## 1B 9 7th edition

$E=hv$

Abby De La Merced 3F
Posts: 30
Joined: Fri Sep 28, 2018 12:24 am
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### 1B 9 7th edition

Quick question - when finding the number of photons of violet light that can be generated in 2.0 s, why do you divide 64 J by 4.7 x 10^-19 instead of multiplying the two values?

Xiangkun Shi 3E
Posts: 31
Joined: Fri Sep 28, 2018 12:25 am

### Re: 1B 9 7th edition

You can think of it this way. The energy of each photon is 4.7 x 10^-19J. If we multiply this energy by number of photons, we will get the total energy. Since now we want to get the number of photons, we do it backwards by dividing the total energy with energy per photon.

Andonios Karas 4H
Posts: 30
Joined: Fri Sep 28, 2018 12:27 am

### Re: 1B 9 7th edition

64 Joules is the total energy emitted by the lamp in 2 seconds.
4.7 x 10^-19 Joules is the energy per photon emitted.
We want to know the number of photons emitted in those 2 seconds.
Etotal = Ephoton * #photons
Therefore, #photons = Etotal/Ephoton