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Chapter 6: Q3DQ (page 1274)
According to the photon model, light carries its energy in packets called quanta or photons. Why then don鈥檛 we see a series of flashes when we look at things?
We can鈥檛 see a series of flashes when we look at things due to high speed of photons and the large amount of photons.
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A sample of hydrogen atoms is irradiated with light with wavelength 85.5 nm, and electrons are observed leaving the gas. (a) If each hydrogen atom were initially in its ground level, what would be the maximum kinetic energy in electron volts of these photoelectrons? (b) A few electrons are detected with energies as much as 10.2 eV greater than the maximum kinetic energy calculated in part (a). How can this be?
The energy-level scheme for the hypothetical one electron element Samarium is shown in Fig below. The potential energy is taken to be zero for an electron at an infinite distance from the nucleus. (a) How much energy (in electron volts) does it take to ionize an electron from the ground level? (b) An 18-eV photon is absorbed by a Samarium atom in its ground level. As the atom returns to its ground level, what possible energies can the emitted photons have? Assume that there can be transitions between all pairs of levels. (c) What will happen if a photon with an energy of 8 eV strikes a Samarium atom in its ground level? Why? (d) Photons emitted in the Samarium transitions n = 3 鈫� n = 2 and n = 3 鈫� n = 1 will eject photoelectrons from an unknown metal, but the photon emitted from the transition n = 4 鈫� n = 3 will not. What are the limits (maximum and minimum possible values) of the work function of the metal?
The theory of relativity sets an upper limit on the speed that a particle can have. Are there also limits on the energy and momentum of a particle? Explain.
Iodine in the body is preferentially taken up by the thyroid gland. Therefore, radioactive iodine in small doses is used to image the thyroid and in large doses is used to kill thyroid cells to treat some types of cancer or thyroid disease. The iodine isotopes used have relatively short half-lives, so they must be produced in a nuclear reactor or accelerator. One isotope frequently used for imaging is ; it has a half-life of 13.2 h and emits a 0.16-MeV gamma-ray photon. One method of producing is in the nuclear reaction . The atomic masses relevant to this reaction are , 122.904270 u; , 122.905589 u; n, 1.008665 u; and , 1.007825 u. The iodine isotope commonly used for treatment of disease is , which is produced by irradiating in a nuclear reactor to form . The then decays to . undergoes beta- decay with a half-life of 8.04 d, emitting electrons with energies up to 0.61 MeV and gamma-ray photons of energy 0.36 MeV. A typical thyroid cancer treatment might involve administration of 3.7 GBq of .
Which reaction produces in the nuclear reactor?
(a) ;
(b) ;
(c) ;
(d) .
A maser is a laser-type device that produces electromagnetic waves with frequencies in the microwave and radio-wave bands of the electromagnetic spectrum. You can use the radio waves generated by a hydrogen maser as a standard of frequency. The frequency of these waves is 1,420,405,751.786 hertz. (A hertz is another name for one cycle per second.) A clock controlled by a hydrogen maser is off by only in 100,000 years. For the following questions, use only three significant figures. (The large number of significant figures given for the frequency simply illustrates the remarkable accuracy to which it has been measured.)
(a) What is the time for one cycle of the radio wave?
(b) How many cycles occur in 1 hr?
(c) How many cycles would have occurred during the age of the earth, which is estimated to be ?
(d) By how many seconds would a hydrogen maser clock be off after a time interval equal to the age of the earth?
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