- #1

- 99

- 2

## Homework Statement

An atom in an excited state has a lifetime of 1.2 x 10 -8 sec; in a second excited state the

lifetime is 2.3 x 10 -8 sec. What is the uncertainty in energy for the photon emitted when

an electron makes a transition between these two levels?

## Homework Equations

[itex]\Delta[/itex]E[itex]\Delta[/itex]t[itex]\geq[/itex][itex]\frac{\hbar}{2}[/itex]

## The Attempt at a Solution

So I just found the uncertainty in energies for the two excited states using the uncertainty principle, getting 2.74*10^-8 eV for the 1.2*10^-8 sec state, and 1.43*10^-8 eV for the 2.3*10^-8 sec state. And figured that the uncertainty in energy would just be the difference in the energies, giving 1.31*10^-8 eV. But the book gives an answer of 4.17*10^-8 eV, which I noticed is what you get if you add the energies instead.

So is the book wrong, or is there some weird thing about the uncertainties combining such that I have to add them instead?