Final Test Review Tuesday May 4 th 10:00am to 11:50am Relativity Quantum Mechanics

Chapter 8 (revisited) Planetary Model of the Atom –Electron spins around the nucleus in a manner that is similar to how the planets rotate around the sun –Electron was discovered in 1897 –Nucleus was discovered in 1911 –Proton was discovered in 1914 –Neutron was discovered in 1932

Chapter 8 (revisited) Planetary model cont’d –Typical size of the nucleus is cm –Typical size of the outer electron orbit is cm Periodic Table –Mass number (A) tells you the number of protons and neutrons in the nucleus –Is found underneath the elemental symbol –round up the number you find on the periodic table.

Chapter 8 (revisited) Periodic Table cont’d –Atomic number (Z) tells you the number of protons and the number of electrons in the atom –To find the number of neutrons (N) in the nucleus, use the equation N = A - Z –A typical way to show the information in the periodic table is by using the convention X is the element symbol A Z X

Chapter 8 (revisited) Periodic table cont’d –Example – CA –Calcium has 20 electrons and 20 protons –Calcium has = 20 neutrons

Relativity Relative Motion –Motion where people/objects move with different speeds and directions with respect to one another Theory of relativity –Any theory that works out answers to questions concerning observers who are in relative motion.

Relativity The principle of Relativity –Every non-accelerated observer observes the same laws of nature. In other words no experiment performed within a sealed room moving at an unchanging speed can tell you whether you are standing still or moving.

Relativity The principle of the constancy of lightspeed –The speed of light, and all other electromagnetic radiation, in empty space is the same for all non-accelerated observers, regardless of the motion of the light source. –The speed of light is 3 x 10 8 m/s

Relativity Reference Frames –The laboratory or other surroundings within which the observer makes measurements. Measurements made in a particular reference frame are said to be relative to that frame.

Relativity Einstein’s theory of Relativity comes in two types. Each one deals with the motion of reference frames with one another. –Special relativity Reference frames move with constant velocity –General relativity Reference frames are accelerated

Relativity Five of Special Relativity’s most important predictions –1. The limiting speed in the universe is the speed of light. –2. Relativity of Time (time dilation) Fast moving clocks seem to slow down

Relativity Five of Special Relativity’s predictions cont’d –3. Relativity of space (length contraction) Fast moving objects appear to contract –4. Relativity of mass Fast moving objects appear to have an increase in mass

Relativity Five of Special Relativity’s predictions cont’d –5. E = mc 2 The principal of Mass-energy equivalence –Energy has mass, thus energy has inertia. Mass has energy, thus mass has the ability to do work. The energy and mass of a system is given by E = mc 2

Quantum Mechanics In 1900, Max Planck studied the emission of electromagnetic radiation from vibrating charged objects. His study led him to the hypothesis that an oscillating atom can absorb or re-emit energy in discrete bundles called “quanta”.

Quantum Mechanics cont’d In 1905, Albert Einstein used Planck’s idea of quantized energy to explain the photoelectric effect. In the photoelectric effect (1887), scientists shined a beam of light on one of two metal plates in a vacuum sealed tube. Electrons were observed to travel from one plate to the other.

Quantum Mechanics cont’d Electromagnetism predicted that it should take about a month for an electron to be ejected from the surface of the metal plates. Einstein explained the photoelectric effect by stating two things: –All electromagnetic energy is concentrated in localized packets called photons. –The photon’s energy is given by the equation E=hf E = energy of photon h = Planck’s constant (6.6 x J / s) f = frequency of the electromagnetic wave.

Quantum Mechanics cont’d Particle Theory of Radiation –Electromagnetic radiation is created by vibrating, charged particles whose energy is quantized, that is, restricted to certain allowed values. –A particle of radiation, called a photon, is created when a charged particle jumps from one allowed state to another. –Energy of a photon is given by E = hf

Quantum Mechanics cont’d In taking a second look at Young’s Double slit experiment, one notices tiny point like impacts of the photons on the photographic screen. This leads one to ask: What is it that directs an individual photon to strike the screen at a point that will contribute to the appropriate interference pattern while still allowing each photon to strike randomly all over the screen? (actually there is no clear answer)

Quantum Mechanics cont’d Wave-particle duality of radiation –Radiation has wave-like and particle- like properties. Matter waves –De Broglie in 1923 suggested that matter could behave like a wave. – = h / ms wavelength of particle h Planck’s constant m mass of particle s speed of particle

Quantum Mechanics cont’d Wave theory of matter –Every material particle has wave properties with a wavelength,, given by the equation on the previous slide. Wave particle duality for matter –Matter has wave-like and particle- like properties.

Quantum Mechanics cont’d There is problem though in thinking of light and matter as having particle-like and wave- like properties. One must realize that an experiment can only detect / reveal the particle-like or wave- like properties of radiation and matter not both.

Quantum Mechanics cont’d In Quantum Mechanics, one is able to get statistical information about the probabilities of various things one can observed. This statistical information introduces a kind of indeterminacy into the framework of Quantum Theory and science in general.

Quantum Mechanics cont’d All Quantum Mechanics has to offer is statistical information about the possible results for one’s experiment. This indeterminacy has been disturbing to physicists and philosophers. Is it a peculiarity of nature? A deficiency in the theory? A fault in measurement? What?

Quantum Mechanics cont’d Quantum Mechanical model of the atom –Electron is confined to move around the nucleus in s,p,d, or f orbitals. –The atom has discrete energy states. The lowest of which is called the ground state. –This model has been useful in predicting the structure of solids and liquids and the emission and absorption of EM radiation in solids, liquids, and gases.

Quantum Mechanics cont’d Planetary Model of the atom –Doesn’t explain why electron doesn’t spiral into the nucleus. –Doesn’t explain why excited gas atoms would emit discrete spectral lines. –Quantum Mechanics provides the answer