# Homework Help: Derivation of "continuity equation"

1. Feb 13, 2007

### Ami

Hello,

I need the derivation of "continuity equation" by the current density equation,in Quantum Mechanics.

I really need this derivation quickly,please

Thanks

Last edited: Feb 13, 2007
2. Feb 13, 2007

### Tom Mattson

Staff Emeritus
You can do it yourself.

1. Take the Schrodinger equation for $\Psi(\vec{x},t)$ and multiply it by $\Psi^*(\vec{x},t)$.
2. Take the Schrodinger equation for $\Psi^*(\vec{x},t)$ and multiply it by $\Psi(\vec{x},t)$.
3. Subtract the two equations.

From there you have to appropriately define the probability density and the probability current density, then finish off the manipulations to get the continuity equation. Try that, and if you get stuck post what you have done and we will get you un-stuck.

3. Feb 16, 2007