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physics
modern physics

Questions and Answers of Modern Physics

What voltage is needed to produce electron wavelengths of 0.26 nm? (Assume that the electrons are nonrelativistic.)
Electrons are accelerated by 2850 V in an electron microscope. Estimate the maximum possible resolution of the microscope.
For the three hydrogen transitions indicated below, with n being the initial state and being the final state, is the transition an absorption or an emission? Which is higher, the initial state energy
Estimate the peak wavelength for radiation emitted from (a) Ice at 0°C, (b) A floodlamp at 3100 K, (c) Helium at 4K, assuming blackbody emission. In what region of the EM spectrum is each?
How much energy is needed to ionize a hydrogen atom in the n = 3 state?
(a) What is the temperature if the peak of a blackbody spectrum is at 18.0 nm? (b) What is the wavelength at the peak of a blackbody spectrum if the body is at a temperature of 2200 K?
Determine the electrostatic potential energy and the kinetic energy of an electron in the ground state of the hydrogen atom.
A beam of 72-eV electrons is scattered from a crystal, as in X-ray diffraction, and a first-order peak is observed at θ = 38◦. What is the spacing between planes in the diffracting crystal?
A microwave oven produces electromagnetic radiation at λ = 12.2 cm and produces a power of 720 W. Calculate the number of microwave photons produced by the microwave oven each second.
An HCl molecule vibrates with a natural frequency of 8.1 × 1013 Hz. What is the difference in energy (in joules and electron volts) between successive values of the oscillation energy?
Sunlight reaching the Earth's atmosphere has an intensity of about 1300 W/m2. Estimate how many photons per square meter per second this represents. Take the average wavelength to be 550 nm.
A beam of red laser light (λ = 633 nm) hits a black wall and is fully absorbed. If this light exerts a total force f = 5.8 nN on the wall, how many photons per second are hitting the wall?
A flashlight emits 2.5 W of light. As the light leaves the flashlight in one direction, a reaction force is exerted on the flashlight in the opposite direction. Estimate the size of this reaction
A photomultiplier tube (a very sensitive light sensor), is based on the photoelectric effect: incident photons strike a metal surface and the resulting ejected electrons are collected. By counting
An electron and a positron collide head on, annihilate, and create two 0.85-MeV photons traveling in opposite directions. What were the initial kinetic energies of electron and positron?
By what potential difference must (a) A proton (m = 1.67 × 10-27 kg), (b) An electron (m = 9.11 × 10-31 kg), be accelerated from rest to have a wavelength λ = 4.0 × 10-12 m?
In some of Rutherford's experiments (Fig. 27-19) the α particles (mass = 6.64 × 10-27 kg) had a kinetic energy of 4.8 MeV. How close could they get to the surface of a gold nucleus (radius = 7.0 ×
The steps of a flight of stairs are 20.0 cm high (vertically). If a 62.0-kg person stands with both feet on the same step, what is the gravitational potential energy of this person, relative to the
Electrons accelerated from rest by a potential difference of 12.3 V pass through a gas of hydrogen atoms at room temperature. What wavelengths of light will be emitted?
In a particular photoelectric experiment, a stopping potential of 2.10 V is measured when ultraviolet light of wavelength 270 nm is incident on the metal. Using the same setup, what will the new
Neutrons can be used in diffraction experiments to probe the lattice structure of crystalline solids. Since the neutron's wavelength needs to be on the order of the spacing between atoms in the
In Chapter 22, the intensity of light striking a surface was related to the electric field of the associated electromagnetic wave. For photons, the intensity is the number of photons striking a 1-m2
The intensity of the Sun's light in the vicinity of the Earth is about 1350 W/m2. Imagine a spacecraft with a mirrored square sail of dimension 1.0 km. Estimate how much thrust (in newtons) this
Light of wavelength 280 nm strikes a metal whose work function is 2.2 eV. What is the shortest de Broglie wavelength for the electrons that are produced as photoelectrons?
What would be the theoretical limit of resolution for an electron microscope whose electrons are accelerated through 110 kV? (Relativistic formulas should be used.)
Assume hydrogen atoms in a gas are initially in their ground state. If free electrons with kinetic energy 12.75 eV collide with these atoms, what photon wavelengths will be emitted by the gas?
Visible light incident on a diffraction grating with slit spacing of 0.010 mm has the first maximum at an angle of 3.6° from the central peak. If electrons could be diffracted by the same grating,
Estimate the peak wavelength of light emitted from the pupil of the human eye (which approximates a blackbody) assuming normal body temperature.
(a) Suppose an unknown element has an absorption spectrum with lines corresponding to 2.5, 4.7, and 5.1 eV above its ground state and an ionization energy of 11.5 eV. Draw an energy level diagram for
A photon of momentum 3.53 × 10-28 kg · m/s is emitted from a hydrogen atom. To what spectrum series does this photon belong, and from what energy level was it ejected?
Light of wavelength 464 nm falls on a metal which has a work function of 2.28 eV. (a) How much voltage should be applied to bring the current to zero? (b) What is the maximum speed of the emitted
At what temperature would the average kinetic energy (Chapter 13) of a molecule of hydrogen gas (H2) be sufficient to excite a hydrogen atom out of the ground state?
State the principle of complementarity, and give at least two experimental results that support this principle for electrons and for photons.
Imagine the following Young's double-slit experiment using matter rather than light: electrons are accelerated through a potential difference of 12 V pass through two closely spaced slits separated
(a) From Sections 22-3, 24-4, and 27-3, estimate the minimum energy (eV) that initiates the chemical process on the retina responsible for vision. (b) Estimate the threshold photon energy above
(a) A rubidium atom (m = 85u) is at rest with one electron in an excited energy level. When the electron jumps to the ground state, the atom emits a photon of wavelength λ = 780 nm. Determine the
Suppose a particle of mass m is confined to a one-dimensional box of width L. According to quantum theory, the particle's wave (with λ = h/mv) is a standing wave with nodes at the edges of the
Excited hydrogen and excited helium atoms both radiate light as they jump down to the n = 1, ℓ = 0, mℓ = 0 state. Why do the two elements have very different emission spectra?
Why are the chemical properties of the rare earths so similar?
Does the Bohr model of the atom violate the uncertainty principle? Explain.
Briefly explain why noble gases are nonreactive and why alkali metals are highly reactive.
1. An atom has the electron configuration How many electrons does this atom have? (a) 15. (b) 19. (c) 30. (d) 46. 2. For the electron configuration of MisConceptual Question 1, what orbital
1. What is meant by the ground state of an atom? (a) All of the quantum numbers have their lowest values (n = 1, ℓ = mℓ = 0). (b) The principal quantum number of the electrons in the outer shell
1. Which of the following is the best paraphrasing of the Heisenberg uncertainty principle? (a) Only if you know the exact position of a particle can you know the exact momentum of the particle. (b)
1. According to the uncertainty principle,(a) There is always an uncertainty in a measurement of the position of a particle.(b) There is always an uncertainty in a measurement of the momentum of a
The neutrons in a parallel beam, each having kinetic energy 0.025 eV, are directed through two slits 0.40 mm apart. How far apart will the interference peaks be on a screen 1.0 m away?
A radioactive element undergoes an alpha decay with a lifetime of 12 μs. If alpha particles are emitted with 5.5-MeV kinetic energy, find the percent uncertainty E/E in the particle energy.
If an electron's position can be measured to a precision of 15 nm, what is the uncertainty in its speed? Assuming the minimum speed must be at least equal to its uncertainty, what is the electron's
Estimate the lowest possible energy of a neutron contained in a typical nucleus of radius 1.2 × 10-15m.
How precisely can the position of a 5.00-keV electron be measured assuming its energy is known to 1.00%?
Use the uncertainty principle to show that if an electron were present in the nucleus (r ≈ 10-15m), its kinetic energy (use relativity) would be hundreds of MeV. (Since such electron energies are
For n = 6, ℓ = 3, what are the possible values of mℓ and ms?
How many electrons can be in the n = 5, ℓ = 3 subshell?
List the quantum numbers for each electron in the ground state of(a) Carbon (Z = 6),(b) Aluminum (Z = 13).
Pellets of mass 2.0 g are fired in parallel paths with speeds of 120 m/s through a hole 3.0 mm in diameter. How far from the hole must you be to detect a 1.0-cmdiameter spread in the beam of pellets?
List the quantum numbers for each electron in the ground state of oxygen (Z = 8).
Calculate the magnitude of the angular momentum of an electron in the n = 5, ℓ = 3 state of hydrogen.
If a hydrogen atom has ℓ = 4, what are the possible values for n, mℓ, and ms?
If a hydrogen atom has mℓ = - 3, what are the possible values of n, ℓ, and ms?
What is the full electron configuration in the ground state for elements with Z equal to (a) 26, (b) 34, (c) 38?
What is the full electron configuration for(a) Silver (Ag),(b) Gold (Au),(c) Uranium (U)?
A hydrogen atom is in the 5d state. Determine(a) The principal quantum number,(b) The energy of the state,(c) The orbital angular momentum and its quantum number and(d) The possible values for the
For each of the following atomic transitions, state whether the transition is allowed or forbidden, and why:(a) 4p → 3p;(b) 3p → 1s;(c) 4d → 2d;(d) 5d → 3s;(e) 4s → 2p;
What are the shortest-wavelength X-rays emitted by electrons striking the face of a 28.5-kV TV picture tube? What are the longest wavelengths?
If the shortest-wavelength bremsstrahlung X-rays emitted from an X-ray tube have λ = 0.035nm, what is the voltage across the tube?
Estimate the wavelength for an n = 3 to n = 2 transition in iron (Z = 26).
Use the Bohr model to estimate the wavelength for an n = 3 to n = 1 transition in molybdenum (Z = 42). The measured value is 0.063 nm. Why do we not expect perfect agreement?
If an electron's position can be measured to a precision of 2.4 × 10-8 m, how precisely can its speed be known?
A laser used to weld detached retinas puts out 25-ms-long pulses of 640-nm light which average 0.68-W output during a pulse. How much energy can be deposited per pulse and how many photons does each
A low-power laser used in a physics lab might have a power of 0.50 mW and a beam diameter of 3.0 mm. Calculate (a) The average light intensity of the laser beam, and (b) Compare it to the intensity
Calculate the wavelength of the He-Ne laser (see Fig. 28-20).
Estimate the angular spread of a laser beam due to diffraction if the beam emerges through a 3.0-mm-diameter mirror. Assume that λ = 694 nm. What would be the diameter of this beam if it struck?(a)
An electron in the n = 2 state of hydrogen remains there on average about 10-8s before jumping to the n = 1 state. (a) Estimate the uncertainty in the energy of the n = 2 state. (b) What fraction of
What are the largest and smallest possible values for the angular momentum L of an electron in the n = 6 shell?
An electron remains in an excited state of an atom for typically 10-8s. What is the minimum uncertainty in the energy of the state (in eV)?
The ionization (binding) energy of the outermost electron in boron is 8.26 eV.(a) Use the Bohr model to estimate the "effective charge," Zeff, seen by this electron.(b) Estimate the average orbital
Protons are accelerated from rest across 480 V. They are then directed at two slits 0.70 mm apart. How far apart will the interference peaks be on a screen 28 m away?
How many electrons can there be in an "h" subshell?
A beam of electrons with kinetic energy 45 keV is shot through two narrow slits in a barrier. The slits are a distance 2.0 × 10-6 m apart. If a screen is placed 45.0 cm behind the barrier, calculate
The lifetime of a typical excited state in an atom is about 10 ns. Suppose an atom falls from one such excited state to a lower one, and emits a photon of wavelength about 500 nm. Find the fractional
A 1300-kg car is traveling with a speed of (22 ± 0.22) m/s. With what maximum precision can its position be determined?
The Z0 boson, discovered in 1985, is the mediator of the weak nuclear force, and it typically decays very quickly. Its average rest energy is 91.19 GeV, but its short lifetime shows up as an
An atomic spectrum contains a line with a wavelength centered at 488 nm. Careful measurements show the line is really spread out between 487 and 489 nm. Estimate the lifetime of the excited state
If your de Broglie wavelength were 0.50 m, how fast would you be moving if your mass is 68.0 kg? Would you notice diffraction effects as you walk through a doorway? Approximately how long would it
Photons of wavelength 0.154 nm are emitted from the surface of a certain metal when it is bombarded with highenergy radiation. If this photon wavelength corresponds to the K line, what is the element?
What is the uncertainty in the mass of a muon (m = 105.7MeV/c2), specified eV/e2, in given its lifetime of 2.20 μs?
A free neutron (m = 1.67 × 10-27 kg) has a mean life of 880 s. What is the uncertainty in its mass (in kg)?
An electron and a 140-g baseball are each traveling 120 m/s measured to a precision of 0.065%. Calculate and compare the uncertainty in position of each.
On what factors does the periodicity of the Periodic Table depend? Consider the exclusion principle, quantization of angular momentum, spin, and any others you can think of.
What is the main difference between n-type and p-type semiconductors?
1. What holds molecules together? (a) Gravitational forces. (b) Magnetic forces. (c) Electric forces. (d) Glue. (e) Nuclear forces. 2. Which of the following is true for covalently bound diatomic
1. A hydrogen atom (Z = 1) is bonded to a lithium atom in lithium hydride, LiH. Which of the following are possible spin states of the two shared electrons? (a) + ½, + ½. (b) - ½, - ½. (c) + ½,
Consider Fig. 29-10. As the last phosphate group approaches and then bonds to the ADP molecule, which of the following is true? Choose all that apply. (a) The phosphate group is first repelled and
1. Which type of bond holds the molecules of the DNA double helix together? (a) Covalent bond. (b) Ionic bond. (c) Einstein bond. (d) Van der Waals bond. 2. In a p-type semiconductor, a hole is (a)
1. Which of the following would not be used as an impurity in doping silicon? (a) Germanium. (b) Gallium. (c) Boron. (d) Phosphorus. (e) Arsenic. 2. Why are metals good conductors? (a) Gaining a tiny
Estimate the binding energy of a KCl molecule by calculating the electrostatic potential energy when the K+ and CI- ions are at their stable separation of 0.28 nm. Assume each has a charge of
Determine the wavelength of the photon emitted when the CO molecule makes the rotational transition ℓ = 5 to ℓ = 4.
Calculate the bond length for the NaCl molecule given that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and 7.71 mm.
Repeat Problem 14 for KCl whose density is 1.99 g/cm3. In Repeat Problem 14 Common salt, NaCl, has a density of 2.165g/cm3. The molecular weight of NaCl is 58.44. Estimate the distance between
A semiconductor is struck by light of slowly increasing frequency and begins to conduct when the wavelength of the light is 620 nm. Estimate the energy gap Eg.

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