Problem with units when using E=hv

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Discussion Overview

The discussion revolves around the application of the formula for the energy of a photon, E=hf, and its alternative form E=hc/λ. Participants explore unit conversions and calculations related to photon energy, specifically addressing a calculation involving red light with a wavelength of 700 nm.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant states that the energy of a photon can be expressed as E=hf or E=hc/λ, linking frequency and wavelength.
  • Another participant points out that Planck's constant has units of J·s, which translates to kg·m²/s.
  • A participant suggests that the calculations presented are correct aside from potential errors in the signs of exponents.
  • One participant acknowledges a mistake in the exponent used in their calculations.

Areas of Agreement / Disagreement

Participants generally agree on the formulas for photon energy and the units involved, but there are corrections and clarifications regarding the calculations and unit conversions. The discussion does not reach a consensus on the final interpretation of the units.

Contextual Notes

There are unresolved issues regarding the accuracy of the calculations and the interpretation of units, particularly concerning the conversion of energy units and the handling of exponents.

Aspchizo
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In case I'm wrong, the formula for energy of a photon is E=hf.
Or E=hc/λ, because f=c/λ.

Basically the second formula is just in case you don't know frequency so it crams the equation for that into the equation for energy.

When I use E=hc/λ the units I get are...

kg*m2/s3

What I did was... A photon of red light, has a wavelength of like 700nM, so...

(6.626×10-34kg*m2/s2) (3x108m/s) / 7×107m

= 2.84×1019kg*m2/s3

I thought the answer would be in Joules, which is kg*m2/s2, so I must be missing something... Why the extra unit of time.
 
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Wow stupid, Planck's constant is J×s which is kg*m2/s

Well, everything else looks okay?
 
Check the signs of your exponents. Everything else looks right, if you fix your units.
 
Ah right, ^-19

Thanks
 

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