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1			In the photoelectric effect, why are no electrons emitted from the metal when the incident light is below the threshold frequency?
2			A darkroom used for developing black-and-white film can be dimly lit by a red lightbulb without ruining the film. Why is a red lightbulb used rather than white or blue or some other color?
3			A fluorescent substance absorbs EM radiation of one wavelength and then emits EM radiation of a different wavelength. Which wavelength is longer? Explain.
4			Find the (a) wavelength and (b) frequency of a 3.1-eV photon.
5			A rubidium surface has a work function of 2.16 eV. (a) What is the maximum kinetic energy of ejected electrons if the incident radiation is of wavelength 413 nm? (b) What is the threshold wavelength for this surface?
6			The minimum energy required to remove an electron from a metal is 2.60 eV. What is the longest wavelength photon that can eject an electron from this metal?
7			What is the cutoff frequency for an x-ray tube operating at 46 kV?
8			X-rays of wavelength 10.0 pm are incident on a target. Find the wavelengths of the x-rays scattered at (a) 45.0° and (b) 90.0°.
9			Find the energy for a hydrogen atom in the stationary state n = 4.
10			A hydrogen atom in its ground state absorbs a photon of energy 12.1 eV. To what energy level is the atom excited?
11			How much energy is required to remove an electron from a hydrogen atom in the n = 4 state?
12			Nuclei in a radium-226 radioactive source emit photons whose energy is 186 keV. These photons are scattered by the electrons in a metal target; a detector measures the energy of the scattered photons as a function of the angle θ through which they are scattered. Find the energy of the scattered γ-rays scattered through θ = 90.0° and 180.0°.