What is the commutator [J^hat_x J^hat_y,J^hat_z] equivalent to?

In summary, the commutator [J^hat_x J^hat_y,J^hat_z] simplifies to iħ(j^hat_z-J^hat_x)=0, but the answer given is -i=(j^hat_x,J^hat_z). To reach this answer, try adding and subtracting terms to pair with the existing terms in the original commutator.
  • #1
pinkfishegg
57
3

Homework Statement


Let J-hat be a quantum mechanial angular momentum operator. The commutator [J^hat_x J^hat_y,J^hat_z] is equivalent to which of the following

Homework Equations


[J^hat_x,J^hat_y]=iħJ^hat_z
[J^hat_y,J^hat_z]=iħJ^hat_x
[J^hat_z,J^hat_x]=iħJ^hat_y

[A,B]=[AB-BA]

The Attempt at a Solution


I tried to plug this out using commutator relations
[J^hat_x J^hat_y,J^hat_z]=J^hat_x J*hat_y J^hat_x-J^hat_xJ^hat_x J^hat_y
simplifies to
iħ(j^hat_z-J^hat_x)=0

The answer the got for the practice test is -i=(j^hat_x,J^hat_z)
im not sure how the simplified to get this answer. if i simplified mine i would just get J^hat_z=J^hat_x..
 
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  • #2
I can't follow your calculation, I do not know either what you actually meant when writing "-i=(j^hat_x,J^hat_z)" as such notation has no existing mathematical meaning, as far as I know.
So, ##[J_xJ_y,J_z] = J_xJ_yJ_z - J_zJ_xJ_y##, from this try to add and subtract some term, with which you can pair the two terms already existing in the original commutator to form commutators of the form that you have written in "Relevant equations", for example try to add and subtract ##J_xJ_zJ_y##.
 

FAQ: What is the commutator [J^hat_x J^hat_y,J^hat_z] equivalent to?

What is a Commutator PGRE question?

A Commutator PGRE question is a type of question found on the Physics GRE (PGRE) exam that tests a student's understanding of commutators, which are mathematical operators commonly used in quantum mechanics. These questions often involve calculating commutators and understanding their properties.

Why are Commutator PGRE questions important?

Commutators are an essential part of quantum mechanics and are used to describe the relationships between physical observables. Understanding commutators is crucial for solving problems in quantum mechanics and is often tested on the PGRE as a fundamental concept.

What is the best way to prepare for Commutator PGRE questions?

The best way to prepare for Commutator PGRE questions is to practice solving problems involving commutators and understanding their properties. This can be done by studying relevant textbooks and practicing with past PGRE exams. It is also helpful to review the basic rules and properties of commutators before the exam.

Are Commutator PGRE questions difficult?

Commutator PGRE questions can be challenging, as they require a solid understanding of commutators and their properties. However, with sufficient practice and preparation, they can be mastered. It is important to remember to approach these questions with a clear understanding of the fundamental concepts and to avoid overcomplicating the problems.

Can I use a calculator for Commutator PGRE questions?

No, calculators are not allowed on the PGRE. This is to test a student's ability to solve problems using only their knowledge and understanding of concepts, rather than relying on a calculator. It is important to practice solving problems without a calculator to prepare for the PGRE.

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