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University Quantum Mechanics I

University Quantum Mechanics I · The Infinite Square Well · 6.07

Measurement probabilities and what a superposition is not

An energy measurement returns Eₙ with probability |cₙ|², and the projection postulate says an immediately repeated measurement returns the same Eₙ, so we carry the state forward as ψₙ.

Course-map guide · not a complete lesson or simulation

Scope & orientation

What this subsection covers

An energy measurement returns Eₙ with probability |cₙ|², and the projection postulate says an immediately repeated measurement returns the same Eₙ, so we carry the state forward as ψₙ.

A strong response uses bar chart of |cₙ|² over n and states where the model stops being reliable.

Reasoning checklist

Evidence, assumptions and limits

01

Assumptions to state

State the system, observable, approximation, and conditions held fixed before using a model.

02

Evidence to collect

Do the resonances of a string clamped at both ends fall at fₙ = n f₁ with n - 1 interior nodes, and where does the analogy with Eₙ break?

Read the complete note

Do the resonances of a string clamped at both ends fall at fₙ = n f₁ with n - 1 interior nodes, and where does the analogy with Eₙ break? Useful evidence includes resonances for n = 1 to 6 with node positions measured, fₙ fitted against n, the fitted f₁ against v/2L, and fₙ proportional to n set beside Eₙ proportional to n² with the differing dispersion named.

03

Limits to state

This GioPhysics course map is an adaptable learning sequence, not academic credit, accreditation, or a universal university syllabus.

Read the complete note

This GioPhysics course map is an adaptable learning sequence, not academic credit, accreditation, or a universal university syllabus. It is a first dedicated quantum-mechanics course, distinct from University Physics V, which covers quantum mechanics alongside atomic, nuclear and particle physics in twenty units: this course is narrower, slower, and teaches the linear algebra it needs rather than assuming it. Hydrogen appears here as an introduction, with the full radial derivation belonging to a second course. A midterm examination is assumed around week 8. Follow your institution's published scope, notation, laboratory programme, and assessment rules. A result should be checked against units, signs, limiting cases, and the conditions under which its model was derived.

Diagram & examples

Work the claim before choosing an equation

Interactive concept map

Follow the model from claim to evidence.

01 · Physical claimMeasurement probabilities and what a superposition is not

An energy measurement returns Eₙ with probability |cₙ|², and the projection postulate says an immediately repeated measurement returns the same Eₙ, so we carry the state forward as ψₙ.

Read the complete note

An energy measurement returns Eₙ with probability |cₙ|², and the projection postulate says an immediately repeated measurement returns the same Eₙ, so we carry the state forward as ψₙ. How that transition happens is where interpretations part company and is not settled in this course. A superposition is not an unknown one of the Eₙ: the relative phases inside the cₙ are physical, and the |cₙ|² alone do not determine the state.

02 · RepresentationThe subsection's claim

Model, evidence, and boundary

03 · TestPrediction before measurement

What must be stated before selecting an equation for Measurement probabilities and what a superposition is not?

04 · Evidence & boundaryDecide, then qualify

Do the resonances of a string clamped at both ends fall at fₙ = n f₁ with n - 1 interior nodes, and where does the analogy with Eₙ break?

Read the complete note

Do the resonances of a string clamped at both ends fall at fₙ = n f₁ with n - 1 interior nodes, and where does the analogy with Eₙ break? Useful evidence includes resonances for n = 1 to 6 with node positions measured, fₙ fitted against n, the fitted f₁ against v/2L, and fₙ proportional to n set beside Eₙ proportional to n² with the differing dispersion named.

Interactive diagram for Measurement probabilities and what a superposition is not: follow the physical claim through its representation, proposed test, evidence, and model boundary.

modelModel, evidence, and boundary turns the stated idea into a representation that can make a prediction.

Example questions

Try the reasoning before revealing the structure.

Diagram check

What must be stated before selecting an equation for Measurement probabilities and what a superposition is not?

Quick check

Test the reasoning, not recall

What must be stated before selecting an equation for Measurement probabilities and what a superposition is not?

Choose an answer to test the model.