lots of lectures. Class is now over.

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othocaes 2016-04-28 16:51:34 -04:00
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Exam 2 Problem 2
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
(pic) Finished the problem using the boundary conditions
boundary conditions limit the number of possible spherical harmonics.
Two Similar Particles
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
❙a,b❭ = ❙a❭⊗❙b❭
Exchange Operator
──────────────────────────────────────────────────────────────────────────
𝓟₁₂❙a,b❭ = ❙a,b❭
𝓟₁₂(❙a❭⊗❙b❭) = ❙b❭⊗❙a❭
If particles are indistinguishable
𝓟₁₂❙a,b❭ = exp(iδ) ❙a,b❭ = λ ❙a,b❭
𝓟²₁₂❙a,b❭ = λ² ❙a,b❭ = ❙a,b❭ ⇒ λ=±1
Symmetry States
──────────────────────────────────────────────────────────────────────────
(pic) Two cases: symmetric, antisymmetric
Symmetric States, λ=1
𝓟₁₂❙a,b❭
(pic) Constructed the exchange operator in matrix form, then found eigen states
(pic) Showed that the exchange operator leads to the Pauli Exclusion Principle

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Two Spin-½ Particles
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
uncoupled basis
───────────────
❙s₁ s₂ m₁ m₂❭
❙+ +❭, ❙- -❭, ❙+ -❭, ❙- +❭
coupled basis
─────────────
❙S Mₛ❭
❙1 1❭, ❙1 -1❭, ❙1 0❭, ❙0 0❭
Given the state ❙1 0❭ = 1/√2(❙+ -❭ + ❙- +❭) :
P₁₂❙1 0❭ = ❙1 0❭ (symmetric)
❙0 0❭ = 1/√2(❙+ -❭ - ❙- +❭) :
P₁₂❙0 0❭ = -❙0 0❭ (antisymmetric)
Spatial Representation
──────────────────────────────────────────────────────────────────────────
❙Ψ❭ = ❙Ψₛₚₐₜᵢₐₗ❭❙Ψₛₚᵢₙ❭
Symmetric:
❙Ψ❭ˢ = ❙Ψₛₚₐₜᵢₐₗ❭ˢ❙Ψₛₚᵢₙ❭ˢ OR ❙Ψₛₚₐₜᵢₐₗ❭ᴬ❙Ψₛₚᵢₙ❭ᴬ
Antisymmetric:
❙Ψ❭ᴬ = ❙Ψₛₚₐₜᵢₐₗ❭ᴬ❙Ψₛₚᵢₙ❭ˢ OR ❙Ψₛₚₐₜᵢₐₗ❭ˢ❙Ψₛₚᵢₙ❭ᴬ
Helium Atom
──────────────────────────────────────────────────────────────────────────
Fermions, so overall must be antisymmetric
Configuration Term Energy
1s² 1s 0
❙Ψ❭ = 1/√2 (❙a❭₁ₛ❙b❭₁ₛ + ❙b❭₁ₛ❙a❭₁ₛ)❙0 0❭
1s²s 3s 1.46
❙Ψ❭ = 1/√2(❙a❭₁ₛ❙b❭₁ₛ - ❙b❭₁ₛ❙a❭₁ₛ)❙1 m❭, m=-1,0,1
1s2s 1s 1.52
❙Ψ❭ = 1/√2 (❙a❭₁ₛ❙b❭₁ₛ + ❙b❭₁ₛ❙a❭₁ₛ)❙0 0❭
1s2p 3pᵒ ~1.60
❙Ψ❭ = 1√2
1s²p 1pᵒ ~1.65

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lecture_notes/4-18 Normal file
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𝐁⋅d𝐥 = B(s) sπs = μ₀[∫𝐉⋅n̂da + ε₀ d/dt ∫𝐄⋅n̂da]
𝐉⋅n̂da = 0
For capacitor:
│𝐄│ = σ/ε₀ ⇒ B(s) 2πs = μ₀ ε₀ d/dt σ(t)/ε₀ πs²

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S𝓍 ≐ ħ͟⎛0 1⎞
2⎝1 0⎠
Diagonalize the matrix...
First, find the characteristic equation and solve for the eigenvalues.
S𝓍 ≐ ħ͟⎛0 1⎞
2⎝1 0⎠
ħ͟ ⎛-λ 1⎞
2 ⎝ 1 -λ⎠
λ² - ħ²/4 = 0
λ² = ħ²/4
λ = ±ħ/2
So the eigenvalues are those expected for the measurement of a spin-1/2 component.
The eigenvalue equations are
S𝓍❙Ψ❭ = λ❙Ψ❭
which is represented by
ħ͟⎛0 1⎞⎛a⎞ = λ⎛a⎞
2⎝1 0⎠⎝b⎠ ⎝b⎠

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After the first Stern-Gerlach magnet, the entire wave function will be in a single state:
❙Ψ₁❭ = ❙S₊❭