PLEASE HELP Question regarding uncertainty principle

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SUMMARY

The discussion centers on the application of the uncertainty principle in quantum mechanics, specifically the relation ΔEΔt > h/4π. The user correctly identifies Δt as 10^-10 s and seeks to calculate the uncertainty in energy (ΔE) and frequency (Δv) associated with a photon emitted from an excited atomic state. The confusion arises when the user calculates Δv and obtains an unreasonably high value of 7.96 x 10^8 m/s. The community clarifies that the frequency should be expressed in Hz (s-1), not m/s, and emphasizes that the calculated Δv should be compared to the typical frequency range of visible light, which is 1014 to 1015 Hz.

PREREQUISITES
  • Understanding of the uncertainty principle in quantum mechanics
  • Familiarity with the concepts of energy (ΔE) and time (Δt)
  • Basic knowledge of photon emission and atomic excited states
  • Ability to perform unit conversions between frequency (Hz) and velocity (m/s)
NEXT STEPS
  • Study the derivation and implications of the uncertainty principle in quantum mechanics
  • Learn how to calculate energy and frequency using the Planck constant (h)
  • Explore the relationship between energy, frequency, and wavelength in electromagnetic radiation
  • Investigate the properties of excited states in atoms and their role in photon emission
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Students and professionals in physics, particularly those studying quantum mechanics, as well as educators seeking to clarify the uncertainty principle and its applications in atomic physics.

xregina12
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Analogous to the uncertainty relation ΔpΔx > h/4π, there is an uncertainty relation for the time and energy, ΔEΔt > h/4π that stems from the methods
usually used to measure the energy. The uncertainty in the time, Δt, can be interpreted as a lifetime. The excited state of an atom responsible for the emission of a photon has an average lifetime of 10^-10 s. What is the corresponding uncertainty in the frequency associated with the emitted photon?

What I understood based on the uncertainty principle:
ΔEΔt > h/4π and that Δt=10^-10 s here in this problem.
I can use this to calculate ΔE.
However, my next step is something I am not sure about. I set ΔE=hΔv and solved for v but then got 7.96x10^8 ms-1 which is so big and doesn't make sense to me.

Can anyone explain what I did wrong, why, and give me some guidance on what I should do to get the uncertainty in frequency?
 
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xregina12 said:
What I understood based on the uncertainty principle:
ΔEΔt > h/4π and that Δt=10^-10 s here in this problem.
I can use this to calculate ΔE.
However, my next step is something I am not sure about. I set ΔE=hΔv and solved for v but then got 7.96x10^8 ms-1 which is so big and doesn't make sense to me.

Can anyone explain what I did wrong, why, and give me some guidance on what I should do to get the uncertainty in frequency?
Do you mean for the units to be s-1 or ms-1?

Either way, consider that visible light has a frequency in the range of 1014-1015 Hz (or s-1). Compared to that, does your Δv value appear to be large or small?
 

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