Quantum Physics Approximation Methods

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Questions and Answers

Why is 0 equal to ±1 in the context of Stark effect?

  • To conserve angular momentum (correct)
  • To cause four-fold degeneracy
  • To maintain energy balance
  • To prevent Zeeman effect

Which perturbation theory method deals with time-dependent interactions?

  • Time-dependent perturbation theory (correct)
  • WKB method
  • Variational method
  • Time-independent perturbation theory

What causes the Stark effect according to the given text?

  • Interaction between electric dipole and electric charge (correct)
  • Variational method
  • WKB method
  • Zeeman effect

What is the significance of the condition m = m0?

<p>Ensures conservation of angular momentum (C)</p> Signup and view all the answers

In the n=2 case, how many nonzero elements result from the condition 0 = ± 1?

<p>Two (B)</p> Signup and view all the answers

What determines the first-order correction in energy of the first state of the hydrogen atom?

<p>Angular momentum (D)</p> Signup and view all the answers

What property restricts the nonzero matrix elements to h2, 1, 0 | z | 2, 0, 0i in the n=2 case?

<p>Angular momentum conservation (D)</p> Signup and view all the answers

Which effect arises from the exchange of photons with spin 1?

<p>Stark effect (B)</p> Signup and view all the answers

Which method is used to calculate the fine structure corrections in the hydrogen atom?

<p>WKB method (B)</p> Signup and view all the answers

What contributes to the four-fold degeneracy in the n=2 case?

<p>Interaction with magnetic field (D)</p> Signup and view all the answers

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Study Notes

Approximation Methods in Physics

  • Time-independent perturbation theory
  • Time-dependent perturbation theory
  • Variational method
  • WKB method

Fine Structure and Hydrogen Atom

  • Hydrogen atom has fine structure due to interactions
  • Energy levels of hydrogen atom are affected by external electric field (Stark effect)

Stark Effect

  • Electric analogue of Zeeman effect
  • Hydrogen atom develops an electric dipole moment in an external electric field
  • Energy levels of hydrogen atom split due to Stark effect
  • Additional term HStark in the Hamiltonian of H-atom

Hydrogen Atom under Electric Field

  • Constant and uniform electric field ∊ in z-direction
  • HStark = -|e|∊z

Energy Correction due to Stark Effect

  • Expectation value of HStark in the state |n, , m is required
  • Lz and z commute, so [Lz, z] = 0
  • m = m0 for non-zero matrix elements
  • ≠0, rather 0 = ± 1

Selection Rule for Stark Effect

  • 0 = ± 1 due to electric dipole interacting with electric field by exchanging photons with spin 1
  • Angular momentum of electron decreases or increases by 1 only

Matrix Elements for Stark Effect

  • Non-zero matrix elements of the form: hn, , m | z | n0, ( ± 1), m i

Example: Ground State of H-Atom

  • First-order correction in energy: E1,0,0 = 0, since 0 =

n=2 Case

  • Four-fold degenerate: |2, 0, 0i , |2, 1, 1i , |2, 1, 0i , and |2, 1, −1i
  • Non-zero elements: h2, 1, 0 | z | 2, 0, 0i and h2, 0, 0 | z | 2, 1, 0i
  • First-order correction in energy: E2,,m = ±|e|a0 ε

Historical Overview

  • Johannes Stark (1874-1957) - Physics Nobel Prize (1919)
  • Antonino Lo Surdo (Italy, 1913) - observed the same effect, known as Stark-Lo Surdo effect

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