Questions tagged [intensity]

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1answer
202 views

What determines how much power goes into each diffraction order?

Imagine a grating with infinite number of slits, and the spacing D between slits is larger than the wavelength so that there are high order diffractions. In each of the diffraction directions the ...
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0answers
28 views

Below what threshold of intensity can a ray of light be considered absorbed?

Say I have a beam of light of intensity I. I'm modeling its traversal through a medium which absorbs light. As it travels, I reduce its strength by a certain specified factor. Below what intensity ...
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0answers
24 views

Energy density and specific intensity

How to derive this energy density from Maxwell's equations and where does the expression for specific intensity come from? I compute a isotropic scatter and I don't know where to get these two ...
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3answers
7k views

How strong are Wi-Fi signals?

My family members dislike the idea of having many devices communicating wirelessly in our house, arguing that the signals have negative effects on our physical health. I would like to tell them the ...
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1answer
207 views

Intensity of superimposed waves at the michelson inferometer

The Problem is about the Michelson Inferometer described by the picture below Let the Beam Splitter be one, who reflects half of the intensity and transmits the other half of it. Furthermore assume ...
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1answer
114 views

Quantum description of intensity measurement

The traditional way to formulate the measurement of the intensity in an optical field is by using the number operator $$ \hat{n} = a^{\dagger} a . $$ In effect one can say that the intensity, which is ...
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1answer
195 views

How to use Malus's law to get real output energy from a polarizer

As we know, the Malus's law is: $I=I_0\cos^2\theta$ Presently, I have a polarizer system (one half wave plate in front of a polarizer) in the lab, and have a powermeter. So, I can get two key ...
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1answer
203 views

What is the relation between Reflectance and Intensity?

I am just reviewing Fresnel's equations where Reflectance $R$ is equal to $$R=|r|^2$$ where $r$ is the complex reflection coefficient. Is there an equation that relates $R$ to intensity or is there ...
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0answers
8 views

Calculating intensity from Debye formula for Iron

Following is the question I am trying to answer: and this is what I have done so far: Any idea how I can progress from here? I think plotting a graph of intensity against |K| or 2*theta is the way ...
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2answers
80 views

What does 'per unit frequency' refer to?

We were discussing Kirchoff's theorem on blackbody radiation in class today and the equation was: $$e_{f}= J(f,T)$$ $e_f$ was defined as power per unit area per unit frequency. What does per unit ...
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2answers
36 views

The meaning of the area in the intensity equation $I = P/A$

I am a bit confused on what the area A means in the equation for intensity. I know that the area here uses the surface area of the sphere equation and the book I use says that A is the area of the ...
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0answers
56 views

Electric Field Intensity

The electric field intensity everywhere is $E=E_0-j$ (y-direction) in vacuum (say $E_0=5$). if you have an infinite-perfect conductor starting at the $x \geq 4$ plane and $x < 4$ is vacuum. What ...
4
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3answers
281 views

How to explain the relationship between wave's amplitude and intensity?

I have the following statement which I don't know how to explain: Suppose I have 2 identical monochromatic waves (same intensity and phase) shooting into the same receiver. If each wave's intensity ...
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1answer
41 views

Power and intensity of a sound wave

So in the case of a point source of a sound wave in a sphere, I'm wondering why the Intensity decreases with $r^2$ because if i setup the formula the Power always increases with $r^2$. So these two ...
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0answers
18 views

Is this the correct interpretation of specific intensity?

I've always been taught to define specific intensity as the following quantity: if I have a detector here next to me with an area element $dA$ and I detect a power element $dP$ from a source of solid ...
2
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1answer
44 views

Brightness of colors

I have 1W lights, red and green. If I turn the red light full power I get 1W red light, if I turn green light full power, I get 1W green. If I want to mix the lights and get yellow light, which has ...
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0answers
53 views

Are / Why are the H II regions positively charged?

One of the questions in our recent astrophysics course homework was to find the general opacity $\kappa$ of H II regions. We know that the H II regions are almost entirely ionized hydrogen and I ...
0
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1answer
26 views

How can I quantitatively compare the average sound intensity of two different audio clips? [closed]

Let's say I have two different sound clips of two different people snoring. The intensity of the audio in both clips will be fluctuating throughout and peak when the person is inhaling. Is there an ...
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0answers
25 views

Gain Coefficient of lasers and intensity paradox?

It can easily be shown that the intensity of a laser is $$I = I_0e^{z\gamma} \,, \tag{1}$$ where $\gamma$ is the gain coefficient. It can also be shown that $$\gamma = \frac{\gamma_0}{1+I/I_{\text{...
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4answers
4k views

Does light intensity oscillate really fast since it is a wave?

If you shine light on a wall, what will be seen is a "patch" with constant intensity. However, if light is viewed as a wave, then it is oscillations of the electromagnetic field changing from 0 to the ...
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0answers
57 views

Photoelectric effect - the reason for exponential graphs and a misconception about the concept of intensity

We have this basic PASCO Photoelectric Effect equipment in our lab and there are two things I would like to ask about the experiment. We keep either the area apertures or wavelength filters fixed and ...
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3answers
48 views

Intensity of the resultant of two complex waves [closed]

Suppose I have two waves: $Y_1= a_1e^{i(wt-kx1)}$ and $Y_2= a_2e^{i(wt-kx2)}$ I know by superposition $Y= Y_1+Y_2$ and intensity $(I) = |Y|² $ But how can I solve it. It seems hard for me to find the ...
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1answer
29 views

Luminostiy, Flux, Intensity definitions and meaning

I am taking astrophysics course and we are constantly talking about Luminosity,Brightness,Intensity,Flux etc. I thought that I understand the idea properly but I see now that I dont. Intensity is the ...
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1answer
91 views

Reflection coefficient derivation

from fresnel equations we have $$r_{parallel}=\frac{n_1\cos\theta_i-n_2\cos\theta_r}{n_1\cos\theta_i+n_2\cos\theta_r}$$ $$r_{perpendicular}=\frac{n_2\cos\theta_i-n_1\cos\theta_r}{n_1\cos\theta_i+n_2\...
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1answer
10k views

Relation between intensity of light and amplitude of electric field?

A question in my textbook involve finding the electric field amplitude at a point in space given the intensity of light. It uses the following equation to solve it: - $I=\frac{1}{2}\epsilon_{0}|E_{...
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3answers
213 views

How is energy conserved during simultaneous refraction and reflection of light?

My question is regarding the partial reflection and refraction of light when incident on a refracting surface. Here, the energy of Incident Ray is E=hv of Reflected Ray is E=hv and that of Refracted ...
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1answer
140 views

Photoelectric Current [duplicate]

Recently learnt that Intensity= nhv ; where n is the number of photos per unit area My textbook specifies that the photoelectric current only depends upon the number of photons striking per unit time ...
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1answer
88 views

Calculating light intensity with Fresnel's Equations [closed]

When light gets reflected or transmitted by another medium it's intensity splits for both the parallel and perpendicular component. Using Fresnel's equations calculating the reflected intensity which ...
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1answer
117 views

why does the intensity of light does not vary with time in youngs double slit experiment

[ we can see that resultant electric field at a point p is given $E=E0\sin(kx-\omega t+\epsilon)$[equation highlighed with yellow color] as the resultant field varies with time, why not ...
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4answers
25k views

How much lux does the Sun emit?

I want to know how much lux the sun emits on a bright day - I don't mean when one stares directly at the sun, but rather when one walks casually outside when the sun is shinning brightly. Now the ...
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1answer
332 views

Converting illumination to irradiance

I need get intensity of an LED light source, but I cannot convert lux to $W/M^2$ How does one convert illumination to irradiance? And what is the irradiance formula?
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2answers
351 views

A Question About Brewster's Law

In most textbooks I read, they state that when the angle of reflection + angle of refraction = 90, there is maximum polarization. What I don't understand is what maximum polarization means. Does it ...
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1answer
37 views

A Physics Problem Involving Refraction [closed]

I'm not sure how to solve this problem. I've considered using Malus' law, but then I don't know what theta is, preventing me from solving this problem.
4
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3answers
200 views

Energy conservation in the combination of two coherent beams

I was asked a question today by a student that I couldn't find a satisfactory answer to. Imagine we have two identical laser beams with average electric field strength $E$. Upon combining these beams ...
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3answers
423 views

What does K means in The Inverse Square Law? [closed]

Today in class i have learned the inverse square law and i was given the equation $I=K/d^2$ for some constant K. What does K really means?? I know that it is a constant but how can you get K or where?
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6answers
4k views

What does it mean to make a sound twice as loud? [duplicate]

Giancoli Textbook question: To make a given sound twice as loud, how should a musician change the intensity of the sound? The given answer is: "Increase the intensity by a factor of 10." I don't ...
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1answer
105 views

Wave optics, intensity distribution

Do Gaussian beams have a gaussian intensity distribution? If so, why? Does the intensity distribution depend on the profile of the light beam?
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4answers
101 views

What does the intensity profile of a set of parallel rays look like after travelling through a convex lens?

I have had a discussion at my university about the following question. Imagine a 'perfect' convex lens and a set of parallel rays, falling onto that lens. The set of incoming rays has a flat intensity ...
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1answer
29 views

Noise level x amount of meters away from an outdoor singer: sphere or semi-sphere?

When computing the noise level x amount of meters away from a singer who is singing outdoors, should one rely on the standard formula $I=\frac{P}{4πr^2}$ (and then convert 'I' into decibels) or ...
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2answers
1k views

What does “intensity of light” mean?

In this lecture from MIT, the professor defines the intensity of a wave as the square of the amplitude of the wave. But, at the same time, the professor defines the intensity of light as the number of ...
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0answers
46 views

Derivation of scattering coefficient as a function of number density of scatterers

I'm trying to derive the usual formula for intensity of light passing through scattering medium: $$I=I_0\exp(-\alpha x),$$ where $\alpha$ is the scattering coefficient (assuming it's constant), and $...
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2answers
2k views

How do polarized sunglasses reduce glare?

How do polarized sunglasses reduce intensity? When unpolarized sunlight enters our eyes through linearly polarized sunglasses the intensity is reduced. How can I understand it from the expression of ...
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1answer
8k views

What is the formula for the intensity of light, and how are amplitude, frequency and number of photons considered?

One formula for light intensity is$$ I = \frac{nfh}{At} \,,$$where: $n$ is the number of photons; $h$ is Planck's constant; $f$ is the frequency; $A$ is the incident area; $t$ is time. Another ...
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0answers
30 views

“Intensity” as a unified term

I am seriously having trouble with the word “intensity”. Does it have different meanings when it is placed next to another word (light intensity for example) or does it always mean the same (power/...
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4answers
404 views

Relationship between intensity and electron emission from a metal?

Here's the question: A xenon arc lamp is covered with an interference filter that only transmits light of 400- nm wavelength. When the transmitted light strikes a metal surface, a stream of electrons ...
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0answers
42 views

Quadratic relationship between amount of light and intensity

In a spectroscopy experiment, we were able to control the amount of light shining onto a sample by adjusting two small slits. By investigating the relationship between slit width and the intensity of ...
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1answer
40 views

Photon energy and power

My question has to do with the solar spectrum. I understand sunlight is composed of light of different wavelegnths, and these wavelegnths have different energies associated with them. I also ...
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0answers
22 views

How much information can be yanked out of an XRD Graph?

I have an XRD Graph(plotted data peaks between 2theta and intensity).I already Know the d-value corresponding to each peak.The material has an orthorhombic symmetry.What more information can I ...
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0answers
140 views

How is radiance conserved? - Power/intensity misconception

Before getting to the main question I'd like to clear some pretty basic concepts regarding energy/power/intensity as my physics is pretty rusty. According to wiki In radiometry, radiant flux or ...
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1answer
56 views

Acoustic amplitude transmission through multi layer medium

I have an acoustic wave with amplitude $A$ in ice. It passes a water-filled crevasse, and I want to calculate the impact of this passage on the magnitude of the amplitude (I do not care for the phase)...