Energy-Time Uncertainty

• Recall for photons E = hf

• uncertainty in energy => uncertainty in f

• ?f= ?E/h ??= 2??f ??.?t ? 1

• introduce “h-bar” h = h/2?

• ?E . ?t ? h

• need infinite time to make an accurate measurement of energy

• eg. Ground state of atom has well defined energy

• excited state does not

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