In this question:

A He-Ne laser emits red light of the wave length $\lambda = 632.8\ \mathrm{nm}$ with a beam diameter of $2.0\ \mathrm{mm}$ and a power output of $1.0\ \mathrm{mW}$ [...] (d) How many photons are there in the $1\ \mathrm{m}$ long laser beam?

In part (d) I am not sure if the $1\ \mathrm{m}$ here is referring to the wavelength or the length. Can anyone explain it to me?


closed as off-topic by ACuriousMind, John Rennie, Kyle Kanos, user36790, John Duffield Apr 6 '16 at 16:38

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – ACuriousMind, John Rennie, Community, John Duffield
If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Hi and welcome to the Physics SE! Please note that this is not a homework help site. Please see this Meta post on asking homework questions and this Meta post for "check my work" problems. $\endgroup$ – John Rennie Apr 6 '16 at 9:43
  • $\begingroup$ What @JohnRennie said is true, but I would note there is a conceptual question here. I've edited to make it clear. That doesn't necessarily make the question on topic, since our homework policy does have two requirements, ask a conceptual question and show an appropriate amount of effort. $\endgroup$ – David Z Apr 6 '16 at 9:51
  • $\begingroup$ @Mew please don't post answers in the comment section $\endgroup$ – David Z Apr 6 '16 at 10:17
  • $\begingroup$ @DavidZ, nevertheless I've converted my comment to an answer. $\endgroup$ – Kenshin Apr 6 '16 at 10:19
  • $\begingroup$ @Mew you can let him know yourself (as you did). It's easy to forget sometimes, even for high-rep users. $\endgroup$ – David Z Apr 6 '16 at 10:21

Total length. The wavelength is already provided as 632.8nm.


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