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5

Yes excited states have a non-zero lifetime. Electronically excited states of atoms have lifetimes of a few nanoseconds, though the lifetime of other excited states can be as long as 10 million years. The decay probability can be calculated using Fermi's golden rule. The lifetime is then an average lifetime derived from the decay probability. The lifetime ...

1

The characteristic time of interaction - energy of interaction relation between two systems is usually written as $\delta E\cdot\delta t\sim\hbar/2$ (do NOT mix with the uncertainty principle). So the characteristic time would be about $\delta t\sim\hbar/(2\delta E)$, where for $\delta E$ we can take the difference of energies between two states.

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Your answer appears to be correct, bar the lack of any electric charge in your formula. If the applied force is solely due to a cosinusoidally varying electric field at a given position (you can ignore the magnetic component of the Lorentz force only if the charge moves non-relativistically), then so is the acceleration. Integrating this with respect to ...

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Photo-emission from a metal surface is a multistep process. When the photon hits the metal surface it excites a photoelectron with a very high quantum yield, but that photoelectron is travelling in the same direction as the photon i.e. down into the metal. For an electron to be emitted from the surface the initial photoelectron has either to ricochet back ...

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