Practice Textbook Problems

[Ethan Goode 2H]

A lamp rated at 32W(1 W=1 J⋅s−1) emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s? How many moles of photons are emitted in that time interval?

Which equation would you use to do this problem? I am struggling starting.

[Chem_Mod]

Hi, you would use the E = hv equation. Don't forget that the E in that equation is Energy per photon (in other words J/photon). Sometimes if you're stuck, you can try looking for ways to cancel units to get your final result, which in this case is photons. I hope this helps you start this question.

[anikamenon2H]

For this problem, the first thing you need to do is find the energy per photon, using E = hc/λ. Once you find the energy per photon, you should calculate the total energy the light is providing in the 2.0s (which would be 64 W or 64 J/s). Then you can divide the total energy (64W) by the energy per photon that you calculated to find out how many photons are being emitted by the lamp. Then use Avogadro's number to find how many moles of photons are emitted in that same interval.

Hope this helps!