Transcript Document
Review The Wave Nature of Light Important: When a light wave travels from one medium to another, its frequency does not change, but its wavelength does. 1. Why we do not notice any dispersion when light passes through a windowpane? 1. What does the dispersion of light tell us about the speeds of various colors of light in a material? 2. Will the converging lens focus blue light or red light at a closer distance to the lens? Explain. Interference: Young’s Double Slit Experiment Constructive Interference: Destructive Interference: d sin m ; m 0,1,2..... 1 d sin (m ) ; 2 m 0,1,2..... 1. Would yellow light or green light produce the wider twoslit interference pattern? 2. If light and sound are both wave phenomena, why can we hear sounds around a corner but cannot see around a corner? 3. Red light is used to form a two-slit interference pattern on a screen. As the two slits are moved farther apart, does the separation of the bright bands on the screen decrease, increase, or remain the same? Diffraction by a Disk Diffraction by a Single Slit Limits of Resolution The ability of lens to produce distinct images of two point objects very close together is called the resolution of lens. 1. Why can’t an ordinary microscope using visible light be used to observe individual molecules? 2. Is it better to use red light or blue light to minimize diffraction effects while photographing tiny objects through a microscope? Why? 3. Why are the diffraction effects of your eyes more important during the day than at night? Interference by Thin Film A beam of light reflected by a material whose index of refraction is greater than that of the material in which it is traveling, changes phase by ½ cycle. Polarization 1. Can sound waves be polarized? Early Quantum Theory and Models of the Atom Discovery of Electron Rutherford’s Model Blackbody Radiation A blackbody is a body that would absorb all the radiation falling on it. Planck’s Quantum Hypothesis Planck’s assumption suggests that the energy of any molecular vibration could be only some whole number multiple of hf: Emin nhf ; n 1,2,3.... 1. If all objects emit radiation, why don’t we see most of them in the dark? 2. Rutherford’s model provided an explanation for the emission of light from atoms. What was this mechanism and why was it unsatisfactory? 3. Suppose you were a nineteenth-century scientist who had just discovered a new phenomenon known as Zeta rays. What experiment could you perform to define if Zeta rays are charged particles or e/m waves? Could this experiment distinguish between neutral particles and an e/m wave? The Photoelectric Effect 1. An increase in intensity of the light beam means more photons are incident, so more electrons will be ejected , but max KE in not changed. 2. If the frequency of the light is increased, the max KE increases linearly. 3. If the frequency f is less than the “cutoff’ frequency f0, no electrons will be ejected at all, no matter how big is the intensity. 1. If a metal surface is illuminated by light at a single frequency, why don’t all the photoelectrons have the same kinetic energy when they leave the metal’s surface? 2. What property of the emitted electrons depends on the intensity of incident light? 3. What property of the emitted photoelectrons depends on the frequency of incident light? Bohr’s Model Allowed Angular Momenta h Ln n 2 Bohr’s Second Postulate An electron doesn’t radiate when it is in one of the allowed orbits. Bohr’s Third Postulate A single photon is emitted whenever an electron jumps down from one orbit to another. 1. Why do astronomers often use the terms color and temperature interchangeably when referring to stars? 2. Why did Bohr assume that the electrons do not radiate when they are in the allowed orbits? Wave Nature of Matter De Broglie Wavelength h mv The Heisenberg Uncertainty Principle h xp 2 34 1.06 10 J s 1. Why do astronomers often use the terms color and temperature interchangeably when referring to stars? 2. Why did Bohr assume that the electrons do not radiate when they are in the allowed orbits? Wave Nature of Matter De Broglie Wavelength h mv The Heisenberg Uncertainty Principle h xp 2 34 1.06 10 J s Particle in a Box Quantum Mechanics of the Hydrogen Atom n – principal quantum number, positive integer; l – orbital quantum number, is related to the magnitude of the angular momentum of the electron; at given n can take integer values from 0 to (n-1); ml – magnetic quantum number, is related to the direction of the electron’s angular momentum, and it can take an integer values from –l to +l. Selection Rule Another prediction of quantum mechanics is that when a photon is emitted or absorbed, transitions can occur only between states with values of l that differ by one unit. The Exclusion Principle No two electrons in an atom can occupy the same quantum state. 1. How many electrons have the quantum numbers n=5 and l=1? 2. How many electrons can have the quantum numbers n=5 and l=4? 3. Why do some minerals glow when they are illuminated with ultraviolet light? Radioactivity Alpha Decay Transmutation parent daughter Beta Decay Gamma Decay 1. Which of the three types of radiation will interact with electric field? 2. Why do beta rays and alpha rays deflect in opposite directions when moving through a magnetic field? 1. What happens to the charge of the nucleus when it decays via beta plus decay? 2. What happens to the charge of the nucleus when it decays via electron capture? 3. What changes in the numbers of neutrons and protons occur when a nucleus is bombarded with a deuteron (containing one neutron and one proton) and an alpha particle is emitted? Half-Life and Rate of Decay 1. You place a chunk of radioactive material on a scale and find that it has a mass of 4 kilogram. The half-life of the material is 10 days. What will the scale read after 10 days? 2. A radioactive material has a half-life of 50 days. How long would you have to watch a particular nucleus before would see it decay?