Problem 74
The photoelectric effect is studied using a tungsten target. The work function
of tungsten is 4.5 eV. The incident photons have energy \(4.8 \mathrm{eV} .\)
(a) What is the threshold frequency?
(b) What is the stopping potential?
(c) Explain why, in classical physics, no threshold frequency is expected.
Problem 75
An x-ray photon with wavelength 6.00 pm collides with a free electron
initially at rest. What is the maximum possible kinetic energy acquired by the
electron?
Problem 76
A photoelectric effect experiment is performed with tungsten. The work
function for tungsten is 4.5 eV.
(a) If ultraviolet light of wavelength \(0.20 \mu \mathrm{m}\) is incident on
the tungsten, calculate the stopping potential.
(b) If the stopping potential is turned off (i.e., the cathode and anode are
at the same voltage), the \(0.20-\mu \mathrm{m}\) incident light produces a
photocurrent of \(3.7 \mu \mathrm{A} .\) What is the photocurrent if the
incident light has wavelength \(400 \mathrm{nm}\) and the same intensity as
before?
Problem 77
In a CRT television, electrons of kinetic energy \(2.0 \mathrm{keV}\) strike the
screen. No EM radiation is emitted below a certain wavelength. Calculate this
wavelength.
Problem 79
Consider the emission spectrum of singly ionized helium (He^). Find the
longest three wavelengths for the series in which the electron makes a
transition from a higher excited state to the first excited state (not the
ground state).
Problem 82
A hydrogen atom in its ground state is immersed in a continuous spectrum of
ultraviolet light with wavelengths ranging from 96 nm to 110 nm. After
absorbing a photon, the atom emits one or more photons to return to the ground
state. (a) What wavelength(s) can be absorbed by the \(\mathrm{H}\) atom? (b)
For each of the possibilities in (a), if the atom is at rest before absorbing
the UV photon, what is its recoil speed after absorption (but before emitting
any photons)? (c) For each of the possibilities in (a), how many different
ways are there for the atom to return to the ground state?
Problem 84
Photons of energy \(E=4.000 \mathrm{keV}\) undergo Compton scattering. What is
the largest possible change in photon energy, measured as a fraction of the
incident photon's energy \(\left(E-E^{\prime}\right) / E ?\)
Problem 85
Suppose that you have a glass tube filled with atomic hydrogen gas (H, not
\(\mathrm{H}_{2}\) ). Assume that the atoms start out in their ground states.
You illuminate the gas with monochromatic light of various wavelengths,
ranging through the entire IR, visible, and UV parts of the spectrum. At some
wavelengths, visible light is emitted from the \(\mathrm{H}\) atoms. (a) If
there are two and only two visible wavelengths in the emitted light, what is
the wavelength of the incident radiation? (b) What is the largest wavelength
of incident radiation that causes the \(\mathrm{H}\) atoms to emit visible
light? What wavelength(s) is/are emitted for incident radiation at that
wavelength? (c) For what wavelengths of incident light are hydrogen ions
\(\left(\mathrm{H}^{+}\right)\) formed?
