Phys 116, Winter 2003 

Chapter 27 & 28 review When 230nm light falls on a metal, the current through a photoelectric circuit is brought to zero at a reverse voltage of 1.64 V. What is the work function of the metal? Calculate the ionization energy of triply ionized beryllium, Be^{3+}, which has Z = 4. B) what wavelength photon would be required to ionize a trivalent beryllium cation, Be^{3+}, and give the ejected electron a kinetic energy of 10.0 eV? C) if the Bohr orbit of this cation was 0.500 mm, what is the value of n for a Bohr orbit of this size? D) What would the electrons energy be? The neutrons in a parallel beam, each having kinetic energy of ¼ eV, are directed through two slits 0.750 mm apart. How far apart will the interference peaks on a screen 2.50 m away be? How accurately can the position of a 3.00keV electron be measured assuming its energy is known to 1.00 %? m_{e }= 9.11 x 10^{31} kg. An electron in the 2p level in hydrogen remains there on the average of 10^{8} seconds before jumping to the 1s level. (a) Estimate the uncertainty in the energy of the 2s state. Part (b) What fraction of the total transition energy is this? Part (c ) What is the wavelength of this line in the spectrum of hydrogen? The central bright fringe of a diffraction pattern of electrons extends to either side of the midpoint, according to an angle q given by sin θ = λ/W, where λ is the de Broglie wavelength of the electron and W is the width of the slit it passes through. When λ = W, θ = 90°, and the central fringe fills the entire observation screen. In this case, an electron passing through the slit has roughly the same probability of either hitting the screen straight ahead or anywhere off to one side or another. Imagine Planck’s constant were large enough that you could exhibit similar effects when you walk through a 0.90m doorway. Your mass is 82 kg and you walk through at 0.50 m/s. How large would Planck’s constant have to be in this hypothetical world? Which of the following is not true of de Broglie’s hypothesis: (a) explains the diffraction pattern that a beam of electrons produces as it passes through two narrowly spaced apart slits. (b) explains the Compton effect. (c) states that the wavelength of matter is λ = h/p. (d) explains the scattering pattern that neutrons have when it strikes matter. (e) explains the average radius of an electron in a Bohr atom. The following experiments or effects do not support the hypothesis that light behaves as particles: (a) the diffraction of electrons when they pass through two narrowly spaced apart slits. (b) electronpositron pair production (c) the photoelectric effect (d) the Compton effect (e) black body radiation function. Given that Bohr’s hypothesis worked for all atoms, an emission spectrum of an unknown element revealed several lines leading to the energy levels of the electrons. Which of the following can be a possible sequence of four successive energy levels. (lowest energy level is either n=1, 2 or 3) (a) 170 eV, 37.8 eV, 9.44 eV, 5.33 eV, (b) 170 eV, 37.8 eV, 21.25 eV, 9.44 eV, (c) 37.8 eV, 21.25 eV, 9.44 eV, 5.33 eV; (d) 37.8 eV, 21.25 eV, 13.6 eV, 9.44 eV, (e) –340 eV, 170 eV, 21.25 eV, 13.6 eV. Which of the following elements is the atom likely to be? a) Li b) Be c) B d) N e) Ne The Greek symbol ψ is called a wave function of an electron, as described by Schrödinger, represents (a) the electric field strength of the electron, (b) the density of electrons at some point in space around a nucleus, (c) a prediction of the path an electron around a nucleus (d) the amplitude of the electron matter field, (e) the frequency of the electron matter field. From electronic spectra, Bohr determined that, in the ground state, the electron was found at a radius of 5.29 x 10^{11} m and a speed of 2.18 x 10^{6} m/s. Which of the following does such an idea violate: (a) Pauli exclusion principle (b) de Broglie’s hypothesis, (c) Wien’s law (d) principle of complementarity, (e) the indeterminancy principle.


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