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Questions tagged [intensity]

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Doubling up on Ear Protection NRR Equation

I'm planning to go to shooting ranges soon, and am looking for ear protection. Let's say that I get an earmuff with a noise rating reduction (NRR) of $X\ \textrm{dB}$ and earplugs with $Y\ \textrm{dB}$...
Superman's user avatar
  • 111
1 vote
0 answers
46 views

Derivation of the formula for intensity of sound wave [duplicate]

I was trying to derive the formula for finding the intensity of the sound wave, after deriving it in my way i am missing a factor of 2 in the formula, Can I know what I am doing wrong ? Here is my ...
Utkarsh Kumar's user avatar
1 vote
0 answers
39 views

Intensity of light - questions about the particle standard definition and concerning the units [duplicate]

In the $5.111$ MIT class, lecture $3$, it is written on the last slide "intensity of light = photons per second". Intensity is previously defined in the lecture as the square of the ...
niobium's user avatar
  • 608
5 votes
3 answers
643 views

Does the number of photoelectrons depend on the area of the beam for a given beam power?

I don't understand something in the photoelectric effect experiment (which consists in shining light to a metallic material and then measuring the kinetic energy of the ejected electrons, as well as ...
niobium's user avatar
  • 608
1 vote
0 answers
16 views

Why is the intensity of a beam of light the squared magnitude of the phasor and not just the squared magnitude of the real part?

I'm learning about phasors and light intensity and there are two conflicting things I've been told that I can't reconcile. Firstly I've been told that a phasor $e^{-ikz+i\phi}$ is a mathematical way ...
Hadi Khan's user avatar
  • 531
2 votes
1 answer
37 views

Demonstration of constant radiance for Lambertian Surfaces

I'm approaching to radiometry and I'm struggling with one of the properties of Lambertian surfaces. We know that the radiance is the radiant flux emitted, reflected, transmitted or received by a ...
Mattia's user avatar
  • 23
10 votes
3 answers
2k views

Why is intensity additive?

In class we came across a problem that is essentially the following: Suppose a source of sound has an intensity of 70 dB. Suppose 9 additional sources produce the same sound in unison (so 10 ...
Marcus A's user avatar
  • 101
0 votes
2 answers
25 views

Converting laser irradiance into volume energy density

If I want to convert a laser's irradiance of $10^{20} \,\text{W}/\text{cm}^2$ into a volume energy density, do I just divide it by the speed of light $c$?
Phil Bouchard's user avatar
0 votes
2 answers
20 views

Question about Proportionality in Sound Equation (Pressure and Displacement Amplitude)

Why is intensity in terms of pressure amplitude inversely proportional to density and velocity: $I=\frac{\Delta p_\text{max}^2}{2\rho v}$, while in terms of displacement amplitude, it is proportional ...
Mato's user avatar
  • 19
0 votes
1 answer
55 views

Intensity of Light in a 2D Flatland?

Given the figure below, it specifies that the intensity of light at a given distance is: intensity = 1 / d^2 After working on an implementation for Radiance ...
FatalSleep's user avatar
1 vote
1 answer
31 views

If a star's luminosity doubles, does its received flux double?

If the luminosity of a star increases or decreases in some way, would the received flux increase or decrease by the same amount (linearly) or would it change by the square of the luminosity (inverse ...
Astrovis's user avatar
  • 187
2 votes
2 answers
52 views

Confusion between two equations for sound intensity

The definition of sound intensity is $I=P/S$, where $P$ is the power generated by the wave source and $S$ is the area over which the energy is transferred. Assuming conservation of mechanical energy ...
Mikołaj Nowacki's user avatar
0 votes
0 answers
14 views

Modeling an Electrolyzer System

In this study, the authors provide an equation for operating cell voltage: $V_{cell} = V_{rev} + V_{act} + V_{ohm}$, the sum of the reversible overvoltage, the activation overvoltage and the ohmic ...
Lucien Jaccon's user avatar
0 votes
0 answers
23 views

How HBT interferometery works?

I am still confused about how HBT interferometry for star angular size works after reading about it on the internet and in papers. Mathematics usually does not help before I do not catch the way the ...
saldenisov's user avatar
1 vote
0 answers
22 views

Determining the photon beam intensity to confirm the placment of an object in a iradiated chamber [closed]

A parallel bundle of monoenergetic photons is used for imaging in the configuration below. The bundle passes through a layer of water with a thickness of 1 cm, then through a zone where a cube with a ...
Ghidic Vladislav's user avatar
1 vote
0 answers
19 views

Calculating in-duct sound intensities from sound pressure measurements with mean mass flow

In the time domain and in free field condition the sound intensity can be calculated as $ \vec I(t)=p(t) \cdot \vec v(t)$ with $p(t)$ being the sound pressure and $\vec v(t)$ being the sound velocity. ...
Matthias La's user avatar
9 votes
4 answers
560 views

Getting the spectrum of light source at high intensity (for low transmittance measurement)

I am trying to measure the transmittance spectrum through a liquid sample using a visible-NIR spectroscopy (a spectrometer connected to a fiber optics and a collimating lens at the end), with tungsten-...
smk's user avatar
  • 93
2 votes
1 answer
75 views

Why we typically see no deeper into an atmosphere for an optical depth of 1?

In An Introduction to Modern Astrophysics (p.243), Carroll and Ostlie say that for a optical depth $\tau = 1$ the intensity will decline by a faction of $e^{-1}$. $I_\lambda = I_{\lambda,0}e^{-\tau}$ ...
BlurryConception's user avatar
0 votes
0 answers
24 views

Is the strongest acoustic signal always the closest?

I have a single beam echosounder that I use to measure the distance to an object underwater. It emits an acoustic pulse and listens to the reflections. Using the time of flight and the strongest ...
Apo's user avatar
  • 1
0 votes
1 answer
48 views

Derivation of intensity of a sound wave (missing calculation in the book)

The question is about a calculation in the first section of this page: https://openstax.org/books/university-physics-volume-1/pages/17-3-sound-intensity Essentially, it states: "To find the time-...
Mato's user avatar
  • 19
0 votes
2 answers
144 views

Does intensity of sound depend on temperature or humidity?

The intensity of sound $I$ can be written as $$ I = 2 \rho v (af \pi)^2$$ I googled and found that increase or decrease of temperature doesn't have any impact on sound intensity. But why is that? ...
akifsami's user avatar
0 votes
2 answers
43 views

Intensity of light and energy at a photonic level

If I understand correctly, the intensity of light is proportional to the number of photons hitting a certain area. If we then look at a single photon when described as a transverse wave, is its own ...
Richard Coppack's user avatar
0 votes
1 answer
106 views

Can we say that amplitude of light scattered by air molecules is inversely proportional to the square of wavelength of incident light?

As per Rayleigh's criteria of scattering of light by air molecules the intensity of scattered light is inversely proportional to the forth power of wavelength. AND WE ALSO SAY : Intensity of a wave ...
Shinnaaan's user avatar
  • 1,357
-2 votes
1 answer
246 views

What is $dE/dR$ and how does when $dE/dR=0$ makes electrical field intensity maximum? [closed]

Actually my question is that when $dE/dr=0$ then $dE$ also comes out to be zero then how does electric field intensity maximum when $dE/dr=0$. And also I don't understand that how does this value came ...
Physics student's user avatar
0 votes
1 answer
129 views

Intensity of central maximum for a diffraction grating

If I send a typical 5 mW, 532 nm laser pointer beam through a diffraction grating (~1,000 slits/mm), then I'd expect the beam to cover something like ~1,000 slits. The resulting intensity of the ...
greatscissors's user avatar
0 votes
1 answer
1k views

Calculating measured intensity of a Gaussian beam

Consider a light source which emits a Gaussian beam with total power $P_0$, initial width $d$, and divergence half-angle $\theta$ (in radians). The beam radius, measured from the waist of the beam, ...
mathslover's user avatar
2 votes
3 answers
269 views

Why doesn't the Intensity of laser light drop by $\frac{1}{r^{2}}$?

If we observe a laser we see its intensity wont drop by $\frac{1}{r^{2}}$ as seen for regular light sources as its very concentrated and even remain somewhat same for long distances (even though its ...
Naveen V's user avatar
  • 648
0 votes
2 answers
166 views

Is the intensity of a light wave related to frequency of the wave?

My problem is: How can I resolve these following ideas? Energy of photons in an EM wave is proportional to the frequency of the wave Intensity of an EM wave is proportional to the energy that is ...
syndromeofme's user avatar
-1 votes
6 answers
533 views

Why sound gets weaker as it travels in air? [closed]

When we talk, our vibrating chords oscilate next air molecules which oscilate the next molecules and so on. Hence sound wave travels. As we know, energy that reaches the destination is not the same ...
Giorgi's user avatar
  • 525
7 votes
2 answers
449 views

Would different sounds of the same intensity but different frequencies have the same harmful effect on the human ear?

The "safe noise exposure limits" I found on the internet only indicates the intensity of the sound in dB, but not the frequency. Does that mean that e.g. a 120dB sound with different ...
user629549's user avatar
0 votes
1 answer
165 views

Doubt in the definition of intensity

So I know that radiant intensity is defined as "power transferred per unit solid angle per unit area which is perpendicular to the direction of propagation of energy". So now I have a very ...
Ham Lemon's user avatar
  • 201
1 vote
3 answers
110 views

Why does an increase in my sound intensity lead to an increase in frequency range?

I am a biologist studying frogs, and as part of my research I use hundreds of thousands of audio recordings (.wav) from autonomous recording units. I use various software to create recognizers that ...
Anna's user avatar
  • 11
1 vote
3 answers
339 views

How to calculate the intensity of a light when using the ray model?

Suppose that there is a point light source with power $P$. We are interested in a single light ray visualised in the above picture. The ray travels a distance $r_1$ and encounters a surface. The ray ...
mathslover's user avatar
0 votes
1 answer
480 views

What is the formula for the power of a laser at distance $x$ (taking attenutation into account)?

While this is inspired by science fiction, if I have a hypothetical laser weapon that needs to meet a very high energy requirement of energies of the order $ 1 \times 10^{22} $ Joules, what formula ...
John's user avatar
  • 43
2 votes
2 answers
71 views

Are the intensities of waves equal when they are represented in real vs complex notation?

The intensities should be equal no matter how a wave is represented. So clearly I think i'm making some elementary mistake, it seems they are not same : $$ \Phi(x,t) = A_0 \cos{(kx-wt)} \\ \Phi(x,t) = ...
Kobamschitzo's user avatar
0 votes
2 answers
49 views

Defining the loudness in terms of mass and time

The unit of loudness is $$\rm\frac{W}{m^2},$$ which is equivalent to $$\rm\frac{kg}{s^3}.$$ Since kg is the SI unit for mass and s is the SI unit for time, this led me to the following question: Can ...
Jovan Radenkovic's user avatar
0 votes
0 answers
58 views

Effect of thickening polariser on intensity pattern

I've performed an experiment where microwaves were sent through a polariser of varying thickness, composed of $11$ slits (width and spacing both $6$ mm). To vary the thickness of the polariser, this ...
Trisztan's user avatar
  • 149
2 votes
0 answers
578 views

How does the intensity of light in a double slit experiment vary with the slit width?

I know this question has been asked quite a few times on the network but I still can't find a concrete answer. It's quite clear that intensity depends on the square of slit width in a single slit ...
RedMiner2005's user avatar
0 votes
1 answer
32 views

Why would there be a larger data dispersion at minimums than at maximums in a graph of intensity against path difference?

I'm doing a rather simple experiment concerning the superposition of two waves and the impact that path difference of 2 identical waves has on recorded intensity at that point. However, there is ...
Lil Kerek 101's user avatar
3 votes
3 answers
310 views

If $I$ is the intensity of the principal maximum in the single slit diffraction pattern, then what will be its intensity if the slit width is doubled?

I've found a few results on the internet for this question, all with different explanations or different answers. Some say it'll become 4I and some that it'll not change. I see that there are a few ...
Solitary Solus's user avatar
4 votes
1 answer
281 views

Decibels, acoustic intensity and sound perception

I know the formula: $I[dB] = log_{10}\left(\frac{I}{I_0}\right)$ with $I$ being the acoustic intensity in $[W/m^2]$ and $I_0 = 10^{-12} [W/m^2]$ being the human threshold of hearing. Also, I am told ...
c.leblanc's user avatar
  • 197
1 vote
1 answer
278 views

Deriving the Interference Intensity of Michelson interferometer

I am trying to equate the equation i found wikipedia: To the one given in my course notes which is: Assuming a 50/50 beam split i have 1/2 where i should not have one:
Jack Jack's user avatar
  • 187
2 votes
2 answers
61 views

Question about unit for intensity

The picture is from one physics textbook about treating sun as a blackbody and compare the electromagnetic radiation spectrum. Note the unit used for Intensity in the picture shown, it's Watts / (...
user526427's user avatar
0 votes
0 answers
21 views

Why a wave whose intensity is modulated sinusoidally have different frequency compared to original wave even though intensity depends on amplitude?

While experimenting to find the velocity of light, instead of finding the velocity of light, we used the light wave whose intensity was varied sinusoidally and found the velocity of light using the ...
Adithya's user avatar
1 vote
1 answer
118 views

Derivation of the exoplanetary flux observed at Earth (solid angle problem)

I'm having issues understanding how Sara Seager, in her book "Exoplanet Atmospheres", determines the solid angle subjected to a detector on Earth. By the figure: The solid angle was defined ...
Fitzroy's user avatar
  • 15
5 votes
2 answers
1k views

Sound waves adding up [duplicate]

If there is a swarm of bees, why is it louder than a single bee? This question may sound stupid but ... if they are all buzzing at the same frequency with the same loudness and the phases of the sound ...
Hyp's user avatar
  • 159
0 votes
1 answer
18 views

If the range of a laser depends on its crossection perimeter does it mean that a wider beam would reach much longer distances?

If the range of a laser depends on its crossection perimeter does it mean that a wider beam would reach much longer distances? Let pressume that we can construct a 1m wide laser beam and as we know ...
Krešimir Bradvica's user avatar
0 votes
0 answers
69 views

Acceleration due to incident radiation on plate

I have tried the following question and getting a wrong answer. Monochromatic light of intensity I falls over a blackened plate of area A, at an angle $\theta$ as shown in the figure. If 70% of light ...
PSR_123's user avatar
  • 134
1 vote
1 answer
1k views

Convert $\rm Lux$ to $\rm W/m^2$

I use four LED matrix (UV, green, red, blue) to irradiate a solar panel with an area of S at a distance. The matrix is located at a distance l from the solar panel. I want to plot the volt-ampere ...
Сергей Корягин's user avatar
3 votes
1 answer
950 views

What is the displacement amplitude of a 140 db sound wave?

I am teaching a unit on sound in my upper elementary science class, and my students are curious about how far air molecules are actually being displaced in a sound wave. I told them that if the air ...
Sarai Leia's user avatar