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University Physics III · unit UPIII-10

Atomic Physics

Connect the ideas, make your working visible, and test the result. Use the hints when you need a starting point; open the full solution after your attempt.

Extra challenging questions

A selection from this pathway. Open a topic below for its complete practice and challenge set.

Extra challenging · 01

Atomic spectra and quantised energy levels: infer an input with uncertainty

An atomic line spectrum is the set of sharp wavelengths an atom emits or absorbs; each line's photon energy hf equals the difference between two of the atom's allowed energy levels, so the spectrum is a map of level differences. Use the supplied topic model Y_out = 13.598*(1/n1^2 - 1/(n1+k)^2), where Y_out is PHOTON ENERGY hf (eV). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793. n1 is Lower level n₁ (series), dimensionless. Keep k (Upper level above it, n₂ − n₁) = 1 fixed. For this exercise use only 1 ≤ n1 ≤ 3, at the specified test settings separated by 1. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. A reading gives Y_out = 1.8886111 eV, with a bounded reading uncertainty ±0.763 eV. Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. Determine every allowed value of n1 consistent with that bound. Compare with a straight-line interpolation between the two endpoint predictions, and explain why a fractional setting may be inadmissible. Do not assume that the supplied calibration points prove monotonicity outside this branch.

Explore the question data

PHOTON ENERGY hf against n1

Predictions from the supplied Atomic spectra and quantised energy levels model, with all other inputs fixed as stated in the question. 3 calibration points support a trend comparison; they are not measured data or a straight-line law.

Vertical axis (y): PHOTON ENERGY hf / eV

PHOTON ENERGY hf against n1Predictions from the supplied Atomic spectra and quantised energy levels model, with all other inputs fixed as stated in the question. 3 calibration points support a trend comparison; they are not measured data or a straight-line law. Horizontal axis: n1: Lower level n₁ (series). Vertical axis: PHOTON ENERGY hf / eV. Exact values are available in the data table below.0.27952.8555.438.00510.580.921.4622.543.08xy

Horizontal axis (x): n1: Lower level n₁ (series)

Axes show the supplied calibration interval; the origin may lie outside the plot.

Reading 1n1: Lower level n₁ (series): 1PHOTON ENERGY hf / eV: 10.2
Read the exact data as a table
PHOTON ENERGY hf against n1 — supplied values
n1: Lower level n₁ (series)PHOTON ENERGY hf / eV
110.198500000000001
21.8886111111111112
30.6610138888888888

These are the supplied values, not a worked answer. No fitted trend is drawn.

Show a hint

Enumerate the permitted settings in the stated range, evaluate Y_out at each, and retain every setting satisfying |Y_out − Y_measured| ≤ u. The plotted predictions are supplied calibration evidence.

Reveal the worked solution
  1. Endpoint predictions are Y_out(1) = 10.1985 eV and Y_out(3) = 0.661014 eV. The target lies between them. On the selected branch the response is strictly decreasing.
  2. Endpoint interpolation gives n1_line = 1 + (1.88861 − 10.1985)(3 − 1)/(0.661014 − 10.1985) = 2.74257. This estimates the inverse of the endpoint chord, rather than assuming that chord is the physical model.
  3. Evaluate the model at each permitted setting. The central reading corresponds to n1 = 2; only the allowed settings 2 lie inside the stated reading bound.
  4. The interpolation error in the input is |n1_line − n1| = 0.742574.
  5. The compatible allowed values span 2 to 2. Values between specified test settings are outside this exercise's input domain even if an interpolation passes through them.
  6. The quoted output bound restricts which specified settings remain compatible. It does not change physical restrictions on quantum numbers or counts, and the chosen grid alone does not establish physical quantisation.

Answer Compatible n1: 2. Endpoint interpolation predicts 2.74257; check admissibility against the discrete settings.

Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.

Extra challenging · 02

The Bohr model and its failures: infer an input with uncertainty

The Bohr model treats a one-electron atom as an electron on a classical circular Coulomb orbit whose angular momentum is restricted to whole multiples of ħ, emitting or absorbing light only when it jumps between those orbits. Use the supplied topic model Y_out = -13.6*z/r, where Y_out is ORBIT ENERGY E (eV). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793. r is Orbit radius r, measured in a₀. Keep z (Nuclear charge Z) = 1 fixed. For this exercise use only 1.92344 a₀ ≤ r ≤ 14.3266 a₀ on this continuous branch. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. A reading gives Y_out = -1.4331866 eV, with a bounded reading uncertainty ±0.072585 eV. Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. First estimate the unknown r by straight-line interpolation between the two endpoint predictions. Then solve the actual model on the stated branch to an absolute input tolerance of 0.00124031 a₀, using a numerical bracket if required. Find the full input interval consistent with the bounded reading uncertainty and compare it with a symmetric input-error assumption. Do not assume that the supplied calibration points prove monotonicity outside this branch.

Explore the question data

ORBIT ENERGY E against r

Predictions from the supplied The Bohr model and its failures model, with all other inputs fixed as stated in the question. 5 calibration points support a trend comparison; they are not measured data or a straight-line law.

Vertical axis (y): ORBIT ENERGY E / eV

ORBIT ENERGY E against rPredictions from the supplied The Bohr model and its failures model, with all other inputs fixed as stated in the question. 5 calibration points support a trend comparison; they are not measured data or a straight-line law. Horizontal axis: r: Orbit radius r / a₀. Vertical axis: ORBIT ENERGY E / eV. Exact values are available in the data table below.-7.316-5.663-4.01-2.357-0.70441.4274.7768.12511.4714.82xy

Horizontal axis (x): r: Orbit radius r / a₀

Axes show the supplied calibration interval; the origin may lie outside the plot.

Reading 1r: Orbit radius r / a₀: 1.923ORBIT ENERGY E / eV: -7.071
Read the exact data as a table
ORBIT ENERGY E against r — supplied values
r: Orbit radius r / a₀ORBIT ENERGY E / eV
1.9234375-7.070674248578392
5.024218749999999-2.7068885087855703
8.125-1.6738461538461538
11.225781249999999-1.2114969726494538
14.3265625-0.9492856363834661

These are the supplied values, not a worked answer. No fitted trend is drawn.

Show a hint

The model's endpoint predictions bracket the reading. Solve Y_out(r) = Y_measured and then solve again at Y_measured − u and Y_measured + u; a nonlinear inverse can give unequal input deviations.

Reveal the worked solution
  1. Endpoint predictions are Y_out(1.92344) = -7.07067 eV and Y_out(14.3266) = -0.949286 eV. The target lies between them. On the selected branch the response is strictly increasing.
  2. Endpoint interpolation gives r_line = 1.92344 + (-1.43319 − -7.07067)(14.3266 − 1.92344)/(-0.949286 − -7.07067) = 13.3461 a₀. This estimates the inverse of the endpoint chord, rather than assuming that chord is the physical model.
  3. Use the actual equation, not the chord, and bracket its root. Evaluating the midpoint and retaining the sign-changing half-interval gives r = 9.48934 a₀; substituting back gives Y_out = -1.4331866 eV.
  4. The interpolation error in the input is |r_line − r| = 3.85674 a₀. This is larger than the requested numerical tolerance.
  5. Invert both limits Y_out = -1.5057716 eV and -1.3606016 eV. Sort the roots even if the response decreases: 9.03191 a₀ ≤ r ≤ 9.99558 a₀.
  6. The lower and upper input deviations are 0.457429 a₀ and 0.506235 a₀. They differ because the inverse response is nonlinear; a symmetric error bar would only be a local approximation. This interval includes reading uncertainty only, not model error or uncertainty in fixed inputs.

Answer r ≈ 9.48934 a₀; compatible interval [9.03191, 9.99558] a₀. Endpoint interpolation gives 13.3461 a₀.

Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.

Extra challenging · 03

The Schrödinger equation for the Coulomb potential: infer an input with uncertainty

The Coulomb-potential Schrödinger equation describes one electron bound by −ke²/r to a fixed point nucleus; separated in spherical coordinates, it has normalisable solutions only for integer m, l and n, with the energy set by n alone. Use the supplied topic model Y_out = -13.606/n^2, where Y_out is LEVEL Eₙ = −13.6 eV/n² (eV). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793. n is Principal quantum number n, dimensionless. Keep l (Orbital quantum number l) = 1 fixed. For this exercise use only 2 ≤ n ≤ 4, at the specified test settings separated by 1. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. A reading gives Y_out = -1.5117778 eV, with a bounded reading uncertainty ±0.20409 eV. Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. Determine every allowed value of n consistent with that bound. Compare with a straight-line interpolation between the two endpoint predictions, and explain why a fractional setting may be inadmissible. Do not assume that the supplied calibration points prove monotonicity outside this branch.

Explore the question data

LEVEL Eₙ = −13.6 eV/n² against n

Predictions from the supplied The Schrödinger equation for the Coulomb potential model, with all other inputs fixed as stated in the question. 3 calibration points support a trend comparison; they are not measured data or a straight-line law.

Vertical axis (y): LEVEL Eₙ = −13.6 eV/n² / eV

LEVEL Eₙ = −13.6 eV/n² against nPredictions from the supplied The Schrödinger equation for the Coulomb potential model, with all other inputs fixed as stated in the question. 3 calibration points support a trend comparison; they are not measured data or a straight-line law. Horizontal axis: n: Principal quantum number n. Vertical axis: LEVEL Eₙ = −13.6 eV/n² / eV. Exact values are available in the data table below.-3.504-2.815-2.126-1.437-0.74831.922.4633.544.08xy

Horizontal axis (x): n: Principal quantum number n

Axes show the supplied calibration interval; the origin may lie outside the plot.

Reading 1n: Principal quantum number n: 2LEVEL Eₙ = −13.6 eV/n² / eV: -3.401
Read the exact data as a table
LEVEL Eₙ = −13.6 eV/n² against n — supplied values
n: Principal quantum number nLEVEL Eₙ = −13.6 eV/n² / eV
2-3.4015
3-1.5117777777777777
4-0.850375

These are the supplied values, not a worked answer. No fitted trend is drawn.

Show a hint

Enumerate the permitted settings in the stated range, evaluate Y_out at each, and retain every setting satisfying |Y_out − Y_measured| ≤ u. The plotted predictions are supplied calibration evidence.

Reveal the worked solution
  1. Endpoint predictions are Y_out(2) = -3.4015 eV and Y_out(4) = -0.850375 eV. The target lies between them. On the selected branch the response is strictly increasing.
  2. Endpoint interpolation gives n_line = 2 + (-1.51178 − -3.4015)(4 − 2)/(-0.850375 − -3.4015) = 3.48148. This estimates the inverse of the endpoint chord, rather than assuming that chord is the physical model.
  3. Evaluate the model at each permitted setting. The central reading corresponds to n = 3; only the allowed settings 3 lie inside the stated reading bound.
  4. The interpolation error in the input is |n_line − n| = 0.481481.
  5. The compatible allowed values span 3 to 3. Values between specified test settings are outside this exercise's input domain even if an interpolation passes through them.
  6. The quoted output bound restricts which specified settings remain compatible. It does not change physical restrictions on quantum numbers or counts, and the chosen grid alone does not establish physical quantisation.

Answer Compatible n: 3. Endpoint interpolation predicts 3.48148; check admissibility against the discrete settings.

Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.

Extra challenging · 04

Orbital angular momentum and spherical harmonics: infer an input with uncertainty

Quantum orbital angular momentum has a sharp magnitude √(l(l+1)) ħ and a sharp component mħ along one chosen axis, with l = 0, 1, 2, … and m = −l, …, +l; the angular wavefunctions carrying these values are the spherical harmonics Yₗₘ(θ, φ). Use the supplied topic model Y_out = (l*(l+1)-clamp(m,-l,l)^2)/2, where Y_out is ΔLₓ ΔL_y (ħ²). The output symbol Y_out is distinct from all input symbols. ^ denotes a power; π = 3.141592653589793; clamp(x,a,b) confines x to [a,b]. m is Magnetic number m, held to |m| ≤ l, dimensionless. Keep l (Orbital quantum number l) = 2 fixed. For this exercise use only -2 ≤ m ≤ 0, at the specified test settings separated by 1. A grid of test settings is an input restriction for this exercise, not by itself a claim of physical quantisation. This calculation retains the topic model's stated assumptions; it does not extend them to a different physical setup. A reading gives Y_out = 2.5 ħ², with a bounded reading uncertainty ±0.16 ħ². Treat the model and all fixed inputs as exact for this exercise; the bound is not a standard deviation. Determine every allowed value of m consistent with that bound. Compare with a straight-line interpolation between the two endpoint predictions, and explain why a fractional setting may be inadmissible. Do not assume that the supplied calibration points prove monotonicity outside this branch.

Explore the question data

ΔLₓ ΔL_y against m

Predictions from the supplied Orbital angular momentum and spherical harmonics model, with all other inputs fixed as stated in the question. 3 calibration points support a trend comparison; they are not measured data or a straight-line law.

Vertical axis (y): ΔLₓ ΔL_y / ħ²

ΔLₓ ΔL_y against mPredictions from the supplied Orbital angular momentum and spherical harmonics model, with all other inputs fixed as stated in the question. 3 calibration points support a trend comparison; they are not measured data or a straight-line law. Horizontal axis: m: Magnetic number m, held to |m| ≤ l. Vertical axis: ΔLₓ ΔL_y / ħ². Exact values are available in the data table below.0.921.4622.543.08-2.08-1.54-1-0.460.08xy

Horizontal axis (x): m: Magnetic number m, held to |m| ≤ l

Axes show the supplied calibration interval; the origin may lie outside the plot.

Reading 1m: Magnetic number m, held to |m| ≤ l: -2ΔLₓ ΔL_y / ħ²: 1
Read the exact data as a table
ΔLₓ ΔL_y against m — supplied values
m: Magnetic number m, held to |m| ≤ lΔLₓ ΔL_y / ħ²
-21
-12.5
03

These are the supplied values, not a worked answer. No fitted trend is drawn.

Show a hint

Enumerate the permitted settings in the stated range, evaluate Y_out at each, and retain every setting satisfying |Y_out − Y_measured| ≤ u. The plotted predictions are supplied calibration evidence.

Reveal the worked solution
  1. Endpoint predictions are Y_out(-2) = 1 ħ² and Y_out(0) = 3 ħ². The target lies between them. On the selected branch the response is strictly increasing.
  2. Endpoint interpolation gives m_line = -2 + (2.5 − 1)(0 − -2)/(3 − 1) = -0.5. This estimates the inverse of the endpoint chord, rather than assuming that chord is the physical model.
  3. Evaluate the model at each permitted setting. The central reading corresponds to m = -1; only the allowed settings -1 lie inside the stated reading bound.
  4. The interpolation error in the input is |m_line − m| = 0.5.
  5. The compatible allowed values span -1 to -1. Values between specified test settings are outside this exercise's input domain even if an interpolation passes through them.
  6. The quoted output bound restricts which specified settings remain compatible. It does not change physical restrictions on quantum numbers or counts, and the chosen grid alone does not establish physical quantisation.

Answer Compatible m: -1. Endpoint interpolation predicts -0.5; check admissibility against the discrete settings.

Compare the assumptions, method and units with your attempt. Explain any correction before trying another question.

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