## 1B7

$E=hv$

Eden Breslauer-Friedman 2A
Posts: 104
Joined: Wed Sep 30, 2020 10:11 pm

### 1B7

Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by (a) an excited sodium atom when it generates a photon; (b) 5.00 mg of sodium atoms emitting light at this wavelength; (c) 1.00 mol of sodium atoms emitting light at this wavelength?

I attached question 1B7 from the textbook above. I understand that all 3 parts of this can be solved using c=wavelength(frequency) and E=hv, but how do you go about solving for part b (5.00 mg sodium atoms)?

Thanks!

Marisa Gaitan 2D
Posts: 97
Joined: Wed Sep 30, 2020 9:47 pm
Been upvoted: 3 times

### Re: 1B7

For part b, you need to first calculate the number of sodium atoms in 5.00 mg by doing some dimensional analysis (going from mg to g to mol to atoms). Then use the energy calculated in part a and multiply that by the number of sodium atoms which gives you 44.1J

Haochen He 3L
Posts: 50
Joined: Wed Sep 30, 2020 9:37 pm

### Re: 1B7

Hi! In part a, you get the energy emitted by an excited atom. For part b, you just need to find the number of sodium atoms in 5 mg sodium (using moalr mass of sodium and avogadro's number). Then multiply the result of part a and the number of sodium atoms.

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