Conceptual Questions

ssm Solution is in the Student Solutions Manual

| 1 | The photons emitted by a source of light do not all have the same energy. Is the source monochromatic? Give your reasoning.

| 2 | Which colored light bulb—red, orange, yellow, green, or blue—emits photons with (a) the least energy and (b) the greatest energy? Account for your answers.

| 3 | Does a photon emitted by a higher-wattage red light bulb have more energy than a photon emitted by a lower-wattage red bulb? Justify your answer.

| 4 | When a sufficient number of visible light photons strike a piece of photographic film, the film becomes exposed. An X-ray photon is more energetic than a visible light photon. Yet, most photographic films are not exposed by the X-ray machines used at airport security checkpoints. Explain what these observations imply about the number of photons emitted by the X-ray machines.

| 5 | Radiation of a given wavelength causes electrons to be emitted from the surface of one metal but not from the surface of another metal. Explain why this could be.

| 6 | ssm In the photoelectric effect, suppose that the intensity of the light is increased, while the frequency is kept constant. The frequency is greater than the minimum frequency f0. State whether each of the following will increase, decrease, or remain constant, and explain your choice: (a) the current in the phototube, (b) the number of electrons emitted per second from the metal surface, (c) the maximum kinetic energy that an electron could have, (d) the maximum momentum that an electron could have, and (e) the minimum de Broglie wavelength that an electron could have.

| 7 | In a Compton scattering experiment, an electron is accelerated straight ahead in the same direction as that of the incident X-ray photon. Which way does the scattered photon move? Explain your reasoning, using the principle of conservation of momentum.

| 8 | A photon can undergo Compton scattering from a molecule such as nitrogen, just as it does from an electron. However, the change in photon wavelength is much less than when the scattering is from an electron. Explain why, using Equation 29.7 for a nitrogen molecule instead of an electron.

| 9 | When the speed (assumed to be much less than the speed of light) of a particle doubles, the particle’s momentum doubles, and its kinetic energy becomes four times greater. When the momentum of a photon doubles, does its energy become four times greater? Provide a reason for your answer.

| 10 | ssm Review Conceptual Example 4 as background for this question. The photograph shows a device called a radiometer. The four rectangular panels are black on one side and shiny like a mirror on the other side. In bright light the panel arrangement spins around, in a direction from the black side of a panel toward the shiny side. Do photon collisions with both sides of the panels (collisions such as those discussed in Conceptual Example 4) cause the observed spinning? Give your reasoning.

| 11 | A stone is dropped from the top of a building. As the stone falls, does its de Broglie wavelength increase, decrease, or remain the same? Provide a reason for your answer.

| 12 | An electron and a neutron have different masses. Is it possible, according to Equation 29.8, that they can have the same de Broglie wavelength? Account for your answer.

| 13 | ssm In Figure 29-1 replace the electrons with protons that have the same speed. With the aid of Equation 27.1 for the bright fringes in Young’s double-slit experiment and Equation 29.8, decide whether the angular separation between the fringes would increase, decrease, or remain the same when compared to that produced by the electrons.

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