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a. A negatively charged electroscope can be discharged by shining an ultraviolet light on it. How does this happen?

b. You might think that an ultraviolet light shining on an initially uncharged electroscope would cause the electroscope to become positively charged as photoelectrons are emitted. In fact, ultraviolet light has no noticeable effect on an uncharged electroscope. Why not?

Which metals in Table 38.1 exhibit the photoelectric effect for (a) light with$\mathrm{λ}=400\mathrm{nm}$ and (b) light with $\mathrm{λ}=250\mathrm{nm}$?

An FM radio station broadcasts with a power of 10 kW at a frequency of 101 MHz.

a. How many photons does the antenna emit each second?

b. Should the broadcast be treated as an electromagnetic wave or discrete photons? Explain.

If an electron is in a stationary state of an atom, is the electron at rest? If not, what does the term mean?

FIGURE Q38.12 shows the energy-level diagram of Element X.

a. What is the ionization energy of Element X?

b. An atom in the ground state absorbs a photon, then emits a photon with a wavelength of 1240 nm. What was the energy of the photon that was absorbed?

c. An atom in the ground state has a collision with an electron, then emits a photon with a wavelength of 1240 nm. What conclusion can you draw about the initial kinetic energy of the electron?

For what wavelength of light does a 100 mW laser deliver $2.50×{10}^{17}$photons per second?

Draw an energy-level diagram, similar to Figure 38.21, for the ${\mathrm{He}}^{+}$ion. On your diagram:

a. Show the first five energy levels. Label each with the values of n and${\mathrm{E}}_{\mathrm{n}}$

b. Show the ionization limit.

c. Show all possible emission transitions from the n = 4 energy level.

d. Calculate the wavelengths (in nm) for each of the transitions in part c and show them alongside the appropriate arrow.

A 100 W incandescent lightbulb emits about 5 W of visible light. (The other 95 W are emitted as infrared radiation or lost as heat to the surroundings.) The average wavelength of the visible light is about 600 nm, so make the simplifying assumption that all the light has this wavelength. How many visible-light photons does the bulb emit per second?

A 100 W incandescent lightbulb emits about 5 W of visible light. (The other 95 W are emitted as infrared radiation or lost as heat to the surroundings.) The average wavelength of the visible light is about 600 nm, so make the simplifying assumption that all the light has this wavelength. How many visible-light photons does the bulb emit per second?

What is the energy, in keV, of 75 keV x-ray photons that are backscattered (i.e., scattered directly back toward the source) by the electrons in a target?