# 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 $Y\ \textrm{dB}$...
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1 vote
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### 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 ...
1 vote
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### 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 ...
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### 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 ...
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1 vote
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### 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 ...
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### 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 ...
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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 ...
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### 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 $c$?
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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 ...
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### 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 ...
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### 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 ...
1 vote
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. ...
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### 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-...
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### 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 $e^{-1}$. $I_\lambda = I_{\lambda,0}e^{-\tau}$ ...
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### 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 ...
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### 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-...
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### 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? ...
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 ...
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 ...
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### 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 ...
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 ...
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### 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, ...
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### 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 ...
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### 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 ...
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 ...
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### 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 ...
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 ...
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### 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 ...
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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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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 ...
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 ...
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### 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:
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### 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 / (...
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### 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 ...
1 vote
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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