Chapter 4: Problem 11
Calculate the wavelengths of the first three lines in the Balmer series for hydrogen.
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Chapter 4: Problem 11
Calculate the wavelengths of the first three lines in the Balmer series for hydrogen.
These are the key concepts you need to understand to accurately answer the question.
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A hydrogen atom initially in its ground state \((n=1)\) absorbs a photon and ends up in the state for which \(n=3 .\) (a) What is the energy of the absorbed photon? (b) If the atom returns to the ground state, what photon energies could the atom emit?
What is the energy of the photon that could cause (a) an electronic transition from the \(n=4\) state to the \(n=5\) state of hydrogen and (b) an electronic transition from the \(n=5\) state to the \(n=6\) state?
A Thomson-type experiment with relativistic electrons. One of the earliest experiments to show that \(p=\gamma m v\) (rather than \(p=m v\) ) was that of Neumann. [G. Neumann, \(A n n\). Physik 45:529 (1914)]. The apparatus shown in Figure P4.5 is identical to Thomson's except that the source of high-speed electrons is a radioactive radium source and the magnetic field \(\mathbf{B}\) is arranged to act on the electron over its entire trajectory from source to detector. The combined electric and magnetic fields act as a velocity selector, only passing electrons with speed \(v\), where \(v=V / B d\) (Equation 4.6), while in the region where there is only a magnetic field the electron moves in a circle of radius \(r\), with \(r\) given by \(p=B r e\). This latter region \((\mathbf{E}=0, \mathbf{B}=\) constant \()\) acts as a momentum selector because electrons with larger momenta have paths with larger radii. (a) Show that the radius of the circle described by the electron is given by \(r=\left(l^{2}+y^{2}\right) / 2 y\). (b) Typical values for the Neumann experiment were \(d=2.51 \times 10^{-4} \mathrm{~m}, B=0.0177 \mathrm{~T}\), and \(l=0.0247 \mathrm{~m}\). For \(V=1060 \mathrm{~V}, y\), the most critical value, was measured to be \(0.0024 \pm 0.0005 \mathrm{~m}\). Show that these values disagree with the \(y\) value calculated from \(p=m v\) but agree with the \(y\) value calculated from \(p=\gamma m v\) within experimental error. (Hint: Find \(v\) from Equation \(4.6\), use \(m v=B r e\) or \(\gamma m v=\) Bre to find \(r\), and use \(r\) to find \(y\).)
Steven Chu, Claude Cohen-Tannoudji, and William Phillips received the 1997 Nobel prize in physics for "the development of methods to cool and trap atoms with laser light." One part of their work was with a beam of atoms (mass \(\sim 10^{-25} \mathrm{~kg}\) ) that move at a speed on the order of \(1 \mathrm{~km} / \mathrm{s}\), similar to the speed of molecules in air at room temperature. An intense laser light beam tuned to a visible atomic transition (assume \(500 \mathrm{~nm}\) ) is directed straight into the atomic beam. That is, the atomic beam and light beam are traveling in opposite directions. An atom in the ground state immediately absorbs a photon. Total system momentum is conserved in the absorption process. After a lifetime on the order of \(10^{-8} \mathrm{~s}\), the excited atom radiates by spontaneous emission. It has an equal probability of emitting a photon in any direction. Thus, the average "recoil" of the atom is zero over many absorption and emission cycles. (a) Estimate the average deceleration of the atomic beam. (b) What is the order of magnitude of the distance over which the atoms in the beam will be brought to a halt?
Using the Faraday \((96,500 \mathrm{C})\) and Avogadro's number, determine the electronic charge. Explain your reasoning.
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