Questions tagged [intensity]

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Radiation Intensity from a point charge in a circular motion around a static charge

A particle with charge $-q$ moves with a uniform angular velocity $\omega$ in a circular orbit of radius $a$ in the $xy$-plane, around a fixed charge $+q$, which is at the centre of the orbit at $(0,0,...
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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 ...
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Intensity of circularly polarized EM wave after linear polarizer

When a circularly electromagnetic wave is normally incident on a linear polarizer, what are the properties of the output wave? From what I understand, it will be a plane EM wave, but what about the ...
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3 votes
1 answer
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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 ...
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Is spectral radiancy same of a blackbody radiation for area element $dA$ imagined in different orientation?

Spectral emissive power $e$ is defined as the power emitted through per unit area per unit frequency. And spectral radiancy $f$ (frequency, $T$) is the energy falling perpendicular to a unit area per ...
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How was the black body intensity vs wavelength (or frequency) radiation curve historically produced?

I have read that Wilhelm Wien gave his formula to match the radiation curve of a black body as shown in the picture; which works well in high frequency region. Another formula by Rayleigh-Jeans is ...
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2 answers
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Does, and if so, why does the frequency of light and wavelength of light affect the photoelectric current?

It makes sense that intensity of light affects the photoelectric current, but what about the frequency and wavelength, given that intensity remains constant? The formula for intensity would be I = nhf/...
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Why the intensity of a wave is $ \Psi \Psi^*$?

In here at the bottom, it says the intensity of a wave is the wave phasor times it's conjucate $$ I(x) = \Psi \Psi^* = |\Psi |^2$$ But when I compute the intensity of an electromagnetic wave in c.g.s, ...
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How does the spot size of light change the photocurrent?

I want to understand the photo electric effect. If I shine light at a surface then a photon can knock an electron off the surface if its energy $h\nu$ is larger than some minimum material specific ...
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I have seen people define frequency or amplitude in two ways, which one is correct?

I have a doubt on frequency and amplitude,I have seen people define these things in 2 ways,for instance, people define frequency in mainly 2 ways,if we draw a pressure-position graph of a sound wave,...
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Why solar flux concentrators can achive only $\rm 1500°C$ of temperature if Sun temperature is $\rm 5500°C$?

Why solar flux concentrators can achive only $\rm 1500°C$ of temperature if sun temperature is $\rm 5500°C$ ? If it is possible to concentrate a flux from a parabolic mirror of area $\rm 400\ m^2$ to ...
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Sound, additive principle or not? How to prove?

If we have $N$ sound sources with $L_1, L_2,...$ with intensities $I_1, I_2,...$. How to prove that $I_{total}= I_1 + I_2 + ... $ but $L_{total}$ is NOT $L_1 + L_2 + ... $
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Is there a way to calculate the intensity of light absorbed that passed through a solid?

So I have lab I need to do for school and I need a formula that calculates the intensity of light transmitted through a solid (in my case sheets of paper). I had a probe that measured the intensity of ...
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Compute UVC Irradiance On A Surface

I would like to be able to get a ballpark approximation of the Irradiance on a surface at a distance away from a UV source. The datasheet gives the following: Radiant Power Lambertian Emitter Graph ...
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3 answers
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Law of amount of interference between different Sun rays that fall on a distinct point on Earth?

The double slit experiment shows that rays comming from different locations can cancel each other when touching a point on a screen if they are out of fase because of their wave properties. Is the ...
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1 answer
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How does intensity depend on slit-width regarding Fraunhofer diffraction?

For a single slit, considered to be infinitely long, with size $b$ the intensity at any angle is given by: \begin{equation} I(\theta)=I(0) \bigg( \frac{\sin \beta}{\beta} \bigg)^2 \end{equation} ...
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Mathematical Derivation of Expression for the Total Power Received By Earth from Sun, via Integration [closed]

I recently tried to derive an expression for the total power received by the earth from the sun, using integration. However, I am stuck at an integration step. Would appreciate if anyone could help ...
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Is the intensity of light dependent on number of photons per unit area?

I was learning about the photoelectric effect of light and there it says more the intensity of light, the more number of electrons will be ejected from the metal surface given that the frequency of ...
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How is energy in terms of Intensity and Amplitude comparable to Energy in terms of Frequency?

Let's take LASER light. It has a high energy ,in terms of Amplitude, let's take a red light, of same frequency ,we are giving each of these to two atoms , now atom no $1$ is subjected to LASER light ,...
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Unequal arm length Michelson Interferometer Light Intensity

Imagine a Michelson interferometer with unequal arm length. A laser beam with an electric field of the form $$E(t,z) = 2E\cos(ωt+kz)$$ is incident on a 50/50 beam-splitter. The first arm is of length <...
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4 votes
1 answer
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Inverse Square vs Exponential

I feel a little foolish asking this, but I keep reading sources which say that for an inverse square law relationship, e.g. light intensity vs distance from source, the intensity decays exponentially. ...
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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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Poynting vector and intensity of a signal

Given a plane monochromatic electromagnetic wave propagating in $x$ direction, with associated electric and magnetic fields of the form: $\overrightarrow{E}(x,t)=\overrightarrow{E_0}\cos(kx-\omega t), ...
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2 answers
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Photoelectric effect with high frequency and low intensity of light [closed]

What happens to the number of photons striking the free electrons on metal surface with high frequency and low intensity of light? High and low intensity of light of photons to electron on metal ...
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Photon irradiance and solid angles

A blackbody is in equilibrium with a radiation field at $\nu$ when $$ I(\nu)=\frac{8 \pi \nu^{2} }{ c^{2}}\left(\frac{1}{e^{h \nu / k T}-1}\right) $$ where $T$ is the temperature of the blackbody and $...
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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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1 vote
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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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Why do we add intensity instead of pressure for sound waves? [duplicate]

If two sound sources cause sound levels of 50dB and 53dB independently at a certain point, to measure the sound level at that point we have to first convert each sound level (dB) to its intensity ($ W/...
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Relation between Displacement Amplitude and Intensity of Sound Waves

How do we derive a relation between the displacement amplitude and the intensity of a sound wave? I saw a formula on the internet regarding the same i.e But I can't find a way that would help me in ...
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Wine color vs. quantity

Looking down at red wine in a glass, if the quantity of wine is doubled, the color darkens. Is there an equation that describes how the color changes as the quantity of wine is increased? Is it ...
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2 votes
1 answer
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How to calculate charge density [closed]

I am trying to solve this exercise: Using this formula calculate electric intensity $$ \vec{E} = \frac{\vec{c}\times \vec{r}}{r^4} $$ $\vec{c}$ is constant vector, $r$ is magnitude of the position ...
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Electric field/intensity for complex envelope

When calculating the propagation of a pulse I can either use an envelope-based or a carrier-based approach. For the carrier-based approach I can define my (focused) pulse with the central frequency $\...
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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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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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1 vote
2 answers
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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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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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2 answers
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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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1 vote
1 answer
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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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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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4 votes
5 answers
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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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1 answer
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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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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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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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