Physics Exam 2 (2025 Version) Tested Questions with Accurate Answers.

Physics Exam 2 (2025 Version) Tested Questions with Accurate Answers. What evidence existed to suggest that there was an important physical quantity that depends on the square of the velocity? Experiments involving dropping balls into plastic mediums showed the depth of penetration was much better predicted by the second power of velocity than the first as Newton said, redefining kinetic energy What causes momentum to change? A force acting over time How is work different from change in momentum? Work is the product of force and distance traveled; momentum is the product of mass and velocity Why did a ship's crew lose weigh in cooler weather? The crew's body needed more energy to heat themselves causing them to lose weight on the same rations What three kinds of energy do we often see? Kinetic, potential and thermal energy What is the work-energy theorem? What quantities does it relate? The work energy theorem says that net work on an object causes a change in the kinetic energy of an object and related net work and kinetic energy Under what circumstances is positive work done? Negative work? Zero work. Work is positive when the object is moving faster at the end of the interval and negative when the object slows down during the interval; when it is not moving work its zero Why is the wheel such a great invention in terms of work and energy? With the wheel a horizontal force far less than the weight will keep the load in motion at horizontal speed What two kinds of motion involve kinetic energy? Force parallel to the distance and force anti-parallel to the distance What is the origin of the expression "speed kills". Kinetic energy depends on the square of the velocity so when the speed doubles the kinetic energy associated with risk quadruples What discovery about energy brought about the industrial revolution? Learning to transform thermal energy in steam into waste heat and useful work Why did the mining of coal become so important? What problem was encountered in the mining of coal? Coal was needed to smelt iron ore into steel. As coal miners dug deeper the problem of water leaking into the mines hindered efforts What is potential energy? Why is it defined only in terms of its change? An object has more potential to do work based on its position and because of this is can only be defined in terms of change In what sense is hydroelectric energy actually converted solar energy? Hydroelectric power plants operate by harnessing the potential energy of water at higher elevations. After all the sun's light evaporates water so it can rain at the water source for the plant What great contribution to society was brought about by Nicolai Tesla? Alternating current (AC); x-rays (first to discover, didn't get credit thought); radio; wireless transmission What happens to the gravitational potential energy of an object as it moves uphill? The work done is negative and the change in gravitational energy equals mgh Under what circumstances is mechanical energy conserved? When there is no (dissipative force such as) friction Under what circumstances is total energy conserved? Total energy is the sum of mechanical and thermal energy and is always conserved over an extended period of time How can points of equilibrium be located on a plot of position vs potential energy? These are the changes in direction at the peaks or valleys What makes points of stable equilibrium stable? How can stable equilibrium points be located on a graph of the potential energy function? What makes unstable equilibrium points unstable? How can they be located on the graph of a potential energy function? A point is in unstable equilibrium if any movement would lessen potential energy and increase kinetic energy so it moves way from the point with increasing speed Where do we see simple harmonic motion in nature? Any potential energy function that has a minimum will display motion very close to simple harmonic about its minimum such as atoms in diatomic molecules like oxygen What did Planck figure out about allowed energy values in simple harmonic motion? He figured out that the details of radiation emitted by a hot surface could only be explained by energy levels separated by equal amounts What is binding energy? Binding energy is simply negative of total energy; such as if a skater falls in a well it's excessive energy would need to get out If we define potential energy to be zero far from an interacting body, what determines the difference between bound and unbound states? Total mechanical energy of zero is the dividing line between bound and unbound states; negative energies are bound and positive energies are free or unbound Under what circumstances can useful energy be liberated? When there is an increase in binding then useful energy can be liberated Where did the potential energy in uranium come from? The energy came from energy stored as nuclear potential during the collapse of a heavy star long before the earth was formed How does the sun come to liberate so much energy? The sun liberates so much energy by fusing hydrogen into helium with a very strong nuclear force tightly binding the helium nucleus What is escape velocity from a planet? How do it depend on mass? As velocity gets larger and larger a particular value of the velocity will make the total energy zero. Since objects with this energy or greater can escape the gravitational well this is called escape velocity. The escape velocity is independent of the object's mass. Why did James Joule take a long thermometer to a waterfall? What did he expect to measure? Why did the effort fail? He was attempting to understand the nature of heat; he expected that the water at the bottom would be 1 degree warmer than at the top. The waterfall was too sporadic and as it fell from the top some water changed to vapor which also decreased heat What did Joule show in the lab? Why did the experiment in the lab succeed while the waterfall experiment failed? As water was stirred by falling weights it gained heat energy; the water was contained in an insulated container rather than outside which is why it succeeded in the lab What evidence existed so suggest that heat was a material substance? When a pile of wood was burned by fire, there were only ashes so heat must have had substance to account for the loss of matter What experiment did Benjamin Thompson conduct at the cannon factory? What did it prove? He attempted to drill cannon with a very dull bit; it proved heat was being released as long as the drilling was occurring even though there was no metal was cut; it disproved the notion that heat was present in the metal as a material substance What is the first law of thermodynamics? Energy cannot be created nor destroyed applied to heat What created the need for pumping water? The desire for iron, including the mining of coal Why does the steam engine create waste heat? What great improvement did James Watt make in the steam engine? The pressure must somehow be reduced to avoid having to do work to return to the piston. He was able to condense the exhaust steam into a liquid form with a separate condenser that returned to the boiler to be used again; this saved field by not requiring the rewarding of the piston and cylinder How did Carnot figure out the maximum possible efficiency of a steam engine? He used a model that was based on the water wheel; maximum efficiency was only possible by using only reversible processes What determines the maximum efficiency of an engine? The numerical value is determined by the 2 temperatures involved: the high temp of the steam and the temp of the cooling water Why are coal-fired electric plants often located on rivers? Because the cool river water helps in the temperature quotient Why are more efficient steam engines expensive to build? Higher temp steam would improve the theoretical efficient but higher temps means higher pressure which in turn means a higher cost to build the engine What determines the amount of power that can be extracted from a waterfall? The flow rate and the height of the falls What unit did Joule use to describe the power of his steam engines? Horsepower How does Duke Energy's Bad Creek Project make nuclear power profitable? They store energy produced from the nuclear reactor at night when it is not needed on the power grid. They store energy by pumping the water uphill to an elevated lake. When the max power is needed the energy stored as potential energy in the elevated pond is used to meet the peak demand How does a refrigerator work? How is it similar and different from a heat engine? Refrigerators move heat energy from a cooler place to a warmer one through the second law of thermodynamics meaning that a refrigerator is basically a heat engine running backward. They specifically use refrigerant which absorbs heat as it changes from a liquid to a gas cooling through evaporation An ice plant was built near Austin Texas in the early 1880's. How could such a plant operate without electricity? The plant used energy from a waterfall nearby to drive a compressor with heat energy removed from the freezer compartment and dumped the hot air through the falling water's work What are the major energy sources available today? What are the advantages of each? What are the problems? Coal - it has a low price and is abundant, but the mining of coal disrupts large tracts of land and it pollutes the air by releasing CO2; natural gas - its abundant and has a smaller carbon footprint, but the fracking of the gas pumps chemical into the earth which could be dangerous What is the challenge posed by the evolution of solar cells? The greatest challenge will be our ability to store the large amount of energy that will become available from cells on private homes. Right now they are still expensive and inefficient Apart from the changing of energy into matter, total energy is always conserved. If energy is always conserved, why do we keep burning so much fuel? Much of the energy is converted into waste heat as well as useful work What role did fuel cells play in the mission to the moon? Why was this such an important role? Fuel cells convert hydrogen into electricity and water which was useful in the Apollo Space Program as the hydrogen could produce both electricity and drinking water which saved weight which was imperative to space travel What is cogeneration? Why is it impractical in most of the US at present? The generation of electric power by the burning of fossil fuels produces heat that is useless to run a steam engine, but this waste heat can be used to heat and cool houses that are closer to the generating pointCoal fired plants produce nasty dust and smoke so people live far away. About 1/3 of the electric power generated in the US is lost in transmission Why are trains the most efficient form of transportation? The wheels are rigid so they roll with little friction; cars are closely spaced so air friction is far less for trains than individual tracks; trains typically have the right of way What is the advantage of hybrid cars? Hybrid cars can brake electromagnetically, using electro-magnetic force to both stop the car and charge the battery. So energy of motion can be converted into electric energy and then reused to get the vehicle in motion when the light turns green Where does most of the energy consumed in walking go? With the starting and stopping of the feet What is the greenhouse effect? What does it have to do with CO2? The effect created when energy is trapped inside the atmosphere; the process by which radiation from a planet's atmosphere warms the planet's surface to a temp above what it would be without its atmosphere. CO2 creates a layer in the earth's atmosphere and contributes to the greenhouse effect Why is natural gas better for the environment than coal? It is less harmful to the environment because it doesn't release as much CO2 How is it possible that more than 100% of the energy from sunlight reaches the earth's surface? Because much of the IR radiation leaving the surface of the earth is reflected backwards and this reflected IR is 80% of the sun's incident radiation What evidence suggests that humans are causing global climate change? CO2 levels and average annual temp have increased steadily over the last few decades What evidence exists to suggest that higher energy costs would produce greater energy efficiency? When energy costs went up in 1974 there was a dramatic increase in energy cost due to politics in the middle east which led to a dramatic increase in energy efficiency When did we enter the "petroleum age"? Where does much of our modern energy use go? 1950; transportation consumes a tremendous amount of this new form of transportation fuel What are the problems with hydrogen as a fuel? What advantages does it offer? Hydrogen is not found in nature. It can be used as an energy source once made, but its manufacture requires energy. It also doesn't easily liquefy for storage. It produces no carbon dioxide When was matter first considered to be composed of fundamental modules? Who brought forward this idea? Democritus and Leucippus were pondering what the universe was made of and after considering matter could either be divided a finite number of times or indefinitely; they picked the former as they could not cope with infinity What were the properties of the atoms imagined by the ancient Greeks? a. Matter is composed of atoms separated by empty space through which atoms move b. atoms are solid, homogeneous, invisible, unchangeable c. all changes in matter result from changes in grouping of atoms d. there are different kinds of atoms and they differ in size and shape e. the properties of matter reflect the properties of the atoms the matter contains What problem did Boyle see with Aristotle's four element view of chemistry. Boyle noted that no substances could be made from the four elements and that none of the four elements could be made from decomposing compound materials. Elements are those things that cannot be further like hydrogen Who brought back the idea of atoms? John Dalton What properties did Dalton expect atoms to display? Indivisible and indestructible (matter is made up of atoms that are indivisible and indestructible); identical (all atoms of an element are identical); different weights and chemical properties; combine to form compounds (atoms of different elements combine in simple whole numbers to form compounds) What errors were present in Dalton's assumptions about atoms? Assumptions 2 (atoms of elements are identical) and 3 (atoms of different elements have different weights and different chemical properties) aren't quite correct as a chemical is mostly determined by its protons so atoms with the same number of protons but different neutrons have nearly identical chemical properties. Therefore two different isotopes can exist that have the same atomic number and differing masses and isotopes of different elements can have almost the same weight What did Gay-Lusac discover about the volumes of gasses involved in chemical reactions? He found that reaction between gasses give simple numerical ratios for the volumes involved, like hydrogen and oxygen's 2:1 ratio in water What did Avagadro figure out about different gasses? Realized that simple ratios and assumptions imply that equal volumes of different gasses contained equal numbers of particles, and this is true as long as the samples share a common temp. What was confusing about hydrogen, nitrogen, and oxygen? These gasses are diatomic so they are not atomic in their gas state so Dalton thought it must be a combination of two atoms, like water being one H bound to one O atom What property did Dalton expect for each chemical element? He recognized that each element could be characterized by a relative weight What led to the defining of Avagadro's constant as we do? Avagadro recognized that equal volumes at equal temp and pressure contained equal numbers of particles which allowed for a constant to be created. This let a single number describe both How do we measure temperature? What calibration points have been used? Temp is measured by mercury expanding and contraction gin a glass bulb so it is at the bottom when the lowest temp being measured is in the environment. A mixture of pure ice and water is used as a first calibration point and the human body temp, set at 96 degrees, was the second How do we know that there is a coldest possible temperature? Because an extrapolation to lower temperatures shows where pressure becomes zero and negative pressure is not possible; meaning absolute zero is the coldest temp. Why did Fahrenheit use 64 degrees between his calibration points? 64 degrees allows for repeating bisecting lines so there thermometer can be halved into fourths, eights, and so on to accurately read any temp. Why are there two flat portions to the warming curve for water? Why is the sample at constant temperature even though heat is being added? The 2 flat portions are for when water goes from a solid to liquid and later when it goes from liquid to gaseous. The energy is being used to free water molecules from the solid and liquid states, meaning that a high heat of fusion is needed to make this change take the energy in What assumptions explain the ideal gas law? Gasses are composed of tiny atoms/molecules that collectively occupy a tiny fraction of the volume the gas is confined to. The atoms don't interact with each other. The pressure on the walls of the container arises from collisions between the atoms/molecules and container walls What do the gas laws teach us about the physical meaning of temperature? By considering the change in momentum of the molecules colliding with the wall and the time between such collisions we discover a relationship between kinetic energy of translation and temp. this allowed for creating of Boltzman's constant How does the physical meaning of temperature account for the two types of planets? Inner allow hydrogen to escape (closer to the sun); outer don't (further) Why do hot air balloons float? Hot air balloons have heated air in them so they have less molecules present inside the balloon and less weight so there is an upward net force What were the first two metals smelted from ore? Copper and tin What happened when copper and tin are mixed together? It makes bronze, an alloy harder than the two metals themselves What were the desirable traits of bronze? Far harder than copper and has less slipping between the layers of atoms that make it up which made it the first abundant material for practical tools What was the presumption of alchemy? If mixing metals created new properties as seen in bronze, a recipe may exist that will change cheaper metals into one with all the properties of gold Why were alchemists sometimes called puffers? They sometimes used bellows to fan a charcoal fire to reach higher temperature flames Iron is found in abundance in the earth's crust. Why did it take so much longer for iron to be in use than bronze? It requires much higher temps to work that bronze which meant it couldn't be worked until high powered bellows had bee developed What did Lavoisier learn about mass in chemical reactions? He learned that mass was conserved in chemical reactions What led to the idea of "families" of elements? Families of elements were discovered as they each reacted similarly to different stimuli. For example, alkali metals are similar when isolated with electric currents while other react strongly with water or other are all easily formed salt compounds What was interesting about triads? The weight of the middle member was very nearly exactly half way between the mass of the lightest and heaviest members What did Mendeleev do? Why do we still use his table today? He assigned each element of weight to place them in a numbered table and accounted for elements that had not yet been discovered, leaving gaps for them as they were which made the table easy to adapt What did Mendeleev expect about atomic weights and our list of existing elements in his time? He assigned each element a weight but falsely believed that it was the weight that determined chemical properties and not the number of positive charges in the nucleus. He believed we had not discovered all of the elements and left room for newly discovered ones to be placed How was argon discovered? What led to its name? nitrogen was extracted from air and from the decomposition of ammonia which had different densities. This was traced back to a third gas in air besides nitrogen and oxygen called argon, or the "lazy one" because if couldn't be reacted with any known element How was helium discovered? 1868- its spectrum was detected in the solar atmosphere during a solar eclipse What do all points on a rotating wheel have in common? Points on a wheel move in circles; even though points further from the axel move with higher speeds, every point completes one revolution in the same amount of time How do we define the direction of a rotation? It lies along the axis of rotation (the axle) with the positive direction for a rotational movement being defined as clockwise or the advance of a right handed screw What determines the moment of inertia of an object? The object's mass and distribution of the mass relative to the axis of rotation What is the desirable property of a flywheel? The flywheel on early steam engines had a very large moment of inertia with as much mass located at the rim of the wheel Why do steam engines use a large flywheel? To get a large moment of inertia by distributing the wright far from the axis of rotation (axel) What is torque? The agent of change of angular momentum as it tends to create angular motion like a wrench tightening a bolt Why do we sometimes use wrenches that have a very long handle? The longer the handle, the greater the torque (angular momentum) that a given force will produce What is a central force? Acts along a line from the center of force to the object so the leer arm is always zero since the force goes through the axis, making torque zero; ex: gravity Why do central forces conserve angular momentum? Angular momentum is conserved as there is no torque as the force goes through the axis What force shapes the universe? Gravity (central force) Why is conservation of momentum important in explaining the shapes of astronomical objects? ????? What can a spinning ice skater do to increase their rotational speed? The skater can pull her arms in to change the moment of inertia increasing the velocity as angular momentum must be conserved Why do orbiting bodies have an angular momentum barrier that prevents their getting close to the central body? If the earth were to get closer to the sun its speed would have to increase to conserve angular momentum which gravity doesn't have the strength to provide the kinetic energy to get earth closer to the sun What examples of disk shapes exist in the universe? Why are disk shapes so common in the universe? The orbits of the 8 planets in the solar system nearly lie in a disk with all planets and moons revolving in the same direction except Uranus; Saturn's ring system is another example with dust and ice condensed into a disk. Finally spiral galaxies have distinct disk shapes made up of young and old stars How can a point of stable equilibrium be located on a potential energy curve? The minimum is a point of stable equilibrium so an object with a small amount of energy above the minimum will display motion that is at least approximately simple harmonic Why is simple harmonic motion common in nature? The motion near a minimum is always approximately simple harmonic What are turning points? Where a pendulum reverses direction of motion Consider a mass attached to a spring. What determines the period of the motion? The stiffness of the spring changes the period, with stiffer springs having larger k values and smaller periods and larger periods What happens to the period if the mass is increased? What happens if a stiffer spring is used? If mass is increased the period will be larger and if stiffer spring is used the k value will be higher leading to smaller period What happens to the period of simple harmonic motion when the amplitude is doubled? Nothing, it remains constant What happens to the total energy in a simple harmonic oscillator if the amplitude is doubled? It is increased four times the amplitude is squared What determines the phase in simple harmonic motion? Where the curve begin on the sine or cosine cycle determines the phase What did Planck deduce about simple harmonic oscillators in hot surfaces? He realized that observations made about light produced by hot surfaces had properties that could only be explained by restricting values of energy in simple harmonic motion to equally spaced levels Why is it relatively easy to make clocks and watches that keep good time? Clocks and watches can use pendulums and balance wheels to keep good time because the period of a simple harmonic doesn't depend on the amplitude of the motion, meaning the mechanism that keeps the mechanism doesn't have to function perfectly What is a wave? A wave is an oscillation that travels through matter or space accompanied by the transfer of energy How is wavelength define? How is period defined? The uniform distance between the crests of a wave. The time between crests of a wave How is period related to frequency? The reciprocal of the period and is measured in Hertz How is the speed of a wave related to its frequency and wavelength? Speed is the wavelength multiplied by the frequency What determines the speed of a wave on a stretched string? The string's tension What are the two kinds of wave motion? What phenomena are transverse waves? Transverse waves and longitudinal waves & The waving motion as seen in strings of musical instruments and on the surface of water (ex. Light) What phenomena are longitudinal? Air molecules moving back and forth along the direction of the propagation of the wave making sound (ex. Slinky, sword) Why are there two solutions to the wave equation for waves on a stretched string? What do the solutions represent? There are two solutions with the only difference being the minus sign so as t gets larger x must get more negative to follow the phase of the wave. This is because the wave can move in the positive or negative x direction What does the equation for waves on a stretched string predict about such waves? It predicts the speed of the propagation of the waves and the waves in both directions What kind of waves are sound waves? How is the energy of sound waves carried from place to place? Sound waves are longitudinal waves that are air molecules that move back and forth along the direction of the propagation of the wave What kind of waves are light waves? What waves in light? How is the energy in light carried from one place to another? ???? What is the fundamental property of waves? How can wave properties be distinguished from particle ones? Superposition is a fundamental wave property meaning that whenever 2 waves arrive at a given point the net wave disturbance is the sum of the two waves and can be either constructive or destructive, unlike I particle ones Why did Newton favor the "corpuscular" view of light? Newton preferred it as he imagined light to be the representation of flight paths of particles, though this theory was displaced by 1802 What is spectroscopy? Spectroscopy uses arrays of narrowly spaced slits to study wavelengths of light with extreme precision to reveal details about light emitted by hot surfaces and atoms What new theory was needed to explain spectroscopic observations? Quantum theory What does Newton's Principia describe? An understanding of nature through a fundamental understanding of motion and the mathematical form of gravitational force What evidence exists for two kinds of electric charge? The quantity of charge can exist as a Coulomb which is a stationary charge and electrostatic charges as moving charges; electrostatic effects result from stationary charges and magnetic effects result from moving charges What is Coulomb's law? What does it describe? Describes electromagnetism claiming the strength of the interaction is proportional to the magnitude of the charge on each of the 2 interacting bodies inversely proportional to the square of the distance between them How are gravity and the Coulomb force similar? How are they different? They have identical mathematical form but electrical force is much stronger than gravitational force; galaxy and solar system are bound by gravity while electrical force binds atoms; electric charge has two kinds while all matter attracts other matter; there is also no gravitational repulsion Why do most physics texts assume that electrical currents are moving positive charges when it's actually electrons that move? The assignment of the definitions of positive and negative derive from Franklin and if they were starting now it would likely be reversed What important role did Franklin play in the American Revolution? Franklin's diplomacy with France was his important role in the American Revolution What two kinds of discoveries were made possible by the development of chemical batteries? The discovery of magnetic effects including electromagnetic field theory and several new chemical elements to be discovered including sodium and potassium What two accidental discoveries were made by Galvani? An electrostatic generator device was causing contractions in a severed frog leg; a frog hung from an iron trellis with a bronze hook had violent contractions. He thought that animals generated some kind of natural electricity. The muscles were responding to current from two different voltage sources How is electrical power related to current and voltage? Power is the product of current and voltage How is the strength of an electric field defined? It is defined at a point in space as being the force per unit charge. How is electrical resistance defined? What determines the resistance of a wire? Resistance is an electrical quantity that measures how a device reduces electric flow though it. It is determined by length, diameter, and resistivity. Why did Tesla's AC power dominate over Edison's DC? Tesla had superior transmission technology as there was less loss in transition, meaning that from Niagara Falls, Edison could serve only a one mile radius while Tesla could serve much of New England What does Gauss's law describe? It is a mathematical formulation describing the origin of electric fields; the law is one of the cornerstones of electromagnetic theory How is the strength of an electric field related to the number of field lines? The electric field strength is proportional to the number of lines per area What two accidental discoveries were made by Galvani? What did he think he had discovered? What was actually happening? First he discovered an electrostatic generator, when touching a dissected frog leg through a scalpel, would make the leg contact. He then discovered that a frog hanging from a bronze hook would violently contract. He believed this meant that animals generated some kind of natural electricity, which was incorrect. The muscles were actually responding to current from two different volt sources What did Volta figure out? What device came out of his discovery? He stacked layers of silver and zinc separated by parchment soaked in salt solution. He realized that metals were reacting chemically and that they chemical reaction taking place in each cell produced a voltage. By staking many cells into a pile, a battery could be made that could produce a substantial flow of charge How is an electric circuit like the human circulatory system? The battery pumps out charge which circulates through the circuit then returns to the pump like how the heart pumps blood to be circulated What was discovered about compass needles near a current carrying wire? The compass would be deflected near a current carrying wire; the compass surrounding a wire all point along a tangent of a circle surrounding the wire What does Ampere's law describe? Ampere developed a mathematical formulation that allowed the calculation of the magnetic fields produced by various current configurations. Ampere's law imagines a surface with a conductor moving charge through the surface What is the shape of the magnetic field around a wire? Where do lines of magnetic field begin and end? How does this compare to lines of electric field? The lines of a magnetic field are circular around the current and being an end on themselves. The lines of an electrical field originate positive and radiate outwards negatively What is Faraday's law? What does it change about electricity and magnetism? Describes a fundamental coupling between electric and magnetic fields; this law shoes that energy in a magnetic field can be transformed into energy in an electric field What determines the energy density in space where electric and magnetic fields exist? The amount of energy present per unit volume is proportional to the square of the field intensity What important skill did Maxwell bring to the study of electromagnetism? Math What did Maxwell assume about nature and symmetry in electromagnetism? How is this related to the displacement current? Assumed a fundamental symmetry in nature and that if a chaining magnetic field produces an electric field, then a chaining electric field could produce a magnetic field. A changing electric field could create the same effect as an actual flow of charge which is called the displacement current What experimental evidence existed for the "displacement current" when Maxwell postulated its existence? None existed at that time What are two testable predictions are made by Maxwell's theory? Predicted that electromagnetic radiation could be both created and detected Describe four predictions of Maxwell's theory a. Predicts that the speed of light will not be affected by motion of the source or observer b. The waves will propagate with a speed related to constants c. Periodic acceleration of electric charge will produce electromagnetic radiation with the frequency of the periodic acceleration d. The electric and magnetic fields will oscillate in directions that are perpendicular to each other and the direction of propagation What did Henrich Hertz do? Succeeded in transmitting and detecting radio waves in the 1880s How are the discoveries of Galvani and Hertz fundamentally different? Galvani's discoveries were lucky while Hertz's were discovered through testing theories The return of Halley's comet was a famous test of Newton's theory. How were the observations of Hertz a second famous test of theory? Hertz produced and detected radiation with the predicted properties. The manufacture and detection of the electromagnetic radiation predicted by electromagnetic field theory was a major triumph of the scientific method. What does an electric generator do? It transforms energy in falling water or fossil fuels into electrical energy. What is the principle behind the electric generator? Magnetic forces drive charge through the circuit. The repelling effect of the static and induced fields allow mechanical energy to be converted into electrical energy. Why does driving with your headlights on reduce fuel efficiency? The alternator output needs to be strong to light the headlights, charge the battery, and run the car. What popular lab equipment made technical discoveries inevitable in the second half of the 1800's? large induction coils and batteries Why is Tesla's induction motor an important step forward? Tesla realized that a motor could be built without brushes which would prevent the current from created sparks and burning up What is the primary application of three phase power? It is used in most manufacturing motors because it doesn't need a lot of service Why were light and sound thought to be the same phenomena? Both show superposition What did electromagnetic field theory predict about the speed of light? It will be relate to the two constants associated with the origin of electric magnetic fields What did Einstein realize from his though his thought experiment about the wake of a boat? The wake maintains a constant position relative to the observer so the disturbance isn't a wave What did the Michelson-Morley Experiment show about the speed of light? Why did they consider this a failure? It was very different from the speed of sound. They weren't able to confirm it through observation. The speed of sound is not the same in all directions due to the effect of wind. These guys were following Maxwell's difference of the speed of light in different directions. No difference was found so earth is not moving through the expected medium for light. What aspect of the Michelson-Morley would raise health and safety concerns today? The apparatus they made was mounted on a piece of stone that was floating in a large vat of mercury What is an inertial observer? Observers that are not accelerating What is special about special relativity? ???? What is the first postulate of relativity? All observers measure exactly the same speed for light regardless of their relative motion Why does the first postulate create a "democracy" of observers? All observers see the same value How is this democracy related to the second postulate of relativity? Since all observers see the same values, the laws of physics must be the same for all the observers What are the predictions of special relativity? ???? Describe two ways in which the special theory of relativity has been tested. ???? What is time dilation? When intervals of time seem longer to the observer than they actually are. The time interval between two events is different for different observers. We would see time in a passing space ship as passing more slowly than around us What is the twin paradox? How is it resolved? A contradictory theory that says if one twin stays at home while another travels on a space trip near the speed of light then they should each be younger when they meet, which isn't possible; accelerating observers are not dealt with in special relativity so the traveling twin is in fact younger What is the relationship between mass and energy? Any object that has mass has energy waiting to be liberated; specifically e=mc2 How did nuclear fission prove special relativity? The fission fragments contained large amounts of energy and less mass than original substance; the mass lost multiplied by the square of the speed of light was equal to the energy liberated Why do we say that the speed of light is the "cosmic speed limit"? as the speed of light is approached, the denominator of the acceleration goes to infinity, so the acceleration goes to zero; the denominator is the mass of the object What is rest energy? Given by E=mc2. The fact that the constant of proportionality is the square of the speed of light is significant. Since the speed of light is a large value, its square is huge. A small amount of mass releases a huge amount of energy Why was the possibility of nuclear fission overlooked for so long? The failure of alchemy to change nuclei gave us the incorrect idea that nuclear structures could not be changed. The evidence of possible dramatic energy release was present but the process that would produce fission was beyond the imagination of nuclear physics at the time What is the uv catastrophe? How did theory and observation compare? The idea that infinity power could be radiated at short wavelengths. Theory produced a prediction that was a disaster. What was the origin of the uv catastrophe? Blackbody radiation; a failure to recognize that energy was quantized What two things did Planck do that got quantum theory started? The mathematical form of the blackbody spectrum and that a mechanical system restricted to discrete energy levels separated by equal steps gave rise to the observed blackbody spectrum. Describe two clues about the quantum nature of the universe. The allowed energies of a simple harmonic oscillator are separated by equal amounts. Quantum theory must predict a constant probability of decay per unit time for radioactive nuclei. What did JJ Thomson discover? What did this tell us about atoms? Electrons; atoms are made of a nucleus and electrons What three technical developments made new discoveries in physics about 1900? Film, vacuum pumps, and the spark coil How did Einstein interpret the photoelectric effect? What was new about this? The idea that it was actually bundles of energy; this idea gave light a dual nature What is the relationship between the frequency of electromagnetic radiation and the momentum carried by each of the photons? It is essentially the momentum of the photon alone; energy=momentum x speed of light What is the Compton effect? What does it prove about light? The scattering of photons by electrons; proves that light has a particle nature What new effect did the Curie's discover? Developed a method to separate previously undiscovered elements that were "radioactive" from uranium ore waste. They discovered radioactivity and half-life What is the radioactive decay law? What is meant by half-life? Radioactivity diminishes in an exponential fashion. The time required for a matter's activity to diminish to half of its value What does the radioactive decay law tells us about a complete quantum theory? The probability of decay per unit time is constant and a modern quantum theory must explain that What did Rutherford discover about atoms in the famous scattering experiments? They are actually mostly empty space with nearly all the mass concentrated in the nucleus Who actually took the data? Specifically what did the data show? Geiger and Marsden; the number of particles scattered per unit time as a function of an angle; the alpha scattering was particles bouncing off a point-like nucleus What two new ideas went into Bohr's model of the atom? Bundles of energy; photons and the nuclear atom with orbiting electrons What are the assumptions of the Bohr model? The atom gives off or absorbs energy as it makes a transition from one state to another; the energy of the photon absorbed or given off is equal to the difference in the energies of the two allowed states What does the Bohr model correctly predict? The energies absorbed and emitted by the hydrogen atom; the energy of the most energetic x-ray emitted by atoms as a function of their atomic number What does the model fail to predict? The visible wavelengths emitted by all other elements What is the de Broglie Hypothesis? What does it explain about the Bohr model? The idea that the relationship between wavelength and momentum observed for photons also applied to particles like electrons; it showed that the Bohr model is the superposition of the matter waves predicted by the hypothesis What three things were known by 1915 that must be predicted (explained) by a modern quantum theory? a. The energies given by the Bohr model for electrons moving under coulomb potential b. Equally spaced energy levels for the simple harmonic oscillator c. Involve the superposition of wave behavior