Textbook Question 1.3

[Megan Chan 3A]

The question asks:

In each second, a certain lamp produces 2.4×10^21 photons with a wavelength of 633 nm. How much power (in watts) is produced as radiation at this wavelength (1W = 1J⋅s^−1)?

However, the solution only provides the energy of the photons (750 J) which I was able to solve for, but I wanted the check whether my answer for the power was correct. I ended up solving for power to be 1.6x10^-12 W. Is this the answer anyone else got?

[Sunny Wu 3A]

How did you solve for power? I also calculated just now that 2.4×10^21 photons with a wavelength of 633 nm have an energy of 750 J. In the question it states that the lamp produces that many photons in one second, so the lamp produces 750 J per second. If watts is defined as J/s, then the power in watts should be 750 watts, correct? Please correct me if I'm wrong.

[Megan Chan 3A]

Oh I see, I think you may be right. I overcomplicated the problem and solved for frequency which has the unit s^-1 and multiplied that with the energy to get J.s^-1, but 750 watts should be correct from your explanation. Thank you!