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Postive or Negative Frequency

Posted: Mon Oct 14, 2019 4:11 pm
by Emily Vainberg 1D
Question on the Atomic Spectra Module asks: Calculate the frequency of a photon emitted by a hydrogen atom when an electron makes a transition from the fourth to the second principal quantum level.

I did the calculations and got
A. -6.17 x 10^14 Hz

However, it said my answer was wrong. Are frequencies suppose to be positive or was my math incorrect?
Rest of the answer choices:

B. 1.62 x 10^-15 Hz

C. 6.17 x 10^14 Hz

D. 2.71 x 10^-52 Hz

Re: Postive or Negative Frequency

Posted: Mon Oct 14, 2019 4:26 pm
by Abby Soriano 1J
Your math was correct but the answer is C because, although energy can be expressed as a negative value for energy lost, when calculating things such as frequency or wavelength, you always use positive values since there is no such thing as a negative frequency, for example.

Re: Postive or Negative Frequency

Posted: Mon Oct 14, 2019 4:32 pm
by sarahforman_Dis2I
Emily Vainberg 1L wrote:Question on the Atomic Spectra Module asks: Calculate the frequency of a photon emitted by a hydrogen atom when an electron makes a transition from the fourth to the second principal quantum level.

I did the calculations and got
A. -6.17 x 10^14 Hz

However, it said my answer was wrong. Are frequencies suppose to be positive or was my math incorrect?
Rest of the answer choices:

B. 1.62 x 10^-15 Hz

C. 6.17 x 10^14 Hz

D. 2.71 x 10^-52 Hz


Like the other user said above, your math is totally correct and the negative sign is really just a conceptual sign to illustrate where the energy is going. In reality, you cannot have "negative energy." Since the electron is moving from a higher to a lower energy level, the electron is losing energy (therefore the negative sign), but the emitted photon does not have a negative value.