# Talk:Intensity (physics)

Active discussions
WikiProject Physics (Rated Start-class, Mid-importance)

## What affects intensity?

What affects intensity?--User:68.12.168.125 00:28, 14 November 2005 (UTC)

Intensity of what? Intensity is a very general concept, and what "affects" it depends on what the intensity is of.
(By the way, you should "sign" your talk page posts by putting four tildes ~~~~ at the end. The wiki converts this into a link to your user page. I added your ID to your post.)--Srleffler 12:54, 14 November 2005 (UTC)

## Intensity of a EM-wave

The formula ${\displaystyle I={\frac {cn\epsilon _{0}}{2}}|E|^{2}}$  seems to be wrong. I found the formula ${\displaystyle I={\frac {c\epsilon _{0}}{2n}}|E|^{2}}$  in the textbook Introduction to Electrodynamics from David J. Griffiths. I don't have the time to find the error in the deduction, though. — Preceding unsigned comment added by 141.84.219.200 (talk) 15:45, 13 August 2013 (UTC)

Check how that author defines "E" carefully. I've seen authors define "E" to be something other than the actual electric field amplitude, sometimes introducing factors of n.--Srleffler (talk) 06:29, 14 August 2013 (UTC)

My advice is not to use symbols like n, if you can't explain them (or when there is no source). Even in this Talk nobody explains what n is. Very disappointing!— Preceding unsigned comment added by Koitus~nlwiki (talkcontribs) 14:11, 15 June 2020 (UTC)

The symbol n represents the refractive index, and it is defined in the article the first time it appears. --Srleffler (talk) 00:56, 16 June 2020 (UTC)

## Strength

Is "strength" being used in a particular sense here? Signal strength? Wikipedia policy discourages linking directly to a disambiguation page, unless it's the amorphousness of the term that's under discussion. I've been re-pointing links away from the disambiguation page strength, but I can't figure out what precisely was meant in this article, and thus which article I should re-link the word to. Would someone with expertise help, please? Sanguinity 19:45, 24 August 2006 (UTC)

What was really needed was strength. This comes up a lot with disambiguation pages for common words. People often link to them when what they really want is a dictionary definition. Such links should always be disambiguated to a Wiktionary link.--Srleffler 03:55, 25 August 2006 (UTC)
Ah! Thanks much. I'll add the wikt entry to my arsenal. Sanguinity 18:21, 25 August 2006 (UTC)

I have cleaned up the lead section to make the new reader understand the particular sense of intensity that is being used here. Everyday analogies have been expanded, and truncated statements and repetition removed. Maths section re-formatted to make more readable. Dougsim (talk) 09:06, 27 December 2012 (UTC)

Cleaning up the lead was a good idea. I made some further changes. I removed the example of incorrect usage ("intensity of pressure"), since the explanation of it had grown too long. We should not spend that much text in the introduction on talking about an incorrect usage. I removed some use of the first and second person, per WP:TONE.
I fixed the grammar in the math section. It's not correct to start sentences with "Where". The style I have used, which is common in physics writing, treats equations as phrases embedded in the sentence surrounding them, so the text introducing the equation, the equation itself, and the explanation of the variables can all be a single, grammatically correct, sentence.
The inverse square law does not cause things to decrease proportionally to the square of distance. Rather, it describes that decrease, in the cases where it occurs. It's not a fundamental physical law.--Srleffler (talk) 18:42, 27 December 2012 (UTC)

## Merriam Webster and OED Online definitions of intensity (physics)

Neither the cited Merriam Webster entry for 'intensity', nor the relevant yet uncited OED Online entry, supports the current opening sentence in the Wikipedia article, which states currently:

'In physics, intensity is the power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy.[1]'

The Merriam Webster entry for 'intensity' (2) states:

2: the magnitude of a quantity (such as force or energy) per unit (as of area, charge, mass, or time)

The OED entry for 'intensity' 2.a. states:

2.a. The degree or amount of some quality, condition, etc.; force, strength, energy; degree of some characteristic quality, as brightness, etc.; esp. in Physics, as a measurable quantity.

1794 J. Hutton Diss. Philos. Light 291 The light of greatest intensity, which is supposed to be white.

1794 R. Kirwan Elements Mineral. (ed. 2) I. 26 Denoting the degrees of intensity of some particular qualities by figures.

1831 D. Brewster Treat. Optics xxii. 200 To compare the polarising intensitiesof different crystals.

1881 J. C. Maxwell Treat. Electr. & Magnetism (ed. 2) I. 168 The force on a small charged body is proportional to its own charge, and the force per unit of charge is called the Intensity of the force.

"intensity, n." OED Online, Oxford University Press, March 2019, www.oed.com/view/Entry/97479. Accessed 3 April 2019.

http://www.oed.com/view/Entry/97479 193.116.99.226 (talk) 19:38, 3 April 2019 (UTC)

Thanks for pointing that out. Looking back through the history, I see that the reference was added in 2015 by an editor with a habit of referencing the first sentence of articles to a dictionary entry. That editor is now blocked for a variety of problematic editing behaviors. I'm going to just remove the reference.--Srleffler (talk) 03:50, 5 April 2019 (UTC)