NOTES 12/4/2012 -12/7/2012
¨Chapter 15 Electricity
¨15.1 Electric Current
¨Electrons in Motion
¨Current electricity is the flow of electrons or other charged particles from one place to another
¡Electricity is either static electricity or current electricity depending on whether the electrons are at rest or in motion.
¨Direct and Alternating Current
¨Direct current is electricity that is flowing in only one direction without reversing.
¨Alternating current is electricity that flows first in one direction and then the other reversing at regular intervals.
¨Causes of Electron flow
¨Electrons move from one place to another because of the attraction and repulsion between electric charges.
¨A wire carrying a current does not have overall charge itself, as electrons move within the wire their charge is balanced by the positively charged nuclei.
¨Voltage, Current, and Power
¨Voltage is the force that electric current flows; it is determined by the difference between the charges.
¡SI unit of voltage is the volt
¨Current is the rate of the charge flow.
¡Si unit of current is the ampere
¡Current is the rate of charge flow not the total amount of charge transferred over a period of time.
¨Power is energy used per unit of time. It depends upon both the voltage and the amount of current.
¡Power = Voltage x Current
¡SI unit of power is the watt
¨Measuring Energy Usage
¨The amount of electrical energy used by an electrical device depends on two factors:
¡The power of the electrical device
¡Length of time that the device operates
¨Since the electricity expended depends on the amount of power used and the time, electric companies charge for electricity by the kilowatt-hour, the amount of energy used when 1kW of power is used continuously for 1 hr.
¨Conductors are materials through which current flows easily
¨Insulators – are materials through which current does not flow
¨Resistance is the amount a certain object hinders electron flow
¡Unit of resistance is the ohm. Ohmmeter is used to measure resistance.
¨Energy used to overcome resistance is converted into heat called Joule heat
¨Factors affecting resistance
¡Type of material
¡Diameter of the conductor
¡Length of the conductor
¨Superconductor is a material that allows current to flow through it with no resistance
¨Ohm’s law states that the current flowing through a conductor is directly proportional to the voltage and inversely proportional to the resistance.
¡Voltage = Current x Resistance
¡Ohm’s law makes it possible to limit the flow of electricity in a conductor by adding resistance
¡A device designed to add resistance to a circuit is a resistor.
COMPLETE THE 15.1 SECTION REVIEW
¨15.2 Electric circuits
¨An Electric Circuit is the path that an electric current follows.
¨A simple electric circuit contains 3 parts
¡A source of current which may be a battery or generator
¡A set of conductors usually wires to carry the electrons around the circuit
¡A load, a device that transforms the energy of the electric current into another useful form of energy
¨Closed and Open Circuits
¨Electric current requires a complete circuit in order to flow
¡Closed circuit is a circuit that contains a complete path for electrons to flow from the source of current, through the load, and back to the source.
¡Open circuit occurs if a gap is made in the circuit and electrons cannot cross it and the circuit ceases
úA switch is a device that opens or closes a circuit to control the flow of current through a circuit.
¨A current follows the path of least resistance. A short circuit occurs when electricity has the opportunity to take a “shortcut” through a circuit avoiding the load.
¨Ohm’s law reveals why it is dangerous
¨A fuse is a narrow strip of metal housed in a protective insulated case
¨The circuit breaker is an automatic switch that opens the circuit when current flowing through it exceeds a predetermined amount.
¨Fuses and circuit breakers guard against an overloaded circuit, a situation that occurs when too many appliances and connected to a circuit at one time, forcing the wires of the circuit to carry more current than they can safely handle.
¨Series Circuit is a circuit in which the loads are arranged so that the electric current flows through each load one after another.
¡The current is the same in all parts of a series circuit
¡The total resistance of a series circuit equals the sum of the resistances of the individual resistor (loads)
¡The total voltage of a series circuit equals the sum of the individual voltages. The voltage is divided among the loads
¡Ohm’s law applies to any series circuit or any part of a series circuit
¨Parallel Circuits is a circuit in which the loads are arranged in separate branches of the circuit and the current is divided among them
¡The total current of a parallel circuit equals the sum of the individual currents. The current is divided among the loads
¡The reciprocal of the total resistance of a parallel circuit equals the sum of the reciprocals of the resistances of the individual resistors (loads)
¡The voltage is the same in all branches of a parallel circuit
¡Ohm’s law applies to any parallel circuit or any part of a parallel circuit.
¨Complete the 15.2 Section review
¨15.3 Using Electricity
¨Light from Electricity
¨Incandescent lamp was the first electric light that was suitable for household use
¨Fluorescent lamp is an electric discharge lamp produces light by passing an electric current through a long tube filled with a low-pressure mixture of mercury vapor and argon
¨Compact fluorescent lamps coiled tubes about the size of a regular bulb operate as long fluorescent lamps but save about ¼ energy and have longer lifespan. Disadvantages are: they are more expensive and mercury inside can be hazardous if broken.
¨Neon lamp is an electric discharge lamp filled with neon gas instead of mercury vapor.
¨Light emitting diodes (LEDs) combination of semiconductors that produce light at a low temperature when an electric current flows from one material to the other. They emit light when a direct electric current is applies
¨Motion from Electricity
¨Electricity can produce magnetism and magnetism can produce electricity
¡Solenoids a simple device that converts electricity to back and forth motion. It is the simplest form is a wire coil with an iron bar free to slide back and forth
¡Telegraph is a device for communicating over long distances by means of electromagnets. It consists of
¨Motion from Electricity
¨Electricity can produce magnetism and magnetism can produce electricity
¡Solenoids a simple device that converts electricity to back and forth motion. The simplest form is a wire coil with an iron bar free to slide back and forth
¡Telegraph is a device for communicating over long distances by means of electromagnets. It consists of a switch, or key, at one end of a long wire and an electromagnet at the other end. When the key was pressed to electromagnet attracted a piece of metal which snapped against the electromagnet with a click. Morse code was a special code of long and short clicks so that the messages could be transmitted in either direction
¡Relay is a small current applied to the electromagnet in a relay that generates a magnetic field that closes the switch. They are used in home appliances, car ignitions and power plants where current must be switched off and on automatically.
¡Loudspeaker also uses electromagnetism. Loudspeakers coverts pulses of electricity into sound waves. They are an important part of the telephone.
¨The Electric Motor
¨Electric motor is the most important device for converting electricity into motion
¨An electric motor operates according to the law of magnetic pole: unlike poles attract and like poles repel.
¨A simple electric motor contains an electromagnet (called the armature) mounted on a shaft and free to rotate.
¨Changing the direction of the current in the armature each half-turn causes the armature to rotate continuously.
¨DC motor is a device that the motor operates is attached to the end of the motor’s rotating shaft. AC motor is similar to DC but does not need a commutator because alternating current already alternates direction.
¨Complete the 15.3 Section review
¨15.4 Producing Electricity
¨Sources of Electricity
¡Motion in a magnetic field
¨Electrochemical cell is any device that produces electricity by means of a chemical reaction
¨2 major categories of electrochemical cells
¡Voltaic cells – not designed to be recharged
¡Storage cells- can be recharged by sending a current through them backward
¨Cells can be arranged in a series to boost the voltage
¨Battery is a group of electrochemical cells connected together as a source of current
¨Cells can be arranged in parallel to boost the maximum available current
¨Hans induction is the ability of magnetism to conduct Christian Oersted demonstrated that an electric current can directly produce mechanical motion by generating a magnetic field
¨Michael Faraday discovered that the process also works in reverse: mechanical motion can directly produce electric current by the magnetic force.
¡Electromagnetic induction is the ability of magnetism to convert mechanical motion into electric current
¡Faraday made this discovery by observing a coil of wire connected to a galvanometer (a device that detects and measures very small electric currents.
¡Faraday also discovered that the conductor must “cut” the lines of magnetic flux to produce a current
¡The strength of an electromagnetically induced current can be increased in several ways
úMoving the magnet more quickly
úIncreasing the strength of the current by increasing the strength of the magnet
¡Generator is a device that uses electromagnetic induction to produce electricity
¡The invention of the electric generator made the production of large quantities of electricity practical
?Chapter 14 Magnetism
?14.1 Magnets and Magnetism
?The Nature of Magnets
?Magnet is an object capable of attracting materials such as iron or steel by magnetic force
?Magnetism is the property of attracting objects by the magnetic force.
?Lodestone (naturally occurring magnet) served as a natural compass that consistently pointed north
?Poles are regions of concentrated magnetism
?North pole – magnetic pole that points north
?South pole - magnetic pole that points south
?Law of magnetic poles states that unlike poles attract each other, but like poles repel each other
?Magnetic poles always exists in pairs
?Magnetic field is the region surrounding a magnet in which other objects are affected by magnetism
?The shape of a magnetic field can be formed by sprinkling tiny iron filings around a magnet. The filings group into clumps and line up in the direction of the magnetic field and follow imaginary lines of flux that indicated the direction of the magnetic field. The lines of flux are continuous and are closest to the poles.
?Law of Magnetic Force
?Law of Magnetic force (Coulomb) states that the force between two magnetic poles is directly related to the product of the pole strengths and inversely related to the square of the distance between the poles.
?The extent to which a material can absorb or channel lines of magnetic force is called permeability. The higher the permeability of a substance the more easily it is magnetized.
?Whether a permeable material increases or decreases the magnetic force between two objects depends on its placement.
?Complete the 14.1
Section Review page 330
?14.2 Understanding Magnetism
?Magnetic fields are produced by the motion of electrons (and other charged particles).
?Each electron has 2 types of motion: a spinning motion about an axis and an orbital motion around the nucleus of the atom: these motions are described by the electron’s 4 quantum numbers.
?Electron spin is the most important cause of magnetism in magnetic materials.
?Sources of Magnetism in Atoms
?1. A strong magnetic field is produced by the spin of electrons on their axes
?2. A weaker magnetic effect is produced by the orbital motion of electrons about the nucleus of the atom.
?3. A very weak magnetic effect is produced by the spin of an atom’s nucleus on its axis.
Domain is a group of aligned atoms having a single magnetic field.
Our understanding of how magnets works depends upon the Domain Theory which states that the magnetic field of a magnet is the sum of the fields of thousands of magnetic domains each composed of billions of atoms containing unpaired spinning electrons.
A magnetic substance forms a magnet only if its domains are mostly aligned.
Types of Magnetic Materials
Diamagnetic – Substances with no unpaired electrons they are always slightly repelled by either pole of a magnet this effect is usually too weak to be noticeable
Paramagnetic – A material weakly attracted to a magnet and have only one unpaired electron per atom
Ferromagnetic – Substances that have several unpaired electrons per atom making them strongly attracted to magnets
Ease of Magnetization
Magnetically soft – substances that can be quickly magnetized even in a weak magnetic field; these substances are easy to align but lose their alignment easily.
Temporary Magnet – a soft magnet made from a magnetically soft material which quickly loses it magnetism when the magnetic field is removed
Magnetically hard – materials whose domains strongly resist changes in the direction of their magnetic fields
Permanent magnets – substances that retain their magnetism for a long time and are made from magnetically hard materials
Methods of Magnetization
Magnetizing by contact – direct contact of a metal with a magnet transferring magnetism to the metal; can be either temporary or permanent
Magnetizing by induction – Temporary magnetization caused by placing an object within a magnetic field but not touching the magnet
Magnetizing by electricity – Electricity and magnetism are closely related: both are caused by electrons. Whenever electricity flows through a wire a magnetic field is produced around the wire. The substance can retain its magnetism after the electric current is stopped.
Electromagnet – a device that produces a strong magnetic field when electricity passes through it. The core is the magnetically soft material that is placed within the coils of an electromagnetic in order to strengthen its field
The strength of the magnetic field produced by an electric current is directly related to the square of the current
The strength on an electromagnet is also proportional to the number of loops of wire in the coil
Although permanent magnets do not easily lose their magnetism under certain conditions they can lose strength or even demagnetized altogether
Curie point – the temperature at which a ferromagnetic material’s domains disappear
Deflecting force – the force existing in a magnetic field that causes a moving electric charge to deviate from its original path
Complete the 14.2 Section Review on pg 338
?14.3 Earth as a Magnet
?A magnetic compass is a navigational device consisting of a magnet free to swing horizontally so that it always points north
?Our Magnetic Planet
?William Gilbert discovered that a compass points north because it is guided by the earth’s magnetic field.
?Gilbert shaped a lodestone into a small sphere to represent the earth and showed that a compass placed anywhere on the surface of his terrella always pointed to the sphere’s magnetic poles lining up with the lines of magnetic flux surrounding the lodestone.
?In 1600 Gilbert published his findings in his book De Magnete.
?The magnetic poles of the earth do not coincide exactly with the geographic poles. They are called north and south because of their geographic locations not because of their magnetic properties
?North pole of a compass points to the magnetically south pole of the earth making what we know as the earth’s north magnetic pole actually a “south-seeking” pole. The south magnetic pole is actually a “north-seeking pole”.
?Declination and Inclination
?A compass needle is usually a few degree off from true north. This deviation is called angle of declination
?A map can show the angle of declination for the entire earth using isogonic lines which connect points of equal declination
?The line connecting all points where a compass needle points true north is called the agonic line
?Inclination is the phenomenon that the north-seeking pole dips or points downward toward the earth in the Northern Hemisphere
?Some maps are constructed with irregular horizontal lines called isoclinic lines that connect locations having equal inclination
?At either of the magnetic poles the inclination is 90 degrees or straight down.
?The imaginary magnetic equator circles the earth halfway between the two magnetic poles.
?Devices that measure the strength of magnetic materials or detect shifts in such fields are called magnetometers
Magnetosphere is the extent of the planet’s magnetic field in space. It is not spherical but is shaped somewhat like a comet.
Solar wind is a stream of plasma that emanates from the sun traveling at high speeds that distorts the magnetosphere.
The outer boundary of the magnetosphere is the magnetopause
Van Allen radiation belts are two vast doughnut-shaped belts of high speed charged particles. These particles are formed by some of the charged particles of the solar wind penetrating the magnetosphere but being trapped in the magnetic field above the earth.
Aurora is a display of shimmering light caused from when high speed particles spiral into the upper atmosphere above the earth they crash violently into molecules of air.
In the northern hemisphere it is called the aurora borealis or Northern lights in the Southern hemisphere it is called the aurora Australis or southern lights
Earth is not the only large natural magnet in the solar system
Mercury is about one hundredth the strength of Earth’s
Venus and Mars are not magnetic but the gas giants (Jupiter, Saturn, Uranus, and Neptune) have strong magnetic fields.
The sun also possesses a magnetic field partly responsible for solar flares, solar prominences, and the sunspot.
Complete the 14.3 Section Review and the
Chapter 14 Chapter Review (Identify)
Ch 13 Electrostatics
13. 1 Introduction to Electrostatics
History of Electrostatics
Electrostatics is the study of nature, behavior, and uses of static (stationary) electricity and related phenomena.
Thales of Miletus believed that the forces were contained within the objects themselves and was natural, observable, and predictable rather than miraculous and mystical.
William Gilbert was the first to discover that amber is not the only source of mysterious force. He named these forces electrics.
Benjamin Franklin discovered that static electricity exists in two forms positive charges and negative charge. He also discovered that lightning is caused by static electricity in clouds.
The Nature of Static Electricity: Electric Charge
Protons and electrons possess a certain amount electric charge, a property that allows them to attract or repel other charged particles by the electromagnetic force.
There are two opposite types of charge, a proton possesses positive charge, and the electron possess negative charge
Electricity is the interactions between electrons and other charged particles
An atom or other object with an equal number of positive and negative charges is neutral.
Equal and opposite charges neutralize each other when they come in contact
Electric Charges are commonly called static electricity, the simplest form of electricity
Whenever a rod with a positive charge is built up in two objects by friction, one object is charged negatively and the other is charged positively
The region around a charged object in which other objects are attracted or repelled by an electric force is an electric field
Although invisible such a field can be mapped with imaginary line of force which indicate the direction and strength of field
The more electrons an object gains or loses the stronger its charge
The SI unit of electric charge is the coulomb
Law of Electric Charges states that opposite charges attract each other but like charges repel each other
If two plates of opposite charges are close to each other they form a uniform field in which the strength of the field is equal throughout
Law of Electric force states that the strength of the attraction or repulsion between two charged objects is directly related to the strength of the charges and inversely related to the square of the distance between them
Complete the 13.1 Section Review
?13.2 Transferring Charges
?Sharing a Charge
?Electric charge can be transferred between objects in several ways
?Conduction (direct contact) – most common way. Because the charged object shares its charge with the uncharged object a charge imparted by conduction has the same sign (positive or negative) as the original charge
?Because electrons physically move from one object to the other, charging by conduction is permanent. (if the air is humid the charge will slowly leak away in the air)
?Law of Conservation of Charge states that the total charge is the same before and after an interaction
?Grounding is the process of diverting unwanted electric charge directly into the earth
?Inducing a Charge
?Temporary transfer – electric charge can also be imparted at a distance without direct contact between the objects by the process of induction (transfer of energy by an object brought near but not touching)
?Charging by induction produces 2 charges instead of one
?Charging by induction is usually temporary
?Charging by induction and charging by conduction share one similarity : they both obey the law of conservation of charge
?A permanent charge can be produced by combining induction and grounding
?A neutral atom can gain or lose electrons and become an ion (an atom or group of atoms that has an electric charge)
?Charge may be carried by anions (negative ions) and cations (positive ions) by electrons freed from parent atoms. The flow of charge from one place to another is current: can be found in gas, liquids, or solids.
?Electroscope is a simple device that uses the laws of electrostatics to detect small electric charges
****Complete the 13.2 Section Review****
Notes for Monday November 26, 2012
Otto von Guericke built the first electrostatic generator (a device that produces static electricity)
Guericke discovered that if he generated enough electricity the surface of sulfur sphere would begin to glow therefore he became the first person to witness electroluminescence.
Van de Graaff generator
The most common electrostatic generator is the Van de Graaff generator invented by American scientist Robert Van de Graaff
It illustrates that electric charge always moves to the outside of the charged object.
The charge exists solely on the surface of a conductor, the shape of the conductor affects the distribution of the charge:
If the conductor is a sphere the charge distributes itself uniformly over the surface
If the conductor is not a sphere the charge is more concentrated whenever the contour is a sharper curve most concentrated whenever the contour comes to a corner or point.
Nature’s electrostatic generators
Thunderstorms are one of nature’s most common electrostatic generators:
An initial stream of electrons called a stepped leader moves from the cloud to the ground
The positive charge on the ground attracted by the approaching stepped leader launches upward in a positive streamer
The upward flow of positive charge called the return stroke forms a brilliant flash of light
If enough charge is available a second leader called a dart leader
Franklin’s kite experiment
Benjamin Franklin discovered that if a cloud’s electric charge could be safely dissipated into the ground lightning strikes could be prevented or controlled.
He invented the lightning rod, a device for protecting buildings and other structures from lightning strikes
The Leyden jar was an early device used to store an electric charge.
Today the Leyden jar is considered an early type of capacitor, a device used to store a static electric charge.
Using Static Electricity
Xerography is an electrostatic method of producing images on paper.
Electrostatic air filters use friction from the passing air to obtain a negative charge.
Many car manufacturers also use static electricity when painting cars.
Complete the 13.3 Section Review
Notes Ch 12 Week of 11/13-11/16
ÒChapter 12 Light and color
Ò12.1 The Nature of Light
ÒTheories of light
ÒLight as a Particle
ÉParticle Theory of Light – (Newton) Idea that light is a stream of tiny particles emitted by a light source.
ÒLight as a Wave
ÉWave Theory of Light (Hooke and Huygens) Idea that light actually consists of waves not particles
É(Maxwell) Demonstrated that light consists of two transverse waves oscillating at right angles to each other. These two waves act together as a single electromagnetic wave. Electromagnetic waves can travel through empty space.
É(Hertz) demonstrated the existence of invisible electromagnetic waves. Built a device to produce an oscillating electric current in a length of wire. Hertz device constituted the first radio transmitter and receiver. He showed that radio waves have the same properties as light
ÒWavelength and Frequency
ÉElectromagnetic waves travel at 300,000,000m/s (180,000mi/s)
ÉSpeed= wavelength x frequency. Formula shows that the frequency of an electromagnetic wave is inversely related to its wavelength; low-frequency waves have long wavelengths and high frequency waves have shorter wavelengths.
ÉPhotoelectric effect (Hertz) light above a certain frequency can knock electrons loose from atoms of certain metals
ÉQuantum theory – states that light has both a wave nature and a particle nature. This property of light is called the wave-particle quality
ÐLight exists as tiny bundles or packets of energy called photons
ÐWhen interacting with matter photons act like particles, but when traveling through space photons act like electromagnetic waves
ÒLight and color: Perceiving frequencies and the visible spectrum
ÒElectromagnetic waves that the human eye can perceive are visible light
ÒIf all the frequencies of electromagnetic radiation from 400THz are arranged in order of gradually increasing frequency, the human eye can see six basic colors: red, orange, yellow, green, blue, and violet (the visible spectrum)
ÉLowest frequencies are seen as red
ÉHighest frequencies are seen as violet
ÉGreen is in the middle of the visible spectrum
ÉWhite can be thought of as a mixture of the colors of light (when all frequencies enter the eye at the same time, it sees white)
ÉWeaker white light is seen as gray
ÉWhen no frequencies of visible light enter the eye it perceives black (absence of color)
ÒLight and color : Newton’s discovery And adding and subtracting colors
ÒNewton realized that a prism separates white light into its component colors by refracting (bending) the light that passes through it
ÒAdding color- various combinations of red, green, and blue light can create the illusion of almost any color. Because they add together to produce the illusion of different colors they are referred to as additive primary colors of light.
ÒSubtracting color – Illusions of color can also be produced by subtracting certain colors from visible light by means of pigments. Magenta, cyan, and yellow are called the subtractive primary colors.
Ò12.2 Behavior of light
ÒLight exhibits characteristics of both particles and waves
ÒThe wavelike properties of light – reflection, refraction, interference, and diffraction- are the most familiar
ÒReflection of light
ÒLike any other wave, light can be reflected when it strikes an obstacle
ÒLight waves obey the law of reflection, which states that the angle of incidence equals the angle of reflection
ÒMirrors can form two types of images
ÉVirtual image – appears to be behind the mirror (no light passes through the image)
ÉReal image – forms in front of mirror
ÒThere are several types of mirrors but spherical are the most important
ÉSpherical mirrors – those that form a portion of a spherical surface
ÐIf the reflecting side is on the inside of the spherical surface the mirror is concave. Can either magnify or reduce the size of the object and can produce either a real or virtual image.
ÐConvex mirror has the reflecting side on the outside of the spherical surface; always produces a virtual image.
ÒRefraction of light
ÒRefraction – Occurs when the path of light waves bends when they cross the boundary between two media
ÉRefracted light waves always bend toward the medium that slows them down.
ÉRefraction is used in eyeglasses, contact lenses, cameras, and binoculars by a special design used to reflect light called a lens. The lens uses thickness and curvature to alter the path of light in different ways.
ÐConvex lens – curves outward and causes rays of light pass through it to bend inward and converge on a point; magnifies objects and is used to correct Presbyopia (farsightedness).
ÐConcave lens – curves inward and causes rays of light passing through it to bend outward, or diverge; causes objects to appear more distant and are used to correct nearsightedness (Myopia)
ÒEffects of refraction
ÒMirage – occurs when the light rays from a distant object are refracted by heated air so that the object appears to be nearby
ÒScintillation (twinkling) – of stars also caused by refraction of light. Starlight traveling through the atmosphere is refracted as it moves between areas of different air density.
ÒRainbow – semicircular arc of colored bands of light in the sky. Formed by millions of airborne water droplets that disperse white sunlight into its component colors.
ÉSecondary rainbow – sometimes appears about 8 degrees higher in the sky than the primary rainbow. Results from light rays that reflect twice within the water droplets instead of once
ÒInterference of light
ÒLight waves commonly undergo interference (the mutual reinforcement or cancellation that occurs when two or more waves meet)
ÒInterference is most commonly seen in connection with thin films such as soap bubbles.
ÒIridescence – process in which colors are produced by interference when light is reflected. Responsible for colors of moth’s scales and color of gemstone opal.
ÒDiffraction of light
ÒObstacle Diffraction- spreading of a wave as it passes by an obstacle or through a narrow gap; not noticeable in everyday experience but is noticeable in formation of shadows
ÉDiffraction blurs the penumbra, lighter edge surrounding the darkest part (umbra) of most shadows
ÒSlit diffraction – diffraction produced by light passing through a narrow slit
É Antinodes (light fringes)-results from constructive interference of light waves coming from different parts of the slit
ÉNode –(dark fringe) light interfering destructively
ÉTool used by scientists produce spectra in the laboratory because diffraction produces a purer spectrum than refraction by a glass prism
ÒThe doppler effect and light
ÒOccurs with light just as it does with sound and other waves.
ÒDoppler effect of light is used to determine the speed of moving objects ranging in size from small particles in fluids to entire galaxies
ÒPolarization of light
ÒA beam of light containing waves that are all aligned in the same direction is said to be polarized.
ÒMethods of Polarization
ÉPolarization of reflection – occurs naturally when a beam of sunlight bounces off a body of water, car windshield, or other smooth flat surface the beam will often become polarized. Can have vertical or horizontal polarization depending on the object’s surface.
ÉPolarization by selective absorption – involves using a special filter to absorb any light waves that are not vibrating in the desired plane. Principle used in polarized sunglasses.
Ò12.3 Electromagnetic Radiation
ÒThe Electromagnetic SpectRum
ÒElectromagnetic Spectrum – an arrangment of all forms of electromagnetic radiation in order of frequency and wavelength
ÒRadio waves – low frequency electromagnetic waves widely used for communication
ÉLowest frequency (30kHz) are produced by long wave radio transmitters (used in ship and airplanes for navigation)
ÉShortwave radio (2-30MHz) – commonly used for international broadcasting
ÉHigher frequency television and FM radio broadcasting uses 88MHz to 108MHz
ÉHighest frequencies of radio waves are used by cellular telephones
ÒMicrowaves are waves of higher frequency and shorter wavelength than radio waves. They range from 1GHz to 300GHz
ÉUses of Microwaves
ÐMicrowave oven uses intense beams of microwaves to cook food. It absorbs the energy of the microwave radiation and becomes very hot as the radiant energy transforms into thermal energy within the food.
ÐCommunication satellites – transmit microwave signals over long distances (television stations radio stations and cellular telephones all use satellites to transmit and receive signals)
ÐRadar – uses reflected radio waves or microwaves to measure the distance and direction of far away objects.
ÒInfrared rays are above the microwaves on the frequency scale and are called that because they are just below red visible light in terms of frequency.
ÒThey transmit radiant heat effectively and are used in heat lamps and infrared video cameras which allow users to see in the dark, fog, or thick smoke.
ÒAbove the infrared portion of the spectrum that is the narrow band of frequencies perceived by the human eye as visible light
ÒExtends from just under 400THz to 800THz
ÒElectromagnetic radiation with a frequency slightly higher than that of visible light is ultraviolet light
ÒCommonly used to sterilize medical instruments
Ò3 Categories of UV radiation: UVA, UVB, and UVC
ÉUVA – has lowest frequency is considered least dangerous
ÉUVB can severely damage or kill cells in the upper layer of the skin largely blocked by the ozone layer
ÉUVC – most powerful and dangerous form of UV radiation, has the shortest wavelength, but is completely blocked by the ozone layer
ÒForm of radiation with higher frequencies than ultraviolet rays that resembles ultraviolet rays in its effect on matter but passes unhindered through wood, paper, and even human flesh.
ÒX-rays are useful because of their ability to easily penetrate materials. Commonly used to diagnose a broken bone.
ÒMost powerful form of electromagnetic radiation. Capable of penetrating nearly all substances including metals.
ÒConsist of electromagnetic waves of extremely high frequency can be harmful to living tissue.
ÒUseful in a medical technique called radio therapy. It focuses beams of gamma radiation to destroy cancerous tumors in a person’s body without harming healthy tissues
ÒGamma radiation are also used in irradiators to sterilize adhesive bandages and other medical supplies
ÒAlso used to sterilize food without adding chemicals or altering the food’s texture.
ÒEnergy of electromagnetic radiation
ÒMax Planck showed that the energy of any electromagnetic wave is directly related to its frequency
ÒSince all electromagnetic waves are composed of photons, the energy of the photon depends on its frequency.
ÒEmissions of photons
ÉElectrons travel around the nucleus of an atom in various electron shells or energy levels
ÉWhen a photon of light strikes an atom, it may be absorbed by an electron which gains one quantum of energy
ÉThis extra energy “kicks” the electron up to a higher energy level.
ÉAs the energy drops back down the electron releases energy and emits a photon as it returns to its original energy level.
ÉExample of this phenomenon
ÐFluorescent objects glow when illuminated by uv light. This occurs because the electrons absorb ultraviolet photons and emit visible-light photons, causing it to glow as it emits light
ÒStimulated emission (Einstein, 1917)
ÉIf an electron already at a higher energy level is struck by a photon, the electron will immediately emit two photons and then fall back down to a low energy level. These two photons will have the same wavelength and frequency, travel in phase, and move in the same direction.
ÉPrinciple of stimulated emission is demonstrated by the laser which generates and amplifies high-energy beams of light.
Ò3 Properties of laser light
ÒLight of a laser is monochromatic (consists of a single frequency)
ÒLaser light is coherent (all the waves are in phase and move in one direction)
ÒLaser light is extremely intense
ÒTypes of lasers
ÒLasers are classified according to how they stimulate the atoms of a substance to produce light and by the substance they use to produce light.
ÉOptically Pumped- atoms of laser are pumped up to an excited state by a flash bulb
ÉHelium neon laser – electrically pumped laser that produces a brilliant red light
ÉArgon laser – most commonly used; uses an intense beam of green light used for many medical applications
ÉCarbon dioxide laser – produces a powerful infrared beam widely used in industry
ÉDye laser – pumps organic dyes to produce several different colors
ÉGallium arsenide laser – tiny laser on a ship; widely used in communication
ÒUses of lasers
ÒCommunication – CD players use a small laser to scan microscopic depressions in the surface of the CD; Fiber optics transmit light through optical fibers
ÒIndustry – powerful lasers are used to slice trough steel and to cut fabric and rubber
ÒMedicine – used in eye surgery can seal small blood vessels and can be used to as scalpels during surgery.
ÒCombat – free electron laser can produce beams of extremely high power . Used to direct “smart bombs”. Lasers have been used to temporally blind an enemy,
ÒA three dimensional image produced by a laser light
Ò12.4 The Speed of Light
ÒThe Constant speed
ÒIn the vacuum of space light travels at a speed of about 229,792,458m/s (186,000mi/s)
ÒSun’s light can reach the earth in about 8 minutes
ÒThe speed of light is in no way affected by the motion of the person or instrument doing the measuring.
ÒThe speed of light in a vacuum is always constant and for this reason is considered a universal constant.
ÒEinsteins Special theory of relativity
ÒAlbert Einstein in 1905 presented the Theory of Relativity which states:
ÉAll motion must be measured relative to some arbitrary reference point
ÉThe speed of light is constant in relation to the observer
ÒConsequences of special relativity
ÉTime dilation (perspective of an outside observer, time slows down for objects moving at high speeds)
ÉLength contraction – at very high speeds objects appear shorter in the direction of motion (called Lorentz contraction)
ÉMass increase – at very high speed from the perspective of an outside observer, the mass of an object moving at high speeds increases
ÒEinstein’s equations show that nothing in the physical universe can travel faster than the speed of light in a vacuum
ÒEinstein’s general theory of relativity published in 1915, proposed that gravity was not mysterious force at all but a result of the geometry of space itself
ÒThis theory also shows that time and length are affected by gravity.