# Expectation of position in a 2D system

1. Mar 15, 2012

### staraptor

How does on calculate the expectation of the position operator x in a 2D infinite potential well (in the xy plane)? Do we only work with the Psi to the Hamiltonian in that particular coordinate when finding <Psi|x|Psi>?

2. Mar 15, 2012

### vela

Staff Emeritus
You calculate
$$\langle x \rangle = \iint \psi^*(x,y)\,x\,\psi(x,y)\,dx\,dy$$

3. Mar 15, 2012

### staraptor

Could you explain this please? Where does the double intergral come from?

4. Mar 15, 2012

### vela

Staff Emeritus
What does your textbook say about calculating an expectation value?

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