USC Geology 130 – Flashcards
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What is science?
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science is a way of obtaining knowledge about the physical world
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Ways of knowing
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1. sensory experience: not always reliable, not always complete, senses are narrow 2. consensus of opinions with others: majority vote does not guarantee true 3. expert opinion: more experienced, but still can be wrong 4. logic: room to extend knowledge, but also room for errors (ex. syllogisms)
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Scientific method
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a. identification and definition of a problem b. formulation of a hypothesis c. projection of consequences d. testing of predicted consequences **not always in this order: often experimental observations cause problems that stimulate new theory
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Where and why the scientific method fails
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a. hypothesis stage--no ideas/lack of imagination b. computing stage--mathematics too difficult/lack of credentials c. experimental state--can't perform key experiments/can't validate
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Criteria for "good theory"
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accurately describes a large class of observations on the basis of a model that contains only a few arbitrary elements a. must make definite predictions about the results of future experiments b. must be falsifiable (ex. one cannot predict creationism)
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How do you know when your theory is correct?
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a. recognize the truth by its beauty and simplicity (ex. Watson and Crick-double helix DNA structure, plate tectonics) b. more comes out than goes in c. if it is not revealed immediately that it is wrong, and it is simpler than before, then it is right d. **you can never prove a theory true, only that it is not false** (not absolute)
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What if two theories predict identical results?
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a. there is no scientific way to distinguish them 2. they may give different insights into a problem 3. choose the simpler (ex. Occam's Razor-cut out unneeded or unobservable parameters)
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How to determine a subject as suitable for scientific research
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a. if hypothesis is testable/can be proved through science, it is suitable (ex. ESP, crystal power, animal behavior, astrology, acupuncture) b. if hypothesis is not testable/unclear/cannot be disproved, it is unsuitable (ex. flying saucers, creationism)
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Relation of science to philosophy
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a. philosophy questions the existence of the external world b. science assumes it exists and can be understood
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Relation of science to social science
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a. social science has a lack of precise definitions b. poor control on variables
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Relation of science to technology
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**Goal, Product, Reward** technology: problem solving, useable objects, money science: understanding, ideas, esteem
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Maturing of a science
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a. description (organizing, categorizing) b. competing hypotheses c. general acceptance of a paradigm (accepted model, pattern, way of thinking) d. scientific revolution: replacement of one paradigm by another; driven by observation; driven by simpler/more comprehensive theory
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Thales Leap
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-beginning of science -600 BC Thales of Miletos -broke with myth -asked "what is the world made of" -answered "water" -most of Greek science is wrong, but the process is important
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Aristotle's view: the nature of matter
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-Aristotle's view (350 BC) endured until the Renaissance (14th-17th centuries) -earth matter composed of fire, water, air, and earth -all matter can be transmuted from one form to another -considered properties of matter (ex. combustible, meltable, etc.) -cataloged variety of substances
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Atomists
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(435 BC) believed the Universe to be composed of infinite, invisible particles (atoms); all have solidity, weight, and different size/shape
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Zeno of Elea
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(445 BC) argued against discrete particles and a void; believed time/space were continuous quantities, not inherently discrete
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Aristotle's view: motion on earth
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-related to the nature of matter -classified all motion on Earth into 4 types: natural motion (inanimate objects), forced or violent motion, animate motion (living things), celestial motion (Aether has inherent circular motion/sun, moon, stars, plants made of aether) -all inanimates move naturally up/down depending on proportion of 4 elements -natural state = stationary (a moving object will eventually rest) -fault: objects fall at speed proportional to weight
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Aristotle's view: motion of the stars
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-stars (in heavens) move naturally in circles, are immortal, and are unchanging -stars are made of aether (an immutable substance unlike 4 elements) -natural movement of aether is up/down
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Greeks and time
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-Greeks knew of existence of time, but didn't relate to human/natural philosophy -Heraclitus: everything is subject to change (500 BC) -Parmenides: nothing changes (480 BC) -Empedocles: 4 elements exist and produce change thru interaction
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Starting point
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-flat Earth -Intuitively correct -proper place for man (at center) -Earth is spherical Aristotle (340 BC) -evidence through shape of lunar eclipse (circular) -North star changes position in sky as you travel N or S -size of Earth, Aswan v. Alexandria = 15% too large -current value: R=6378km -measured with pole in different countries
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Aristotle's view: planetary revolution
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-(340 BC) Aristotle believed Earth was stationary; sun/moon/planets/stars revolve around Earth in circular orbits -circular motion = perfect like nature -earth at center = most important
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Does culture/language affect science?
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yes, but observation and how we describe things prevails in end
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Hercleidas
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(370 BC) Earth rotates on axis (no overwhelming evidence, modern science not developed, pure reason)
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Aristarchus
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(3rd Century BC) Earth moves around sun (no overwhelming evidence, modern science not developed, pure reason)
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Problem with geocentric view
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(427-347 BC) Plato questioned pattern of motion of planets
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Claudius Ptolemy
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(85-165 BC) perfected circles with moving centers on larger circles
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Nicolaus Copernicus
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(1473-1543) Polish priest -sun is stationary and at center of universe -at odds with Aristotle mechanics -Earth and planets revolve around circular orbits
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Tycho Brahe
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(1546-1601) -did not believe Copernicus -made accurate map of planetary motion relative to fixed stars -still used today
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Johannes Kepler
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(1571-1630) -worked for Brahe -poor observer, but liked mathematical puzzles -found simpler laws describing Brahe's data aka Kepler's Laws 1. elliptical orbits = sun at one focus (pencil experiment) 2. radius vector sweeps out equal areas in equal times (longer = slower, shorter = faster) 3. R3/T2 = constant (R= radius of planet, T = time); Earth's orbit takes 365 days
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Galileo Galilei
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(1609) -used telescope to observe moons of Jupiter -everything doesn't orbit Earth -agrees with Kepler's laws -discovered Inertia -bodies in motion remain in motion at constant velocity -inclined plane experiment -natural state of motion = constant velocity -constant velocity = constant speed in straight line -"frames of reference" like a cabin in a moving ship
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Aristotle's paradigm for motion
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a. the natural state of an object is at rest b. it takes force to put an object in motion and **keep** it in motion c. there are three types of motion: natural (up/down/circular), forced, and animate
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Isaac Newton
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(1642) -born the year Galileo died -(1) introduced new paradigm for motion -(2) universal law of gravitation -(3) used (1) and (2) to explain orbital motion: centripetal force provided by gravity, -(1687) published greatest work Mathematical Principles of Natural Philosophy: mathematical description of motion -**significant because people still believed in geocentric view** -**people rethought because planets don't orbit in circular motion around earth
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Orbit plane
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-relates to astrology -main planets share a plane
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Newton's Laws of Motion
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1. a body traveling in a straight line at constant speed continues unless acted on by an external force (Galileo's inertia = momentum = mass*velocity) 2. a force is defined by how it changes momentum (force = change in (mv)/change in time) aka mass*acceleration 3. for every action, there is an equal and opposite reaction **explained Kepler's laws with simple mechanics**
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Newton's Universal Law of Gravitation
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-sorted out gravity -Newton's 3rd law
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Weighing the earth
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-Cavendish -hung spider from roof, measured force to spin it -dropping rock on earth experiment -figured out all variables until mass was left
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Kepler's laws from Newton's laws
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1. elliptical orbits = inverse square law force 2. equal areas in equal times = conservation of angular momentum 3. t2/R3 = constant = inverse square law force
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Newton and free will
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if you know the positions and velocities of all the particles in the universe at a given time, you can know the past and predict the future; we have a "mechanical universe" and therefore have no free will
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Sir William Herschel
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(1738-1822) discovered Uranus (1781) thru irregularities in the orbits of other planets using Newtonian mechanics (aka objects with masses = able to predict motion/behavior) used parallax to measure distance to nearest stars
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Parallax
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triangular pattern made by two rays (ex. two eyes connecting to create one 3D vision) allowing one depth perception to discover Uranus: measured distance at two points (one in June and one in December) to estimate the path to planet can only be accurate at a certain distance away (10^18 meters, therefore, it can only be used to measure nearest stars as closest is 10^17) confirmed the milky way is a galaxy (the galaxy we live in, 100,000 light years wide, billions of stars) the closer the star = the more they travel
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Andromeda Galaxy
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nearest, most similar galaxy to ours, 2.5 million light years away center of galaxy = black hole (huge amount of mass have collapsed into a single point spiral galaxy
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Pleiades
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star clusters, known as the seven sisters blue halos around them blue stars are hotter than red stars
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Solar system
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Sun and orbiting planets; has to be influenced by the gravitational attraction of the sun
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Light year
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the distance light can travel within a year 1 light year = 9 * 10^15 m/light year
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Edwin Hubble
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(1889-1853) ours in not the only galaxy (1920) way to measure distances to other galaxies = color-intensity scale + inverse square law of light
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Inverse Square Law for Light
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F = force W = work, measure of energy (force*distance aka needs to move) P = power, measure of luminosity (measured in Watts = J/sec *more J = brighter*) I = intensity (Watt/m^2) a star (ex. the sun) puts out power like a light bulb a telescope measures intensity **if you know distance to star (r) from parallax, you can find P** **further we are from star = the more the energy will change blue = high energy** yellow-->red = low energy (Earth lives around yellow aka the sun) white = very hot, but low in power/luminosity x-axis = color of star (Temp) y-axis = luminosity (Watts) located in milky way
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Color-Power Relationship
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black body radiation curve: -as a body becomes hotter, it radiates more electromagnetic energy -the peak frequency increases with increasing temperature -aside on waves and the electromagnetic spectrum -the more energy = the closer to blue the color will be -relationship between temperature and peak of curve ex. stoves start red and slower travel from yellow to blue
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Distance from Color
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for stars too distant to use parallax 1. Use H-R diagram to find P from its color (spectral peak) --Watts = Joules/sec 2. Measure the observed intensity I using telescope 3. Use the equation P to find the distance to r (radius to star)
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How big is the Universe
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Cannot be finite and static = would collapse due to gravitational attraction
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Black-body radiation curve
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-(y distance) amplitude = measured from leveled wave to peak -(x distance) wavelength (Lambda) = peak to peak or crest to crest period (T) = time between peaks (seconds/cycle) frequency = 1/period (T) (cycles/second) velocity (fixed) = wavelength (Lambda) /period (T) = Frequency*wavelength Frequency and wavelength = inverse relationship peak = determined by temp
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Electromagnetic spectrum
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electromagnetic waves = frequency is how often the waves fluctuate between waves need to start at an equilibrium and then be disturbed to produce waves longest wavelength = radio waves (size of field/house) microwaves = size of baseball and smaller intro-red = stove top heat violet --> ultraviolet = what sun produces (cannot see, though insects can)
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Red Shift and the Expanding Universe
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Light from the Sun has a "dark line spectrum" or "Fraunhofer lines" Light from stars also have a dark line spectrum These lines are caused by absorption of specific frequencies in the stars "atmosphere" The frequencies are characteristic of the atoms in the atmosphere Doppler Shift: ex. race track, closer car is to you, high sound/frequency --Movement toward you = blueshift (shorter wavelength) --Movement away from you = redshift (long wavelength) --further the star = lower the frequency
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Expansion
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The redshift is proportional to the distance of the star The faster it's moving, the further away the star is = expanding
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Quasars
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Penzias and Wilson (1963) Far and really bright = enormous amount of power Microwave background radiation = noise is flash of big bang (40 billion years ago)
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What is light?
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Two answers historically: 1) a stream of particles (Newton) 2) waves (Huygens)
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How does light behave?
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1) reflection 2) refraction 3) dispersion 4) diffraction
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Reflection (light)
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Angle of incidence = Angle of reflection Particles (Newton) and waves (Huygens) both explain reflection Reflection of waves: --wavefront: eddies --rays: perpendicular to wavefront
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Refraction (light)
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Incident ray = initial light ray Angle of incidence = part of ray that will reflect Refracted ray = bent ray through medium Angle of refraction = angle ray is bent Particle explanation: Light speeds up when it goes from air to water Wave explanation: Light slows down when it goes from air to water
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Dispersion
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White light is composed of a mixture of the other colors The velocity of a wave depends on its wavelength Waves if velocity in glass is less than that in air Red = fastest, bend the least ~rainbow order~ Violet = slowest, bent the most
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Diffraction
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Light will bend when traveling through two slits Huygen's Waveletts: waveletts will add up to create a bending wave around aperture Must be waves (particles don't bend around corners)
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Measuring the speed of light
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1) Galileo attempted to time speed, but it was too instantaneous 2) Roemer and Galileo Period of IO would reach earth: 140,000 miles/sec 3) Modern value = 186,000 miles/sec
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Light is Electromagnetic Radiation
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James Clerk Maxwell (1831-1873) What is a field?: the value of something everywhere in space (F = qE) Electric field between parallel metal plates (E = V/d)
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The Magnetic Field
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Defined by the force of a **moving** charge Changing magnetic field = electric field Changing electric field = magnetic field
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How to generate an electromagnetic field
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Static charges an electric field Moving charges generate a magnetic field (and an electric field) Accelerating charges generate electromagnetic waves -higher acceleration = higher frequency -beam of electrons coming in and hitting a metal plate -ex. dentist x-ray
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What is waving
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Collapsing electric field produces a magnetic field collapsing magnetic field produces an electric field Electromagnetic waves require no medium They propagate at fixed speed in a vacuum Fixed speed is relative to nothing, no fixed frame of reference -creating "Ether" -speed of light is independent of the velocity of the source or of the receiver -everyone in an "inertial frame of reference" measures the same speed of light
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What we know about light
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1) light has a high velocity 2) light has a very short wavelength --wavelength = color --nm = nanometers = 10^9 meters 3) light has a very high frequency 4) the velocity of light in any matter is always less than that in a vacuum --index of refraction = speed of light in vac/speed of light in material 5) the velocity of light in any matter depends on its color (dispersion)
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Snell's Law for Refraction
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sin(0)/v1 = sin2(0)/v2 larger angle/larger vel. = smaller angle/smaller veloc. incident ray ; refracted ray reflection angles = the same
