Unreasonable Results A student in a physics laboratory observes a hydrogen spectrum with a diffraction grating for the purpose of measuring the wavelengths of the emitted radiation . In the spectrum, she observes a yellow line and finds its wavelength to be 589 nm. (a) Assuming this is part of the Balmer series, determine n i , the principal quantum number of the initial state. (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?
Unreasonable Results A student in a physics laboratory observes a hydrogen spectrum with a diffraction grating for the purpose of measuring the wavelengths of the emitted radiation . In the spectrum, she observes a yellow line and finds its wavelength to be 589 nm. (a) Assuming this is part of the Balmer series, determine n i , the principal quantum number of the initial state. (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?
A student in a physics laboratory observes a hydrogen spectrum with a diffraction grating for the purpose of measuring the wavelengths of the emitted radiation. In the spectrum, she observes a yellow line and finds its wavelength to be 589 nm. (a) Assuming this is part of the Balmer series, determine
n
i
, the principal quantum number of the initial state. (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?
3:09 O O O 63° A X •
N N O 5G „ll
Quizzes
a
(absorption)
Brackett
series
Paschen
series
Lyman
series
(emission)
Balmer series
Paschen
series
(emission)
n= 2
n=3
n=4
....
Lyman series
n-5
(a)
(b)
e These pictures refer to the energy levels
of a hydrogen atom.
You can find the error in both parts, (a) and
(b). The arrows labeled "emission" in (a), and
all the arrows in (b), indicate a transition in
which an electron jumps from a higher-
energy state to a lower-energy state. The
different "series" of emission lines are
characterized by the index n of the low-
energy state in which the electron ends up.
In particular, the Lyman series consists of all
transitions that end up in the n=1 energy
level, with an initial energy level that
corresponds to the label n = 2, 3, 4, 5, etc.
One of these values of n is not shown as an
arrow in the Lyman emission series in figures
(a) or (b). This is a significant error because
that particular spectral line is very important
in astronomy.
Pick the value…
a) An electron in a hydrogen atom has energy E= -3.40 eV, where the zero of energy is at the
ionization threshold. In the Bohr model, what is the angular momentum of the electron? Express your
result as a multiple of ħ.
Ans.
b) What is the deBroglie wavelength of the electron when it is in this state? Ans.
c) When the electron is in this state, what is the ratio of the circumference of the orbit of the electron
to the deBroglie wavelength of the electron?
Ans.
d) The electron makes a transition from the state with energy E= -3.40 eV to the ground state, that
has energy -13.6 eV. What is the wavelength of the photon emitted during this transition?
Ans.
An electron is in the nth Bohr orbit of the hydrogen atom.
n3
(a) Show that the period of the electron is T = to n³ and determine the numerical value of to.
153
as
(b) On average, an electron remains in the n = 2 orbit for approximately 8 us before it jumps down to the n = 1
(ground-state)orbit. How many revolutions does the electron make in the excited state?
8.26e+09
×
(c) Define the period of one revolution as an electron year, analogous to an Earth year being the period of the
Earth's motion around the Sun. Explain whether we should think of the electron in the n = 2 orbit as "living for a
long time."
Physics for Scientists and Engineers: A Strategic Approach, Vol. 1 (Chs 1-21) (4th Edition)
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