exam 3 study guide
exam 3 study guide Phys 100
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This 0 page Study Guide was uploaded by Rebeca Cotton-Baez on Sunday December 6, 2015. The Study Guide belongs to Phys 100 at State University of New York at Potsdam taught by Dr. Lee in Spring 2015. Since its upload, it has received 12 views. For similar materials see Physical Science in Physics 2 at State University of New York at Potsdam.
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Date Created: 12/06/15
Chapter 6 Core concept Electric and magnetic elds interact and can produce forces 1 Electric charge q unit coulomb c see slide 2 The kind of charge positiveproton Negativeelectron Unit of charge coulomb 0 Equivalent to charge of 624x10quot18 0 Metric unit of charge 0 Electron charge 0 Fundamental charge 0 Smallest seen in nature 0 Quantity of charge and the number of electrons An electron charge can be produced by friction contact inductionpolarization Slide 3 Charges in matter lnseparable property of certain particles Electrons negative electric charge Protons positive electric charge Charge interaction 0 Electric force 0 quotlike charges repel unlike charges attractquot lons non zero net charge from lossgain of electrons Slide 11 Coulumb s law Relationship giving force between two charges Similar to Newton s law of gravitation K versus G implies gravity weaker Equation 62 Charge interaction like charges repel unlike attracts 61 Quality of charge of electrons electron charge qne e 16x10quot19 C Example 1c n16x10quot19 C 16x10quot19c 16x10quot19c n 1 16x10quot19 n624x10quot18 Iclicker questions 1 In an experiment in the late 1800 s JJ Thomson discovered that all matter contained negatively charged particles These particles were named after the Greek word for amber Today these subatomic particles are named C electrons 2 A common fundamental property of both electrons and protons is A electric charge Static Electricity Electrostatic charge 0 Stationary charge con ned to an object 0 Charging mechanisms 0 Friction 0 Contact with a charged object o Polarization reorientation induced without changing net charge 3 An electrostatic charge commonly called static electricity can be produced A By transferring electrons through friction B By transferring electrons direct contact between the objects C By induction which redistributed electrons through a material gt D as a result of any of the above Electrical conductors and insulators Electrical conductors o Electrons are free to move throughout the material 0 Added charge dissipates 0 Examples metals graphite carbon 0 Electrical insulators 0 Electron motion restricted o Added charge tends to remain on object 0 Examples glass wood diamond carbon Semiconductors o Conductinsulate depending on circumstances 0 Applications computer chips 3 materials conductors insulators and semiconductors q repels q q attracts q q repels q 4 A conductor is a material which has electrons that are free to move Which of the following is a conductor BSHverspoon 5 Electrical charge is Is measured in units of coulombs Of an electron is 160x 10quot19 Of an electron cannot be divided Of 1 coulomb equals the charge of 624x10quot18 Slide 12 Force elds How do forces act through space Charges surrounded by electric elds Vector eldsdirectional Fields and charges inseparable Fields act on other charges 0 Direction of elds motion of positive test charge in the eld Visualized with lines of force Same ideas apply to gravity and magnetism Electric eld lines point toward point toward negative charges Electric eld lines point away from positive charges 6 The force between 2 charged particles A is inversely proportional to the distance between them squared 7 2 spheres each have an excess of 10quot14 electrons and are separated by 10 m The magnitude of the repulsive force between them is Slide 15 Force Fields Charges surrounded by electric elds vector eldsdirectional Fields and charges inseparable Fields act on other charges 0 Direction of elds motion of positive test charge in the eld Visualized with lines of force Same ideas apply to gravity and magnetism Slide 16 Scalar eld associated with potential energy Unitsvolts V Related to work involved in positioning charges Potential difference important in producing forces and moving charges Analogous to moving masses in gravitational elds 8 The potential difference that is created by doing 100 joule of work in moving 100 coulomb of charge is de ned to be B 10 volt 10 Which of the following are misconceptions concerning electric current A The electrons move at nearly the speed of light through a wire Slide 19 Electrical Resistance Loss of electron current energy Two sources 0 Collisions with other electrons in current 0 Collisions with other charges in material Ohm s law See Ohm s aw ab RV or VR Reectrical resistance Vvolt current Unit Ampere for current R wave length 2 Slide 20 More on resistance Resistance factors 0 Type of material 0 Length Crosssectional area 0 Temperature Superconductors Negligible resistance at very low temperatures 6 Resistance in circuits Series connection 0 Total resistance is the sum of all the components 0 Current drops as more elements are added R tota R1R2R3 Series connection 1Rtota 1R1 1R2 1R3 Flip to getjust Rtotal o More than one current path available 0 Overall resistance drops as more elements are added 11 If a potential difference of 120 V is required to produce a current of 30 A in a wire the resistance of the wire is A 40 Q Slide 22 Electrical power and work Three circuit elements contribute to work Voltage source Electrical device Conducting wires 0 Maintain potential difference across device 0 Input wire at higher potential than output wire 0 Output wire ground for AC circuits 0 No potential difference no current bird on a wire 7 Electric Power 66 Electric power current potential difference P IV I current units ampere Vpotential difference volts Electric power 12 Electric power is B current times voltage Slide 24 Electric current Earlier electrostatics Charges more or less xed in place Now charge allowed to move 0 Electric current 0 Flow of charge 0 Reason for charge ow potential voltage differences 0 Electric circuits Structures designed to localize and utilize currents Slide 25 The electric circuit Structure Voltage source 0 Energy input Necessary for continuing ow Circuit elements 0 Energy used up as heat light work Current ow convention from high potential to low potential through the external circuit Waterpump analogy Slide 26 The nature of current Historically nature of quotelectrical uidquot unknown Current thought to be a ow of positive charge Reality more complicated depending on material Opposite correct in metal current electron ow Slide 27 Current mechanisms Liquids and gases 0 Both positive and negative charges move in opposite directions Metals Delocalized electrons free to move throughout metal quotelectron gasquot Drift velocity of electrons slow 0 Electric eld moves through at nearly light speed No eld electron motion random Electric eld propagates through metal at nearly light speed slow drift component added by electric eld Slide 28 More current details Current charge per unit time Units ampere amps A Direct current DC 0 Charges move in one direction 0 Electronic devices batteries solar cells Alternating current AC 0 Charge motion oscillatory No net current ow 9 The ow of charge is de ned as o D Current 8 Magnetic Poles and Fields Slide 30 Magnetism Earliest ideas 0 Associated with naturally occurring magnetic materials Iodestone magnetite Characterized by quotpolesquot quotnorth seekingquot and quotsouth seekingquot o Other magnetic materials iron cobalt nickel ferromagnetic Modern view Associated with magnetic elds Field lines go from north to south poles Slide 31 Magnetic poles and elds Magnetic elds and poles are inseparable Poles always come in Northsouth pairs Field lines go from North pole to south pole Like magnetic poles repel unlike poles attract Slide 32 Sources of magnetic elds Microscopic elds 0 lntrinsic spins of subatomic particles electrons protons o Orbital motions of electrons in atoms Macroscopic elds 0 Permanent magnets o Earth s magnetic eld Electric currents Electromagnets Slide 33 Permanent magnets Ferromagnetic materials Atomic magnetic moment Electronproton intrinsic moments 0 Electron orbital motion Clusters of atomic moments align in domains Not magnetizeddomains randomly oriented Magnetized domains aligned Slide 34 Earth s magnetic elds Originates deep beneath the surface from currents in the molten core Magnetic north pole south pole of earth s magnetic eld Magnetic declinationo set Direction of eld periodically reverses Deposits of magnetized material 0 Last reversal 780000 years ago Question 15 One theory as to the cause of Earth s magnetic eld is B the owing of liquid iron and nickel within the core as earth rotates Slide 36 Electric currents and magnetism Moving charges currents produce magnetic elds 37 Shape of eld determined by geometry of current 0 Straight wire 0 Current loops Solenoid Question 14 In 1820 Hans Oersted discovered that electrical currents produce magnetic elds when D he found that a wire carrying a current de ected the needle of a magnetic compass Slide 39 Electromagnets Structure Ferromagnetic core 0 Current carrying wire wrapped around core Field enhanced by the combination Can be turned ono Used in many applications meters switches speakers motors Slide 40 Electric meters Instrument for measuring current ammeter Uses magnetic eld produced by the current Magnetic eld and hence de ection proportional to current Modi ed can measure 0 Potential voltmeter Resistance ohmmeter Slide 41 Electromagnetic switches Relays Use low voltage control currents to switch larger high voltage currents ono Mercury switchthermostat Solenoid switches Moveable springloaded iron core responds to solenoid eld 0 Water valves auto starters VCR switches activation of bells and buzzers Slide 42 Telephones and loudspeakers coupling acoustic waves to electric currents Telephone 0 Sound vibrates carbon granules changing resistance 0 Changing resistance varies current Speaker Varying current changes eld of electromagnet moving permanent magnet Moving magnet vibrates spring attached to paper cone producing sound Slide 43 Electric Motors Convert electrical energy to mechanical energy Two working parts 0 Field magnetstationary Armature moveable electromagnet Armature rotates by interactions with eld magnet Commuter and brushes reverse current to maintain rotation Slide 44 Electromagnetic induction Causes Relative motion between magnetic elds and conductors Changing magnetic elds near conductors Effect Induced voltages and currents Induced voltage depends on Number of loops Strength of magnetic eld Rate of magnetic eld change Slide 45 Generators Structure Axle with main wire loops in a magnetic eld Axle turned mechanically to produce electrical energy AC generator quotalternating currentquot sign of current and voltage alternate DC generator quotdirect currentquot sign of current and voltage constant 9 Transformers More coils on secondarystep up transformers More coils on primarystep down Slide 46 Transformers Problems in power transmission 0 High currents large resistive losses 0 High voltages dangerous potential differences Solution transformers boostlower AC currents and voltages Basic relationships 0 Power inpower out 0 Number of coils to voltage equation 68 Question 16 Can you name everyday things that make life easier for us because of electromagnets E All of the above electric meters thermostats mechanical switches on VCRs and doorbells electric motors Slide 48 Circuit connections Alternating current 0 Practically all generated electricity Transmitted over high voltage lines and stepped down for use in homes and industry Direct current 0 Used in automobiles cell phones mp3 players laptops Moveable and portable applications 0 Main current source is chemical batteries Question 18 A transformer in which the number of turns in the primary coil is greater than the number of turns in the secondary coil A is called a step down transformer Question 19 In an ideal transformer the primary voltage is 120 V and the primary current is 20A If the output voltage is 1200 V the output current will be D 02 A Slide 51 Voltage sources in circuits Series circuit 0 Negative terminal of one cell connected to positive terminal of another cell 0 Total voltage is the sum of single cell voltages 0 Single current pathway Slide 52 Parallel circuit 0 All negative terminals connected all positive terminals connected Resultant voltage determined by the largest cell voltage 0 Makes greater electrical energy available Slide 53 Resistances in circuits Series connection 0 Total resistance is the sum of all components 0 Current drops as more elements are added Parallel connection 0 More than one current path available 0 Overall resistance drops as more elements are added 0 Total circuit current increases as more elements are added Slide 55 Household Circuits Combination series and parallel circuit 0 Light xtures in a room in parallel Appliances in parallel Same voltage available to each 0 Circuit breakers and fuses prevent overloads Slide 56 Household circuit safety Potential difference from two wires per device Energized oad carrier Grounded or neutral wire Threepronged plug 0 Provides another grounding wire Other devices polarized plugs groundfault interrupter GFI Chapter 6 Quiz Questions 1 The unit of electrical charge is called a B Coulomb 2 An electric current is C Flow of charge 3 Electrical power is measured in D Watts 4 Ohm s law states E That the current in a circuit increases if the potential difference decreases 5 NP 10 V120 Ns20 Vs 240 V Physics Chapter 7 Core Concept Light is electromagnetic radiation energy that interacts with matter Slide 2 Structure Regenerating cooscillation of electric and magnetic elds 0 Transverse waves 0 Electric magnetic and velocity vectors mutually perpendicular Electromagnetic spectrum Question 3 Which of the following has the highest energy ie highest frequency B Xray Slide 4 Sources of light Matter constantly emits and absorbs radiation 0 Emission mechanism Accelerated oscillating charges produce electromagnetic waves 0 Absorption mechanism Oscillating electromagnetic waves accelerate charges within matter 0 Different accelerations lead to different frequencies Luminous Producing light The sun vs the nonluminous moon Incandescent Glowing with visible light from high temperatures Examples ames incandescent light bulbs Question 1 Which of the following is not luminous C Moon Question 2 Which of the following is an incandescent light source D Candle Slide 7 Blackbody radiation Blackbody Ideal absorberemitter of light Radiation originates from oscillation of nearsurface charges 0 Increasing temperature Amount of radiation increases Peak in emission spectrum moves to higher spectrum 0 Spectrum of the sun see slide 7 for pictures Question 4 The majority of the the sun s radiant energy is in the form of B Visible light Question 5 our eyes are most sensitive to sunlight with a frequency that is B near the yellowgreen region of the visible spectrum Slide 10 Properties of light 2 models 0 Light ray model Particlelike view Photons travel in straight lines Applications 0 Mirrors 0 Prisms o Lenses 0 Wave model Traces motions of wave fronts Best explains o Interference o Diffraction o Polarization Question 6 light that interacts with matter can be D any combination of the above re ected absorbed transmitted Question 15 which of the following properties of light cannot be described by using the wave model of light D photoelectric effect Slide 13 Light interacts with matter 0 Interaction begins at surface and depends on Smoothness of surface Nature of the material Angle of incidence Possible interactions Absorption and transmission Re ection Refraction Slide 14 Diffuse Re ection Most common visibility mechanism 0 Each point re ects light in all directions Bundles of light from the object are seen by the eye 0 Colors result from selective wavelength re ectionabsorption Slide 15 Re ection Details Angles measured with respect to the quotsurface normalquot Line perpendicular to the surface 0 Law of re ection incident ray norm re ected ray qiqr 6 Image formation Slide 16 Image formation 0 Real image Can be viewed or displayed at its location Example movie image on a screen because all the lights are gathered on the screen 0 Virtual image Appears to come from a location where it is not directly visable Examples plane mirror convex mirror concave mirror 3 Refraction air to water incidence cannot go straight must bend speed of light is slower in waterglass refracted toward normal incident angel gt refraction angle water to air bend away from normal toward new material faster speed of light is refracted Refracted angle lt critical angle Critical angle re ected at 90 degrees Slide 17 Refraction Light crossing a boundary surface and changing direction 0 Reason change in light propagation speed Moving to a medium with a slower propagation speed 0 Light bends toward surface normal Moving to a medium with a faster propagation speed 0 Light bends away from the normal Mirages Critical angles Light refracted parallel to surface No light passes through surface quottotal internal re ectionquot Applications ber optics gemstone brilliance Question 9 What property of light do you have to keep in mind while looking at sh in a lake or stream B light bends when it hits the air to water interface The sh you spotted is not where you think it is Question 10 the incident angle of a light ray that travels from water to air and is refracted at 90 degrees is called the C Critical angle Slide 21 Refraction continues 0 Index of refractions A A measure of light speed Question 11 the ratio of speed of light in a vacuum to the speed of light in a medium D is called the index of refraction Question 12 the speed of light is 300x 10quot8 ms If the index of refraction of glass is 150 the speed of light in glass is A 200 x 10quot8 ms Slide 24 dispersion and colors 0 White light Mixture of colors in sunlight Separated with a prism o Dispersion Index of refraction varies with wavelength Different wavelengths refract at different angles Violet refracted most blue sky Red refracted least red sunsets Example rainbows Wavelengthfrequency related equation 73 Question 14 When white light is passed through a prism at the correct angle the colors of the rainbow are produced This dispersion of light is due to the fact that B Each color of light has its own index of refraction Question 16 The frequency of a photon of red light has a wave length of 680 nm is B 441 x 10 quot14 Hz Question 13 A ray of orange light has a frequency of 49 x 10quot14 Hz The corresponding wavelength of this light is D 612 nm Slide 28 Optics 0 The use of lenses to form images Concave lenses Diverging lenses Vision correctionin association with other lenses Convex lenses Converging lenses Most commonly used lens Magni ers cameras eyeglasses telescopes Slide 29 The human eye 0 Uses convex lens with muscularly controlled curvature to change focal distance Nearsightedness myopia images form in front of retina Correction lenses glasses contacts are used to move images onto retina Slide 31 The nature of light wavelike behavior Interference Young s 2 slit experiment 0 Interference patternseries of bright and dark zones 0 Explanationconstructive and destructive interference Slide 32 wavelike behavior polarization 0 Alignment of electromagnetic elds 0 Unpolarized light mixture of randomly oriented fields 0 Polarized light electric elds oscillating in one direction Slide 33 Polarization continued 0 Unpolarized light mixture of randomly oriented fields 0 Polarized light electric elds oscillating in one direction 0 2 lters passage depends on alignment Re ection polarization Question 17 why do polarized sunglasses reduce glare re ected light C The re ected light is polarized in the horizontal plane and the glasses are polarized in the vertical plane Slide 35 ParticleLike Behavior Quantization of energy 0 energy comes in discrete quanta used by Planck to explain blackbody radiation observations particles of lightphotons detected in digital cameras with CCDs chargecoupled devices equation 73 Slide 36 Photoelectric effect ejection of electrons from metal surfaces by photon impact 0 minimum photon energy frequency needed to overcome electron binding PE 0 addition photon energy goes into KE of ejected electron intensity of light related to number of photons not energy 0 application photocells Question 19 what is the photoelectric effect E all above describe the photoelectric effect electrons are emitted when speci c materials are exposed to light energy of a light wave occurs in discrete amounts of energy called quanta Einstein de ned the quanta as photons light is a stream of moving particles called photons Slide 38 Special Relativity concerned with events as observed from different points of view based upon Einstein s principles of consistent law principle constancy of speed principle shows that measurements of length time and mass are different moving reference frames the length of an object is shorter when moving moving clocks run more slowly moving objects have increased mass Question 20 when viewed from a stationary platform an object moving at speeds approaching the speed of light would according to the Special Theory of Relativity D Find that all of the above are true be shorter than when it was not moving have an increased mass nd that time has slowed down Slide 41 General Theory of Relativity Also called Einstein s geometric theory of gravity Gravitational interaction is the result of the interaction between mass and the geometry of space 4th dimensional quotspacetimequot structure
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