# What is Intensity: Definition and 958 Discussions

Sound intensity, also known as acoustic intensity, is defined as the power carried by sound waves per unit area in a direction perpendicular to that area. The SI unit of intensity, which includes sound intensity, is the watt per square meter (W/m2). One application is the noise measurement of sound intensity in the air at a listener's location as a sound energy quantity.Sound intensity is not the same physical quantity as sound pressure. Human hearing is sensitive to sound pressure which is related to sound intensity. In consumer audio electronics, the level differences are called "intensity" differences, but sound intensity is a specifically defined quantity and cannot be sensed by a simple microphone.
Sound intensity level is a logarithmic expression of sound intensity relative to a reference intensity.

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1. ### How to show light from laser pointer is plane polarised?

The answer key is the light is directed through one polarising filter then filter is rotated and the light changes intensity. I don't understand how that proves that the light is plane polarised. I think if the light is unpolarised, the intensity will also change when it passes through...
2. ### Electric field amplitude question regarding intensity calculations

My question is specifically with calculating the intensity. The book solution is I=P/(4*pi*r^2) but would this not give me a weaker electrical amplitude in the final calculation after plugging it in to I=(1/2)*√(ε0/μ0)*(E02) ?
3. ### I Light intensity required to shine a light through an opaque object

Pretty much, I was picturing a 1x1x1 meters cube of a dark colored, mostly uniform material (limited porosity, no crevices) with a small chamber in its interior - exactly where the center of mass should be. In it, a body emitting light is activated with the goal to find the intensity necessary...
4. ### Effect of a polarizer/analyzer on partially polarized light

This is problem 62 in Cutnell & Johnson's Physics (9th edition): Suppose that the light falling on the polarizer in the figure is partially polarized (average intensity \bar S_P) and partially upolarized (average intensity \bar S_U). The total incident intensity is \bar S_P+ \bar S_U and the...

Consider the infrared led TSAL7600 which has the following properties: $$\Phi = 35 mW$$ $$I_e = 25 mW/sr$$ The half angle is ## 30^\circ ## and: $$I_r(\theta) = cos^{4.818}(\theta)$$ is a good approximation for the relative radiant intensity. However, finding the actual radiant...
6. ### Graphing Power vs Polarizer Angle using Intensity

The data collected from the experiment is, The first column is the polarizer angle measured in degrees. The second column is recorded intensity measured in lux. The third column is the transmitted intensity measured in lux. This is equal to the recorded lux - ambient lux The fourth column is...
7. ### I Gamma radiation decay intensity (IAEA nuclide chart)

I was looking at the gamma radiation data from IAEA's website: (https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html) and was confused by the absolute intensity listed in the page. I Googled it and it seems to be the probability of emission but why it doesn't add up to 100%? For example...
8. ### Intensity of a wave at half amplitude and twice frequency compared to a reference wave

TL;DR Summary: How do i find the intensity of this wave? I know I is proportional to amplitude / frequency squared, but I don't know what equation this comes from. And I don't know how to answer this.
9. ### B If I double sound on my PC, how would the sound intensity increase?

If I have on my PC let's say sound on 50% and I increase it on 100%, how would the sound intensity change? Would it be twice bigger? But I think that function of sound intensity level dependent on sound percets is a linear function, isn't it? How to explain it? Why is it the linear function?
10. ### Distance between the first and third maximum intensity detected

My answer is 0.5 m (same as wavelength) but answer key is 1 m. I thought the maximum intensity occurs at antinode and distance between adjacent antinodes is half of wavelength so the distance between first and third antinode is one wavelength. Where is my mistake? Thanks
11. ### A Realizing EIT with Pulsed Laser: Intensity, Duration & Frequency

I have realized EIT with continuous laser. What are the requirements for the intensity, duration and repetition frequency if EIT is realized with pulsed laser? you can attach any reference:biggrin:thanks a lot!

13. ### Procedure to express radiation intensity of an LED in watts/cm^2

I am calculating Responsivity of a pn junction photodiode (a.k.a the target) by irradiating radiation from LED sources. For this purpose, i have two LEDs, one UV and another green LED. Note that LEDs are placed close to the target. UV LED : Manufacturer has given total radiant power to be...
14. ### Work and energy of electromagnetic wave with intensity I

a) ##\rho = \frac{I}{c} = \frac{F}{A}## for a perfect absorber ##F = ma## where ##a = \frac{c}{t}## ##\frac{I}{c} = \frac{mc}{tA}## ##I = \frac{I^2 tA}{mc^2} = \frac{P}{A}## ##P = \frac{I^2 tA^2}{mc^2} = \frac{W}{t}## ##W = \frac{I^2 t^2A^2}{mc^2}## I am unsure what A is. I think it should be...
15. ### Two slit interference: new intensity after doubling width

Here is the solution, I understand how they got E, but I don’t see how they could get E’ from cosine addition formulas? I don’t need to know how to do it with complex numbers.
16. ### Total intensity of 3 slits

Here’s an image of the equations better layed out here’s the solution, I don’t understand how they are squaring it to get the time average
17. ### Spectral Intensity Formula by Using Frequency

I found there is kind of solution in Pointon's book: An Introduction to Statistical Physics for Students. But I don't know how to find intensity by using frequency.
18. ### Intensity Distribution of Superposition of 2 Waves

We assume incident waves to be: y(1)=y(o)sin(wt) y(2)=3y(o)sin(wt+Φ) As Intensity~(Amplitude)^2 We get y(2)=3y(1) This gives us I(2)=9I(1) We assume I(1)=I(o) & I(2)=9I(o) Resultant Wave Intensity I=I(1)+I(2) +2√(I(1)*I(2))*cosΦ ----> I(o) + 9I(o) + 6I(o)cosΦ (We can take cos of this...
19. ### Intensity of a laser beam at a certain distance

I haven't been able to pinpoint a definition of "angular divergence" of a laser so by pure intuition I assumed it would be something like ##\theta=\frac{2R}{D}## and with that I have that the radius of the lase beam is ##R=\frac{D\theta}{2}=90\cdot 5 \cdot 10^{-6} m=450\ \mu m## so...
20. ### Fresnel diffraction from square: on axis intensity

I'd appreciate if someone could check whether my work is correct. The ##x##-##y## symmetry of the aperture separates the Fresnel integral:\begin{align*} a_p \propto \int_{-a/2}^{a/2} \mathrm{exp}\left(\frac{ikx^2}{2R} \right) dx \int_{-a/2}^{a/2} \mathrm{exp}\left(\frac{iky^2}{2R} \right) dy...
21. ### Question on sound intensity and dB

Would we have to use the 3-dB exchange rate? How would we solve this question?

23. ### Magnitude and average value of energy intensity of light beam

I tried using the equations above, but I wasn't really able to come up with an intuitive explanation. From my understanding, the electric field vector only varies in the x-y plane while the magnetic field vector only varies in the z-y plane. Also, both vary sinusoidally and both reach extrema...
24. ### I Calculating Intensity in Single Slit Diffraction Experiments

In a single slit diffraction experiment, when we want to calculate the intensity of light on a screen located very far away from the slit, usually Huygens' principle is adopted as a model to perform the calculations. It is assumed that the width of the slit consists of an infinite number of...
25. ### Intensity and electric field amplitude

Hello. I am having some trouble to understand the resolution of this question. We could easily try to calculate the electric field relative resultant at the screen. The problem i am having is about the amplitude of the electric field: Generally, we have that the intensity part dependent of the...
26. ### Proving that the incident intensity is not the same as the sum of others

I was supposed to find the relation among the coefficients $T$ and $R$ which represent the amplitude of the reflected electric field and the transmitted electric field respectively, that is, $$E_{R} = E_{i} R, E_{T} = E_{i} T$$ as well as the coefficients $t$ and $r$, that represent the...
27. ### Find the intensity as function of y (interference between two propagating waves)

Let a spherical wave propagate from the origin, $y = ADcos(wt-2\pi r/ \lambda)/r$. Also, let a plane wave propagate parallel to the x axis, $y = Acos(wt-2\pi r/ \lambda)$. At x = D there is a flat screen perpendicular to the x axis. Find the interference at the point y on the screen as function...

40. ### Find the electric field intensity from an infinite line charge

what I've done so far? -i've determined the vector between the point (4, 0, 0) and the point P. (4, 6, 8) - (4, 0, 0) (0, 6, 8) -The norm of this vector is the radial distance of the line to point P (the value of “ρ” in the formula) √(0^2 + 6^2 + 8^2) = 10 -> ρ = 10 -and its unit vector is...
41. ### A traveling wave on an infinite string, find the intensity

The answer is about 40 Watts, but i am really not getting it: <Pot> = 0.5((pλ)(ωA)²)v p density linar λ wavelength ω angular frequency A amplitude v phase speed Why is this wrong? (I already tried too by <Pot> = Z*(ωA)²/2) Z is impedance
42. ### Intensity of Stars and the Inverse Square Law Problem

1. speed of light = 3*10^8 ms^-1 length of an Earth year=365 days*24 hours*60minutes*60seconds=3.15*1 0^7 seconds distance=speed*time 1 light year= 3*10^8 *3.15*10^7=9.46*10^15m 4.2 light years = 4.2*9.46*10^15m=3.9732*10^16m ~ 3.97*10^16m (to 3sf) 2. Intensity=power/area Power=1.4MW=1,400,000...
43. ### To find the resultant intensity

So I thought of calculating the path differences between all the 3 points by taking them in pairs of 2. S1 and S2 S2 and S3 S3 and S1 I got the path differences as λ/3 , λ and 2λ/3 I can now find their phase differences using the equation Cosx=2π/λ* (path difference) Then I can apply the...
44. ### I Are Intensity and Magnitude independent of the radius of a star?

For a star.. Apparent Magnitude = -2.5log10 I K And I = I0/d^2 So in terms of I0... Apparent Magnitude = -2.5log10 (I0/d^2) And the Stefan-Boltzmann law says: Energy Flux = Sigma(T^4) In my reading it says that Intensity is the energy emitted per unit of area per unit of time. It says the same...
45. ### Intensity of a Harmonic Wave

To begin with, I am trying to understand how does ##E^2 (x,t)## transform to ##A_y^2 + A_z^2##. And, noting that the already established equation of ##E^2 = E_y^2 + E_z^2##, I would assume that ##E^2 (x,t)## somehow ends up to being ##A_y^2 + A_z^2##. However, noting that ##E^2 = (A_y...
46. ### Sound intensity - How to deal with decibels?

I was looking up the maximal amount of noise allowed by current laws, that one can produce. I found that in my region one can produce sounds of up to 45 dB in the period from 22 pm to 7 am. But, it seems evident that the decibels fall off as we distance ourselves from the source. So shouldn't...
47. ### Brewster's angle and the intensity of reflected light

Hi, Would it be correct to say that at Brewster's angle, all the incident light which has its electric field parallel to the plane of incidence gets refracted, and the rest of light whose electric field is perpendicular to the plane of incidence gets reflected? For example, if the light whose...
48. ### Intensity and Interference Patterns (double slit)

I'm still on part a. I think that i may have the wrong equation for intensity. I'm not sure I'm using the right numbers for the "first minimum". I started with getting the wavelength λ=(ax)/D since the first minimum occurs at m = 0.5 I multiplied the distance to the first minimum by 2 to get...
49. ### Clarification on field intensity (electromagnetism)

Is the intensity of a general electromagnetic wave always the norm of its Poyinting vector? Or are there other notions of intensity?
50. ### Polarization and intensity of a Gaussian beam

The equation above (from Wikipedia), assumed that the Gaussain beam has polarization in x-direction, as I know that the polarization means that the oscillation direction of the electric field and so the intenisty... so how we get circular intensity in every direction which means in x and y...