PHYS 1010 - Final Study Guide
PHYS 1010 - Final Study Guide PHYS 1010-01
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This 8 page Study Guide was uploaded by HaleyG on Monday April 25, 2016. The Study Guide belongs to PHYS 1010-01 at Tulane University taught by Timothy Schuler in Fall 2016. Since its upload, it has received 56 views. For similar materials see Great Ideas in Science & Tech in Physics 2 at Tulane University.
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Date Created: 04/25/16
PHYS 1010 Final Study Guide Waves (repeating motion) Transmitting energy using waves Transfer of energy without physically moving stuff from one point to another All waves have diffraction and interference (particles have neither) Diffraction: moving around an object in its path Interference: overlapping waves create new waves Mechanical waves: some type of physical medium transmits the waves Medium is not necessarily moving left and right, just up and down Electromagnetic waves: don't require a medium Magnetic and electric fields that drive each other Matter waves: waves behaving like particles Properties of waves Amplitude: height of wave Wavelength: distance between peaks of waves Period: time between each wave passing a certain point Frequency: how many waves go by per second (basically same as period) Velocity: wavelength x frequency Creating waves Transverse waves: amplitude is perpendicular to motion Longitudinal waves: amplitude is parallel to motion Interference Linear Superposition: overlapping/colliding waves create a resultant wave Constructive interference: add two waves with positive amplitudes together to get a bigger wave Waves are "in phase" with each other: travel together and overlap Speaker systems set up to create constructive interference (domed auditoriums, concert halls, etc.) Destructive interference: add two waves with opposite amplitudes, which cancel each other out Waves "out of phase": one has positive amplitude at the same point where the other has negative amplitude Noise cancelling headphones Resonance Two waves of the same amplitude/wavelength moving in opposite directions Adding the amplitudes at various times > standing wave pattern Standing wave: stationary waves Node: location where amplitude is minimum; nodes don't change location Antinode: location where amplitude is maximum Waves confined between two boundaries creates a standing wave pattern, produced at resonance Musical instruments create resonance/standing waves to build sound on top of to create more complex sounds Sound waves Longitudinal Amplitude is pressure Change in pressure > volume Speed of sound depends on material it travels through Speakers Magnet w/ coil of wire around it, electric current switching direction creates vibration, which creates sound waves/pressure (x2: one input and one output) The Doppler Effect Change in frequency as a soundemitting object moves with respect to an observer As waves are emitted they are catching up to the wave in front of them > smaller wavelengths in front of source, bigger waves behind the source > higher frequency (higher pitch) Source of sound travelling at speed of sound > overlapping waves with huge amplitude ("sonic boom") and change in pressure ("shock waves") Thunder is a sonic boom: lightning heats air, which creates expansion and a pressure/sound wave Measuring weather Satellites give off waves, which travel until they hit something dense that reflects it (like a cloud); reflected waves have a higher frequency the faster the clouds are moving toward them/lower frequency if clouds are moving away Big bang theory Hubble noticed the farther away a star is from earth, the redder it looks (lower frequency because stars are moving away) Everything is moving away from everything else in the universe Means that everything in the universe had to start in one place Electromagnetic Spectrum Light behaves as a traveling wave of electric and magnetic fields Different frequencies are different colors, most of which are invisible to humans Spectrum has no upper or lower bound, and is continuous All electromagnetic waves in a vacuum travel at the same speed Spectrum: Long waves > radio waves > infrared > visible light spectrum > ultraviolet > xrays > gamma rays Everything below visible light spectrum can't cause chemical change Reflection and Refraction Reflection: light bounces off the surface in a slightly different direction Refraction: light moves through the surface, and speed changes based on the densities of the new medium; the direction then changes to compensate for the new speed Light travels more slowly in denser material Light has to always be the fastest thing in the room, and it takes the fastest path, not the shortest path If light has to travel through air and water, it will spend longer in the air and shorter in the water because it moves faster through air Chromatic dispersion: light spreads out by color when moving through glass/water, because the amount light bends depends on the frequency of light and the density of the mediums (rainbows) Higher frequencies bend more than lower frequencies Reason why the sky is blue: sun is white light, which refracts when it hits the atmosphere. Light from sun travels at an angle, which then refracts at us. We see blue because blue bends more than any other color. The sun is red at sunset because it has to travel through a lot more atmosphere to get to us. The red light gets through because it doesn't have to bend very much. Polarization Polarization: the direction in which the electric field is oscillating Sun's light/light from most common sources is unpolarized because it comes from all different directions Using a filter that blocks one specific direction of polarization can polarize unpolarized light Filters in both directions block all light Polarized sunglasses prevent glare Diffraction Occurs when waves encounter a barrier that has a small opening After the wave passes through, it spreads out Lower frequencies bend more than high frequencies, so putting a barrier up to block sound will result in us only hearing low pitches Diffraction causing interference Thomas Young's Interference experiment Shining light through two openings creates overlap of waves, creates bright spots and dark spots Proves light is a wave because it interferes and diffracts Problem with light as a wave Shining light onto a piece of metal makes electrons pop off the metal, but the energy and speed of those electrons did not depend on the intensity of the light, just the color. But, the brighter light is, the more it should be moving the electrons Einstein said we can explain this experiment if light is a particle Light is a wave AND a particle Wave/particle duality Perform Interference Experiment and see particles behave like waves Issues with light Light moves at a constant speed, always Light behaves like a wave sometimes and like a particle sometimes Relativity: trying to describe when/where something happened Reference frames: different perspectives of viewing an event Spacetime coordinates: 4 assigned values: N/S, E/W, up/down (space), and time Different depending on reference frame Idea that stationary viewer is more correct about direction of movement But, there is no "correct" reference frame Special relativity Because of reference frames, there's no such thing as simultaneous events (depends on motion of observer) The "special theory of relativity" Postulate 1: laws of physics are the same in any inertial (non accelerating) reference frame Postulate 2: speed of light in a vacuum has the same value in all directions and all inertial reference frames Relativity of time Light moves the same speed, but shorter/farther distance and longer/shorter time depending on different reference frames > Time is not absolute/different depending on reference frames If you're moving, time slows down Grows exponentially as speed increases When travelling at the speed of light, time is infinite Therefore, we can never reach the speed of light (it would take an infinite amount of time) Relativity of length Length of moving objects is relative As an object moves, length contracts Moving at the speed of light > length is 0 Relativity of momentum Mass increases the faster you go Moving at the speed of light: infinite mass requires infinite force Relativity of energy Mass and energy are the same thing (mass is the physical representation of potential energy) Manhattan Project: development project of nuclear weapons Mass > energy Trinity Test: detonation of plutonium bomb Proved Einstein’s theory of relativity Radiation Mass turning into energy in unstable atoms Nuclear fission: breaking big things apart; how we generate nuclear power Leaves nuclear waste Nuclear fusion: taking small atoms and ramming them together; give off energy because they lose a little mass No waste, no toxicity Takes too much energy (takes more energy to complete process than we get out of it) Light turning into an electron Turns into two particles > electron and positron (electron with + charge) Electrons are matter Positrons are antimatter Electrons smashing into positrons destroy each other and turn into light General theory of relativity Covers accelerating and nonaccelerating reference frames You can always tell if you are accelerating by dropping an object and watching it move, but we can't distinguish between an accelerating reference frame and gravity Airplanes travel in curved paths because they take the shortest route possible. They fly closer to the North or South Pole and then back down because the earth is smaller further from the equator Light can travel in a curved path because space itself is curved; on a curved surface, the fastest path is curved So, gravity exists because mass curves space Mass creates an indentation in spacetime, which explains the attractive nature of gravity The more massive an object is, the more it will curve space Black holes Forces on stars: gravity that pulls hydrogen atoms in causing fusion, which creates energy; that energy pushes everything outward (balanced with gravity) Hydrogen runs out and moves on to helium and so on, which creates even more energy and the star expands outward When stars start fusing iron, iron doesn't create any energy so the explosive force goes away and gravity is all that's left Crushes atoms to a tiny mass, which stretches spacetime a LOT Nothing can escape from a black hole We see black holes because we see the light going into them Bending/warping space Alternative to travelling at the speed of light "Wormholes" describe a mass large enough to curve space Newton says that light isn't affected by gravity because light doesn't have mass; Einstein says light will be affected by gravity because light curves Gravitational lensing: light bending because of gravity Proof of relativity The Creation of the Universe The Big Bang: at the beginning of time, the universe existed at one point, which exploded, sending the universe expanding in every direction Evidence: the universe is still expanding The universe is 14 billion years old Cosmic background radiation: noise/energy in empty space leftover from the big bang Less energy where there is a lot of mass (galaxies) because energy turned into mass Nothing existed before the big bang because time didn't exist until the big bang Big Bang > particles combine to form bigger particles in the first three minutes Because light from super far stars are still traveling toward us, we can look at things really far away and be looking back in time The Death of the Universe Possibilities: 1. There's not enough mass for gravity to overcome the force of the Big Bang > the universe will continue to expand forever The further things go, the faster they move 2. There's lots of mass and gravity will overcome the force of the Big Bang > the universe will slow down and reverse, with the end in a "big crunch" 3. The force of gravity and the energy from the Big Bang are perfectly matched > expansion slows down and approaches zero, and then we don't know what happens next Evidence suggests the universe is close to this possibility There's a lot of mass in our galaxy that we can't measure; we know it's there because otherwise our galaxy wouldn't hold together "Dark matter"; does not interact with light We don't know how much there is The expansion of the universe is increasing/accelerating, which does not make sense because gravity should be slowing it down "Dark energy" Atoms Robert Brown saw that pollen grains and water were moving under a microscope JJ Thompson discovered a cathoderay tube: wireless transmission, sending light that bent near magnets (electrons) from one place to another Discovery of electron Millikan was able to measure the charge/mass of an electron Rutherford realized atoms have a positively charged nucleus Discovery of proton Quarks Types: UP (+2/3e), DOWN (1/3e) STRANGE, CHARMED, TOP, BOTTOM (no longer existent) Protons: 2 UP and 1 DOWN Neutrons: 1 UP and 2 DOWN Different colors: red, green blue Quarks adding up to atoms must add to white (red + green + blue), otherwise they won't stick together The Standard Model of Particles Equation that combines all particles discovered and theorized that make up everything in the universe String Theory: everything in the universe is based on vibrations in energy, which cause matter and charge to exist Photoelectric effect: light behaving like a particle Light as a wave > interference pattern in dual slit light experiment is a probability wave The motion of particles is a probability The probability is described by a wave The bigger things are, the smaller their wavelengths are; so, for large things like humans, motion is still a probability but just an immeasurably small one Heisenberg uncertainty principle: the more we know about the position of a particle, the less we know about its momentum (and vice versa) Before we measure a particle, it doesn't have a position, just a probability of a position; by measuring it, we force it to choose properties Energytime uncertainty Photons borrow energy from the universe and turn into an electron or a positron They can only borrow the energy temporarily Positron = an electron moving backward in time Antimatter is matter moving backward in time Indistinguishability: we can't tell two electrons apart EPR Paradox: a photon turns into an electron and a positron (energy > mass) one goes to the right and one goes to the left; both have an equal chance of being a positron or an electron, but we don't know which, because we haven't measured them Even though these particles are far away, measuring one immediately describes the properties of the other Strange connection between particles If this is true, information travels faster than the speed of light QuantumXeno Paradox Unstable situation like balancing a ball on a sharp point Describing the situation as a factor of time and probability Beginning of time 100% As time goes on, probability goes down Not watching it for a brief amount of time measures it > probability goes away/starts over By continually watching it, it is a stable situation Interpretations of energytime uncertainty Hidden variables interpretation: there must be more information that we don't know Copenhagen interpretation: assuming that measuring something collapses a wave function is problematic for some reason we don't know Many worlds interpretation: measuring something makes it choose both possibilities, which creates an infinite number of universes
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