larger

Reflection and Color Make up mirrors are concave. Concave mirrors will produce upright, magnified virtual images if the object is between the focal point and the mirror.

Reflection and Color Seeing colors: the colors that you perceive depend on the wavelengths of visible light that reach your eyes Objects have the color of the wavelength they reflect Example: Green leaf reflects green wavelength and absorbs the other wavelengths White: reflects all wavelengths Black: absorbs all wavelengths

Reflection and Color

Reflection and Color

Reflection and Color Mixture of colors produce other colors Additive Primary Colors: red, green, and blue Mixing light of two of these colors produces the secondary colors yellow, cyan, and magenta Mixing light of the three primary colors produces white light

Reflection and Color

Reflection and Color Because filters and pigments absorb light, the opposite effect happens when they are mixed. The Subtractive Primary Colors-yellow, cyan, and magenta-can be combined to create red, green, and blue If filters or pigments of all three colors are combined in equal proportions, all visible light is absorbed No light gets to your eyes, so you see black Black is not a color, it is the absence of color

Reflection and Color

Refraction, Lenses, and Prisms Light waves bend, or refract, when they pass from one transparent medium to another

Refraction, Lenses, and Prisms When light moves from a material in which its speed is high to a material in which its speed is lower, such as from air to a glass the ray is bent toward the normal

Refraction, Lenses, and Prisms If light moves from a material in which its speed is low to one in which its speed is higher, the ray is bent away from the normal

Refraction, Lenses, and Prisms Refraction makes objects appear to be in different positions

Refraction, Lenses, and Prisms

Refraction, Lenses, and Prisms

Refraction, Lenses, and Prisms

Refraction, Lenses, and Prisms A mirage is a virtual image that is caused by refraction of light in the atmosphere The air temperature affects the speed at which light travels. When light from the sky passes into the layer of hot air just above the asphalt on a road, the light refracts and bends upward away from the road. This refraction creates a virtual image of the sky coming from the direction of the road. Your mind visualizes water.

Refraction, Lenses, and Prisms

Refraction, Lenses, and Prisms

Refraction, Lenses, and Prisms Lenses: when light passes through a medium that has a curved surface, a lens, the light rays change direction.

Refraction, Lenses, and Prisms Convex lens: converging lens When light rays pass through a lens that is thicker in the middle, the rays are bent inward

Refraction, Lenses, and Prisms Concave lens: diverging lens When light rays pass through a lens that is thicker at the ends, the rays are bent outward

Refraction, Lenses, and Prisms Microscope use a series of convex lens to magnify the specimen Image

Refraction, Lenses, and Prisms Human eye depends on refraction and lenses

Refraction, Lenses, and Prisms

Refraction, Lenses, and Prisms Prism: separates white light into its component colors Air droplets in the air can also separate the color in white light to produce a rainbow

Refraction, Lenses, and Prisms Different colors of light are refracted by different amounts Light waves travel at 3.0 x 108 m/s in a vacuum When a light wave travels through a medium, the speed of the light waves depends on the light wave’s wavelength Violet waves have a shorter wavelength and travel slowest Red waves have a longer wavelength and travel the fastest Because violet light travels slower than red light, violet light bends more than red light when it passes from one medium to another This effect is called dispersion

Refraction, Lenses, and Prisms Rainbows are caused by dispersion and reflection