# Questions tagged [intensity]

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### Formula to measure distance of light from a flashlight [closed]

My question is: Can a flashlight of $14 \ \mathrm{cm}$ width illuminate a marble (a ball made with glass) at $15.1\ \mathrm{km}$ distance? at night with no moonlight? Can you tell me the formula by ...
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### Electron emission and photoelectric effect affected by intensity

It is said that when visible light is directed onto a metal surface, it doesn't emit electrons from the surface because intensity doesn't affect it. However, then it is said (relating to the equation) ...
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### Will I be able to see a light coming from a laser in the edge of the universe?

It is said that light's intensity decreases with increase in distance. Suppose if there is a laser in complete vacuum, emitting a collimated light beam from one end of the universe for about 93 ...
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### Does emission of electron depend on colour instead of brightness of light?

According to photoelectric effect we consider light to be particles to justify the threshold wavelength in light. It says that the energy of electron emitted depends on wavelength of light that falls ...
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### Electric field intensity $E$

Electric field intensity (E) is defined as the electrostatic force experienced by a unit positive charge , mathematically E = F/q,it seems like the mathematical equation E = F/q contradicts the ...
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### Why is acoustic intensity inversely proportional to density of the medium?

The definition of sound (acoustic) intensity is given by $$I = {p^2 \over {\rho c}} \;\;\;\; \text{or} \;\;\;\; I = {p^2 \over {2\rho c}}$$ I've seen both definitions in different textbooks and am ...
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### Doubt regarding intensity received at a point

I came across a problem which is as follows: Screen S is illuminated by two point sources A and B. Another source C sends a parallel beam of light towards point P on the screen (see figure). Line AP ...
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### Relationship between intensity and sound level

So I know that for every tenfold increase in intensity, the sound level increases by 10 dB. So if the intensity is increased by a factor of 100000, the sound level increases by 50 dB. I also know that ...
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### wondering light polarization, enjoying three dimensional cinema

I am very fascinated by physics, but I'm not much into it beacuse I studied it as an amateur many years ago. I'm trying to understand things about optics and polarization of light, and in particular ...
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### Solar panel voltage reducing by adding cellophane

For a physics report, I am aiming to answer the question How does the power output of a solar cell vary with the thickness of cling wrap laid over it? I got a negative relationship between voltage and ...
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### Coherent and non-coherent sources

As we know, if we superpose two coherent sources of intensities $I_1$ and $I_2$, the resultant intensity is not merely equal to $I_1 + I_2$ but sometimes can be much less and much more than that value....
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### Blue laser scattering in the atmosphere: At what distance the laser source is no more seen as a pointlike source due to Rayleigh scattering?

Blue laser scattering in the atmosphere: At what distance the laser source is no more seen as a pointlike source due to Rayleigh scattering? Does this distance depend of the intensity of the laser ...
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### Spectral Radiation Intensity and Energy Density

I'm trying to prove the following relation $$I_{v} = \frac{c}{n} u_{v}$$ where $I_{v}$ is the (spectral) radiation intensity and $u_{v}$ is the respective energy density, $n$ is the refractive index ...
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### Double-slit diffraction: Reduction of intensities

In a double-slit experiment, why do the intensities of the interference maxima decrease with the increasing diffraction angle?
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### Cauchy-Schwarz inequality in terms of intensity measurements

Hi I was reading Introductory Quantum Optics by Gerry and Knight, particularly the part about higher degrees of coherence (Section 5.4), and in there they write: Now according to Cauchy’s inequality ...
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### Intensity of light transmitted by a polarizer when the incident light is unpolarized

my question is similar to this older one, but I have not enough privileges to answer it or comment on it. I do realize that the question has received detailed answers by Selene Routley, and I sort of ...
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### If 30dB at 200 meters away, how much at origin? [closed]

I want to organize an event in a public area, and I'm not sure how loud we can get. If the limit is 30 dB as measured at 200m away from the origin of the sound, what is the limit from its origin, in ...
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### Expressions for emitted and incident flux of a star confusion

The physical flux is the total energy flowing across the unit area from all directions: We can write flux as a function of intensity as follows: F = \int_0^{2\pi}\!\!\! \int_0^{\pi} I \cos(\theta) \...
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### Linking brightness of object to intensity of light reflected from it

If an object seems brighter than it actually is, is it correct to assume that intensity of light reflected by it is high due to multiple internal reflections, it does brightness have nothing to do ...
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### Division of intensity of sound

Consider a single sound source $(S)$ producing sound wave of intensity $I$ . It is connected to a detector $(D)$ through two paths with a path difference. My doubt is that will the intensity of ...
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### Why is contribution to intensity of light equal for both magnetic and electric field?

In chapter on waves, my sir taught us that intensity of wave is directly proportional to the square of amplitude of wave. So when we were asked what is contribution of electric field and magnetic ...
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### Changes to an EM-wave that is propagating in an inflating space

I am trying to get an easier picture of what happens to an em-wave considering space expansion. My question is: If a star in a non-inflating space emits light recorded at a certain distance of the ...
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### Gain saturation and power saturation in lasers

I have difficulty understanding the concept between gain saturation and power saturation in lasers. How are they different?
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### Is the intensity of light ONLY dependent on the number of photons, and nothing else?

Recently, my teacher just told us that intensity is not linearly dependent on temperature and that it's ONLY dependent on photons. But then, what about Boltzmann's law? Isn't intensity dependent on ...
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### Why is Stopping Potential Independent of Frequency of Photoelectron?

All the books and internet articles I have read so far claimed that the stopping potential and the maximum kinetic energy attained by a photoelectron is independent of the intensity with which the ...
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### Relation between activity, intensity, count rate and so on considering ionizing radiation

I'm currently doing a project on waste products of nuclear power. To narrow it down, I chose to focus on gamma rays in particular. However, I generally find it hard to see the relation between ...
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### Complex intensity in electric field (transfer matrix)

Currently I'm coding a transfer matrix approach in C#. Hence, I come up with certain electric fields $E$. At each position I have a propagating field to the right $E_{\text{right}}$ and one to the ...
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### Intensity in Single-Slit Diffraction

Source: https://openstax.org/books/university-physics-volume-3/pages/4-2-intensity-in-single-slit-diffraction Why is there a $2\pi$ in the numerator of the phase difference equation? I understand ...
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### Please help me formulate (and solve) a differential equation for a practical DIY problem concerning air sterilization (for covid)

Here I present the DIY air sterilisation project which this is about. I want to calculate the overall sterilization rate of the device under some simplifying assumptions. (UVC is the hard ultra violet ...
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### Photoelectric Effect Graph: Interpretation of Intensity vs

After performing dimensional analysis of the current versus voltage graph when studying the photoelectric effect, this graph should measure units of siemens. It shows, however, high intensity and low ...
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### Sound intensity [closed]

A policeman measuring motor vehicle noise is exactly 7.5m from the line of traffic on a straight road . The Sound Intensity Level ( SIL) reading shown on his meter is 86 dB. An isolated house faces ...
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### Why does "$|E|^2 \propto$ the number of photons" follow from "$\epsilon_{photon} = hf$"?

For my introduction to quantum physics course we are using the book "University Physics volume 3", availabe here, in the linked chapter in the first paragraph of the "Using the wave ...
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### Find function which minize variance of intensity on target plane

I am trying to find continuous function $\sigma(x)$ for uniform intensity. I set two parallel horizontal lines with length $W$ and with distance each other $H$. The upper line is a target plane ...
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### Why is electric current during charging battery equal to vb1-vb2/r1+r2 and any resistance in circuit

Why when we connect two batteries in series but in opposite directions current equals vb1-vb2/r1+r2. I can't understand why we subtract the current of the smaller battery from the greater battery. I ...
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### Gravitational intensity of Earth

My task is to compute the gravitational intensity $E(\vec{r})$ inside Earth. I can use the spherical symmetry of the task to use $\vec r = (r, 0, 0)$ (here $\vec r$ is inside Earth), I integrate over ...
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### Light: Intensity vs Brightness

Is the intensity or brightness of light the same idea? In other words, when we are observing Malus's law, are we looking at the "brightness" of light? If they are not the same quantity, how ...
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### Variation of Intensity when a source moves

When a sound source moves, frequency perceived by the observer is changed due to the doppler shift. Does this apply to intensity too? If yes then how. Thanks!
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### Radiative transfer equation for a three-level system

I am trying to derive the radiative transfer equation for a three-level system, which is supposed to be given by: \$\frac{dI(\omega,x)}{dx}+N [\alpha\rho_{11}-\beta( \rho_{22}+\rho_{33})]I(\omega,x)=\...
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### Will non-radially radiating sound plane wave propagate forever without losing intensity?(assuming no dissipative forces)

I have encountered on a textbook that established the relationship that intensity is proportional to the square of displacement amplitude and the square of angular frequency. However, the equation ...
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### Why do I obtain the wrong total power when integrating this Fraunhofer diffraction irradiance pattern for a circular aperture?

I am looking for some help understanding something. I am working through my optics textbook (Hecht, 4th Edition), and am following the example of the far-field Fraunhofer diffraction pattern caused by ...