Option E: The History and Development of Physics -------------------------------------------------------------------------- -------------------------------------------------------------------------- E.1 Astronomy and Development of Models of the Universe -------------------------------------------------------------------------- Astronomical observations E.1.1 Describe the observed motion of the stars during one night. Nightly arcs or circles of stars, centered around the "celestial pole" E.1.2 Describe the observed motion of the sun in the sky each day, and how this varies over the year, at different latitudes. Each day: sun rises from east and sets to the west Variation over the year / near the poles: the sun rises but not as high Variation over the year / near the equator: not so much variation E.1.3 Describe how the observed motions of the planets vary with time with respect to the stars. Blah E.1.4 Describe the observed motion of the moon during a lunar month. Blah -------------------------------------------------------------------------- Development of models of the universe Note: The structure and rationale of each model should be discussed, as well as its successes and limitations. Ideological perspectives and assumptions behind the models should also be included. E.1.5 Describe the Aristotelian/Ptolemaic model of the universe and explain how it accounted for the motions of the stars, sun, moon and planets. Aristotelian: The universe was finite, spherical and above it was heaven or whatever. Everything was divided into 4 elements...earth, water, air and fire (the fire being the sun). Everything below the orbit of the moon was the earth, everything above the ether. The ether moved independently of the earth, which is a nice way to explain everything without thinking about it. Aristotle believed everything moved in circular paths, and that the earth was at the center of the universe. Ptolemaic: "Heavenly bodies", such as the sun, moon planets and stars, orbited around the earth in circles, but there were little circles within these, to account for the fact that they didn't appear to match circles (called epicycles). There were eight levels, with the outermost being like a fixed roof of stars. E.1.6 Describe the Aristarchian/Copernican model of the universe and explain how it accounted for the motions of the stars, sun, moon and planets. Earth orbited the sun, and so did the other planets, but the moon orbited the earth. The stars were still like a fixed roof, out beyond the planets. Everything orbited in circles. E.1.7 Discuss the advantages of, and objections to, the heliocentric model. Objections: based primarily on religious issues, and enforced due to the close ties between the church and government. Gallileo defended the model, with observations of moons orbiting jupiter, however the church eventually forced him to publicly withdraw his support for the model. Advantages: fitted in nicely with the observations E.1.8 Discuss Kepler's model and his development of the three laws of planetary motion. Brahe (accurate data!): This model has the planets orbiting the sun, but the sun orbiting the earth, and was intended to be like a compromise between the church and Copernicus' model. Kepler: an extension of Copernicus', but has simple mathematical laws to describe the motions of the planets... 1) The planets orbited on elliptical paths, with the sun at the focus. 2) The planets orbited a segment of equal area in equal amounts of time, which meant when they were closer, they moved faster. 3) T2 is proportional to R3. (T is period, R is radius)...this means T12/T22 = R13/R23. -------------------------------------------------------------------------- Newton's synthesis E.1.9 Explain why Newton's law of gravitation is called a universal law. Newton's insight was in connecting the local earthbound phenomenon of falling objects with the force required to keep bodies like the moon in orbit about the earth. E.1.10 Describe and discuss the contributions of Newton to the derivation and explanation of Kepler's laws. Newton's law of universal gravitation gave a mathematical, and theoretical basis for kepler's model. F = Gm1m2/r2, and F = mv2/r and since v=rw, F = mrw² Gm1m2/r2 = mrw2, and w = ((2 x Pi) / T), so Gm1m2/r3 = m((2 x Pi) / T)2, so T2 is proportional to R3. Gravity provides the centripetal force necessary for Kepler's third law. -------------------------------------------------------------------------- -------------------------------------------------------------------------- E.2 Mechanics -------------------------------------------------------------------------- Development of concepts of motion, force and mass E.2.1 Describe and discuss the Aristotelian views of motion and force. To move an object, a force was required. To keep an object moving also required a force. Thus, the natural state of objects is at rest...there was no concept of friction. Natural state: objects strived to be more perfect when they moved towards their natural place E.2.2 Describe, discuss and apply the experimental methods used by Galileo to study motion. Galileo examined the motion of objects on rams...If it rolled down one, then up another, then it always ended at the original height, irrespective of the slopes (because friction was minimal). This lead to the conclusion that if an object rolled down a slope and along a flat surface, it should go on to infinity, as it would never reach it's original height. This was also important for the fact that he was using experiment, rather than theoretical reasoning based on untestable assumptions. E.2.3 Compare Newtonian and Aristotelian theories of motion, force and mass. Aristotelian: Matter-dominated (earth, water, air, fire), ether - Motions <- basic natures of the substances - Basic kinds of motion: - alteration/change (rusting) - natural local motion (up or down) Newtonian: Rigorously logical, axiomatic style - A number of definitions and assumptions - laws of motion and gravity - based on induction from experiment - Definitions: 1. Quantity of matter (nowadays mass) 2. Quantity of motion (= mv, nowadays momentum) 3. Inertia (inherent property of mass; its property to resist change of its state of uniform motion) E.2.4 Discuss the concept of mechanical determinism in the universe. According to mechanical determinism, if all forces acting on an object are known precisely at one instant, the future - and past - states of the object can be calculated. -------------------------------------------------------------------------- -------------------------------------------------------------------------- E.3 Concepts of Heat E.3.1 Describe and evaluate the phlogiston/caloric theory of heat. A theory of heat from the mid 1800s. Phlogistin was a substance contained within things, which, when burnt, was removed as heat, thus turning them into ashes. Caloric was the original name for heat, which was thought to be like a fluid, flowing from hot objects to cold ones. It could not, however, explain the production of heat through friction. E.3.2 Describe and discuss the contributions of Rumford and Joule to the demise of the caloric theory. Rumford: He measured the amount of heat developed from friction during the boring of a cannon; large amount of heat and small amount of shavings -> heat could not come from latent heat -> specific heat of shavings were the same as the original metal -> Rumford heat could be generated without shavings Joule: Showed that work can produce heat; Joule produced a successful experiment which used a falling mass to turn paddles and produced a measurable change in temperature. The change in energy of the falling mass could be found, and this energy was in part being given to the water by the turning paddles. Based on this, Joule unified the two forms of energy. E.3.3 Describe Joule's experiment to measure the mechanical equivalent of heat, interpret the results and solve related problems. A falling mass turns paddles and produces a measurable change in temperature. The change in energy of the falling mass can be found, and this energy was in part being given to the water by the turning paddles. P = W/t = Q/t -> Q = Pt Pt = C*m*^T ^PE = mgh = ^It = cm^T -------------------------------------------------------------------------- -------------------------------------------------------------------------- E.4 Electricity and Magnetism -------------------------------------------------------------------------- Discovery of natural electrification and magnetism E.4.1 Describe the early discoveries and investigations of electrification and electric effects. Amber/electrification by friction: Greek philosopher Thales -> “amber becomes magnetic!” English William Gilbert -> “Electrica” Amber/electrification by induction: Attraction and repulsion: Insulators: Du Fay: The experimental cords should be wrapped with some nonconductor so it would be insulated (so that current wouldn’t be lost) E.4.2 Describe the early discoveries and applications of natural magnetism. Lodestone: XXX Magnets: Rocks found in Asia Minor The compass: Haung Ti, around 376 B.C. Navigation: XXX Earth's magnetic field: XXX -------------------------------------------------------------------------- The concepts of electric charge, electric force and electric field E.4.3 Discuss the development of explanatory models for electrification and electric effects, leading to the modern concept of charge. Two fluid model of Du Fay: Two kinds of electricity -> two fluids: vitreous and resinous. When Du Fay electrified a glass rod, it attracted nearby bits of cork. When the cork bits were touched with the rod they however repelled one athor. Matter = neutral because it contains equal quantities of both fluids; this substance could be separated by friction from objects. Objections: XXX Single fluid model of Franklin: Only one fluid that can’t be created or destroyed; transferred by rubbing from one object to an other. Fluid = positive, lack of fluid = negative. Objections: XXX Modern atomic model of matter and concept of charge: Electrification is due to transfer or positive or negative charges. -------------------------------------------------------------------------- E.4.4 Compare the methods of Franklin/Priestley and Coulomb in establishing the inverse square nature of the electrostatic force. Franklin/Priestley: - Analogy between gravity and electricity - Inside a hollow sphere no electrical attraction; charge distributed uniformly on the surface - indirect method: when the d between two small charged bodies is increased by some factor, the forces between the bodies is reduced by the square of the factor Coulomb: Direct method - by experiments! E.4.5 Outline Coulomb's experiments that established the inverse square distance relation and the proportionality of force to charge magnitude. Experimental setup: + rod hanging from the ceiling -> a + charge brought near -> rod twisted -> from the angle the force could be calculated -------------------------------------------------------------------------- Magnetic effects of electric currents and electric effects of magnetic fields E.4.6 Describe and discuss the discoveries and investigations of Oersted and Ampere. Oersted: He brought a compass close to an electric wire -> needle jumped and pointed to the wire -> electric current creates a magnetic field! + Electric wire is deflected in a magnetic field. Ampere: “Magnetism is electricity in motion”; intuitive leap which he confirmed by experiment. A long wire carrying current I -> A current-carrying test wire near -> the force eexerted on the test wire is directly proportional to its length. If the current flows parallel -> wires attract; if the other current is reversed, the wires repel. E.4.7 Discuss Faraday's search for, and eventual discovery of, electromagnetic induction. Using a ring of soft iron wrapped in two windings of insulated wire -> one wire to a galvanometer, one to a battery -> when circuit was broken and connected again, meter recorded a pulse -> magnetism produced a current. -------------------------------------------------------------------------- -------------------------------------------------------------------------- E.5 Atomic and Nuclear Physics -------------------------------------------------------------------------- The electron E.5.1 Outline and discuss the discovery and investigation of cathode rays, hypotheses of their nature, and the discovery of the electron. Crookes: “Cathode rays = radiant matter, negatively charged particles” Europaeans: “Etherial disturbance, like light” Hertz: Noticed the rays passed through a thin sheet of gold. found (wrongly!) that the particles were not deflected in electric fields. (He had too much gas in the discharge tube.) Thomson studied conduction of electricity through gases. Thomson realized he could deflect the cathode rays in an electric field. -> He found out that the particles were 2000 times as light as hydrogen. Explanation of the Hertz’s gold thingy: particles of this size could pass between atoms in a solid. Thomson repeated his experiment with cathodes of different metals -> the mystery particles existed in many types of atoms, whee. E.5.2 Outline Thomson's experiment to measure the charge-to-mass ratio of the electron. High voltage -> cathode -> electrons between V plates + B field -> glow at the end of the tube; F = evB -> evB = mv²/r -> e/m = V/Br -> e/m = E/B²r -------------------------------------------------------------------------- The atom and the nucleus E.5.3 Compare Thomson's plum pudding model of the atom with Rutherford's nuclear model of the atom. Thomson: positively charged sphere with negatively charged electrons bouncing inside Rutherford: positively charged nucleus with negatively charged electrons whirling around it in circles E.5.4 Describe and discuss Chadwick's discovery of the neutron. Rutherford / Joliot-Curie’s experiment -> Chadwick: He bombarded the hydrogen atoms in paraffin with the beryllium emissions, and also used helium, nitrogen, and other elements as targets. By comparing the energies of recoiling charged particles from different targets, he proved that the beryllium emissions contained a neutral component with a mass approximately equal to that of the proton. -------------------------------------------------------------------------- -------------------------------------------------------------------------- E.6 The Quantum Concept and Atomic Models (HL only) -------------------------------------------------------------------------- Atomic spectra and the Bohr model of the atom E.6.1 Describe the atomic spectrum of hydrogen, the search for explanations and the discovery of the (empirical) Rydberg formula for spectral series. Rarefied gases can be excited to emit light (via heating). Excited gases emit only certain wavelengths. The spacing between lines in the H spectra decreases in a regular way -> Rydberg formula Lyman series (UV) -> Balmer series (UV + visible) -> Paschen series (IR) E.6.2 State the Bohr postulates as applied to the hydrogen atom. 1) Electrons going around in circular orbits 2) Only certain stationary orbits with certain energies (no em radiation!) 3) Electron de-excites -> a photon emitted 4) Angular momentum is quantized E.6.3 Derive the energy levels of the hydrogen atom. See the AnSa-paper E.6.4 Derive the Rydberg formula from energy level differences. YUCK! See the AnSa-paper E.6.5 Discuss the successes and limitations of the Bohr model. Successes: 1) Explained why atoms emit light spectra 2) Explained the spectrum for hydrogen 3) Explained absorption spectra 4) Ensured stability of atoms 5) Accurately predicted the ionization energy of 13.6 eV for hydrogen Limitations: 1) Only for hydrogen spectrum (and other 1-electronic ions) 2) Doesn’t explain stationary states 3) Doesn’t explain the fine structure of the spectrum 4) Doesn’t explain the intensity of the spectrum lines E.6.6 Solve problems on the Bohr model and spectra. -------------------------------------------------------------------------- The de Broglie hypothesis and the Schrödinger model of the atom E.6.7 Outline de Broglie's development of the concept of matter waves. Whee, there’s a deep symmetry in nature! -> If light is a particle and also a wave, then maybe also other particles have also a wave nature. E.6.8 Outline how the Schrödinger model of the atom leads to quantized energy states and quantization of emitted radiation. The model assumes that electrons in the atom can be described by wave functions. These have to fit boundary conditions in three dimensions in the atom, giving rise to both radial and angular allowed modes with discrete energy states (analogous to the discrete allowed frequencies of standing waves). The electron has an undefined position, but the square of the amplitude of the wave function gives the probability of finding it at a point. E.6.9 Compare and contrast the Bohr and Schrödinger models of the atom. Students should be able to comment on the assumptions, applicability, limitations, successes, etc of these models. -------------------------------------------------------------------------- The Heisenberg uncertainty principle and the loss of determinism E.6.10 Outline the Heisenberg uncertainty principle with regard to position&momentum and time&energy, and discuss its implications on determinism. There is a limit to the accuracy of measurements -> uncertainty is inherent in nature. At one instant we can know accurately either position or momentum of the electron - or energy / time. Effect on determinism: Whoops, we can't predict the future. Formulae: (^ = delta) - ^x =~ wavelength - ^p =~ h/wavelength - -> uncertainty = ^x*^p >= h/2pi - ^t =~ wavelength/c - ^E =~ hc/wavelength - -> uncertainty = ^t*^E >~ h/4pi