What is Intensity: Definition and 963 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. W

    Intensity of elliptically polarized light

    The time averaged norm of the Poynting vector of this electromagnetic field (elliptically polarized light): \begin{split} \bar{E}(t,\bar{x})=&(\bar{E}_{0x}+\bar{E}_{0y}e^{i \delta})e^{\bar{k}\cdot\bar{x}-\omega t}\\ \bar{B}(t,\bar{x})=&\frac{1}{\omega}(\bar{k}\times\bar{E}(t,\bar{x}))...
  2. S

    Diffraction grating, number of slits, and intensity

    Homework Statement Got a question in a school examination, but here's the part I want to ask. How does the number of slits per unit length, affect the intensity of the diffraction pattern? What I do know is that the finer the slit separation, the wider the angle opens up. But intensity is...
  3. C

    A proton is placed in an electric field of intensity 700 N/C

    A proton is placed in an electric field of intensity 700 N/C. What is the magnitude and direction of the acceleration of this proton due to this field? in a google I found that 1 proton= 1.6022 x 10 ^ -19 and 1.6726 x 10 ^ -27 kg so I first get the force : F= q*E f= (1.6022 x 10 ^ -19...
  4. S

    Should luminous intensity be a fundamental unit?

    It seems to me that luminous intensity should really be put in terms of energy, not a special unit (which itself is based on some arbitrary specification of energy.) The other 5 units and Avogadro's number should be the only fundamental units.
  5. A

    B field intensity of 2 parallel wires

    Homework Statement Two long parallel wires are a center-to-center distance of 4.60 cm apart and carry equal anti-parallel currents of 4.40 A. Find the magnetic field intensity at the point P which is equidistant from the wires. (R = 4.00 cm). Homework Equations magnetic field for a...
  6. T

    Blackbody radiation intensity find maximum

    Homework Statement By direct calculation, derive and expression for the wavelength λ(max) at which blackbody radiation intensity is a maximum [b]2. Homework Equations Planck's law for the intensity distribution of blackbody radiation as a function of wavelength λ and the blackbody...
  7. C

    What is the wave intensity formula for sound?

    Our physics teacher gave us a formula to calculate intensity, she didn't really specify what intensity, it should be related to sound. I = intensty A = amplitude P = Density F = frequency V = velocity pi = 3.14 she said I = 2*(pi)^2*A^2*P*F^2*V I can't find anything like this in books or...
  8. M

    Elliptical partially polarized beam and its intensity

    Homework Statement A partially elliptically polarized beam of light, propagating int he z direction, passes through a perfect linear polarization analyzer. When the transmission axis of the analyzer is along the x direction, the transmitted intensity is maximum and has the value of 1.5 I[0]...
  9. S

    Can Laser Intensity Stabilization Be Improved for Precise Measurements?

    I'm working with a setup involving a collimated laser (Thorlabs model CPS180), two polarizers, a beam splitter, and 2 photo-diodes. While measuring the intensity of the laser via LabView, without changing any of the components, I find the intensity varies by 0.2mV for the first hour of...
  10. M

    Measuring intensity of superposed waves using complex amplitudes

    Hi, Suppose we have the x and y components of the electric field being described as (E_{x}e^{i(kz-\omega t)}, E_{y}e^{i(kz-\omega t +\phi)}), what is the intensity? I think the correct answer is E_{x}^{2} +E_{y}^{2} + 2E_{x}E_{y}\cos\phi. However, I am not sure how to deal with this using the...
  11. M

    How does IR (infrared) intensity measured

    Can a lux meter measure infrared intensity like it does for the visible light? I read from somewhere that it cannot. If you have an IR illuminator on in the dark and hold up your 'regular' lux meter to it, it will likely register 0 - an unhelpful and misleading result. I'm just wondering if...
  12. G

    Intensity and Power of Sound

    Homework Statement The sound intensity level of a certain sound source is measured by two listeners located at different positions along a line from the source. The listeners are located on the same side of the source and are separated by 34.8 m. The listener that is closest to the source...
  13. S

    Why do I get a higher radiation intensity with slight shielding than with none?

    Homework Statement I did a radiation lab a few weeks back. The task was basically to map out radiation intensity as a function of shielding thickness. A Cs137 gamma ray source was used, and lead was used as the shielding material. Data was taken meticulously and over long periods of time so as...
  14. E

    What is the intensity of sound 2?

    Homework Statement Sound 1 has an intensity of 39.0 W/m^2. Sound 2 has an intensity level that is 2.5 dB greater than the intensity level of sound 1. What is the intensity of sound 2? Homework Equations I=energy/area*time β=(10dB) logI/Io Io=10^-12 W/m^2 The Attempt at a Solution...
  15. S

    Intensity and the Double Slit Experiment.

    In viewing a derivation of the formula describing the intensity of the interfering waves, I noticed how the electric field components were combined - one from slit a, the other from slit b. The intensity is then proportional to the square of this value. But this would mean that two in phase...
  16. B

    Solving for Intensity of Light Through a Polarizer

    Homework Statement Vertically polarized light with an intensity of 0.65 W/m2 passes through a polarizer whose transmission axis is at an angle of 30.0° with the vertical. What is the intensity of the transmitted light? I0 = 0.65 W/m2 theta = 30.0 degreesHomework Equations...
  17. L

    Diffraction grating, angular with of the intensity peaks to the first maximum

    Homework Statement A diffraction grating is ruled with 500 lines/mm and is 1 mm in width. Calculate the angular width of the intensity peaks to the first minimum in the Fraunhofer diffraction pattern of this grating, when illuminated with light of λ = 600 nm. Homework Equations n-...
  18. A

    Reflection and Transmission Intensity of randomly polarised light

    Homework Statement A randomly polarized beam of light hits a water surface at Brewster angle. What is the intensity of the transmitted and reflected beams? The refractive index of water is n = 1.33 Homework Equations The Attempt at a Solution Since the light is randomly polarised...
  19. C

    Intensity of Light With a Given Power of Through a Polarizer

    1. Homework Statement A 200 mW horizontally polarized laser beam passes through a polarizing filter whose axis is 25 degrees from vertical. What is the power of the laser beam as it emerges from the filter? P=mW 2. Homework Equations I0cos2(theta) I≈E0cos(theta) I=E0cos2(theta)...
  20. T

    How Do Distance and Power Affect Sound Intensity Levels?

    Second problem of the day...:blushing: Homework Statement (part 1 of 2) A spherical source radiates sound uniformly in all directions. At a distance of 52 m, the sound intensity level is 46 dB. At what distance from the source is the intensity level 13 dB? Answer in units of m...
  21. M

    Photoelectric Effect and intensity of light

    OK, so i have a question about the nature of light, in the context of the photoelectric effect. So when photons are incident on a metal, given that they have a high enough frequency they can cause electrons to be emitted from the metal. Now i know that intensity of light is to do with the...
  22. S

    Intensity in Electromagnetism versus probability density in Quantum Mechanics

    In the book Introduction to Quantum Optics: From the Semi-classical Approach to Quantized Light by Grynberg, Aspect and Fabre I came across the following statement on page 385: "By the end of the nineteenth century, classical electromagnetism,..., provided a wave description of almost all...
  23. D

    Intensity Distribution of 4 Slit diffraction grating using convolution

    Hi all, I am trying figure out this diffraction problem. I have to find the intensity distribution of a four slit fraunhofer diffraction grating using the convolution theorem. I can do the math and all...but I do not know how to start it! The only information I am given is the slits have...
  24. P

    Calculating Light Intensity from Sunlight for Solar Food Dehydrator

    Hi there, im doing school project regarding Solar Food Dehydrator. Can tell me what is the formula to calculate the light intensity from the sunlight?
  25. Drakkith

    How to Calculate Intensity in Airy Disk from a Point Source?

    I'm trying to figure out the intensity of light in different sections of a 2d airy disk from a point source, but I'm not sure how to calculate it. Does anyone have any good sources?
  26. T

    Deriving formula for final intensity of light through three polarizers.

    Homework Statement Show that the exit intensity as a function of Io (intensity out of light source) and θ12 (angle of second polarizer compared to the first polarizer) is I = (Io/8) sin(2(θ12)))^2 Homework Equations Malus' Law I = Io (cosθ)^2 The Attempt at a Solution I1 =...
  27. D

    Intensity of Electromagnetic Waves

    Homework Statement A plane monochromatic electromagnetic wave with wavelength λ = 2.2 cm, propagates through a vacuum. Its magnetic field is described by \vec{B} = (Bx\vec{i} + By\vec{j})cos(kz+ωt) where Bx = 1.8E-6 T and By = 3.8E-6 T, and i-hat and j-hat are the unit vectors in the +x and...
  28. majormaaz

    Sound Intensity and Bird Watching

    Homework Statement A bird watcher is hoping to add a particular song bird to the list of species she has seen. If a person, only 2.35 m from the bird, hears the sound with an intensity of 1.9 10-6 W/m2, how far could the bird watcher be from the bird and still hear it? Assume no reflections or...
  29. M

    Light intensity of UV component from a xenon lamp

    I have a 100watt xenon lamp , the UV component comprises of 5-6% of the total spectrum emitted by the xenon lamp . How do I calculate at what power is the UV light emitted ? Is the whole spectrum being emitted at 100 W or is the power distributed through the spectrum? How is this...
  30. L

    Double Slits experiment central fringe intensity

    Homework Statement In a double slits experiment, the intensity at the central fringe is I. What will be the intensity at the central fringe when each slit is widened 2 times? Homework Equations The Attempt at a Solution My suggestion is that the intensity will be 2I...
  31. C

    Using Phasors to Graph Intensity vs Angle (4 slits)

    3.a) Use phasors to sketch the intensity vs. angle for a 4-slit interference pattern (identical width and separation d=5 microns, wavelength =0.5 microns.) b) On the same angular scale, draw the intensity pattern if the top two slits are covered. c) The intensity pattern if the bottom 2...
  32. M

    Ultrasound - intensity reflection coefficiant calculations

    Homework Statement The following table gives some specific acoustic impedances Tissue or Medium Specific acoustic impedance Air 0.00044 x 10^6 Fat 1.38 x 10^6 Water 1.5 x 10^6 Brain 1.58 x 10^6 Blood 1.59...
  33. C

    How do i rank magnetic field intensity given amperes?

    Is the magnetic field intensity at point P stronger at 2 amps or 4 amps at point P (just outside each electromagnet), if they both have equal amounts of turns of wire. No relative equations. I know that magnetic field intensity is stronger as the number of loops are increased but I...
  34. S

    Light Intensity transmitted through the polarized and analyzer

    Homework Statement Here is the question:Unpolarized light of intesity Io is incident on a polarizer-analyzer pair. If the angle between the polarizer and analyzer is 21°, what light intensity is transmitted through the polarizer and analyzer respectively? Your answers will be in terms of...
  35. C

    Varying Intensity of Gravitational Field and Equivalence

    Hi all, I was just looking for some assistance in reconciling the equivalence principle and the varying intensity of the gravitational field. (I'm in high school so go easy on me, I'm just studying Einstein's Relativity for the general reader). For convenience let's keep with Einstein's example...
  36. M

    What exactly determines the energy of a wave? the intensity? or the frequency?

    I am taking AS level Physics rite now, and wanted to know what exactly determines the energy of a wave. Well since I have recently learn of stationary waves(sound waves) being standing. I know that they are formed by the superimposition of the reflected waves on the incident waves. This causes...
  37. A

    Need help to find intensity of waves.

    Homework Statement A tiny vibrating source sends waves uniformly in all directions. An area of 3.25 cm2 on a sphere of radius 2.50 m centered on the source receives energy at a rate of 4.20 J/s. (a) What is the intensity of the waves at 2.50 m from the source and at 10.0 m from the source...
  38. C

    Intensity Level of 76 trombones

    Homework Statement If the intensity level at distance d of one trombone is 70 dB, what is the intensity level of 76 identical trombones, all at distance d? Homework Equations β = (10 dB) log10(I/I0) I0= 1.0 x 10-12 W/m2 I = power/area The Attempt at a Solution 70db = 10db log10(I/I0)...
  39. F

    Estimate the relationship between the maximum and minimum intensity

    Two speakers A and B are separated by 1 meter, the point P is 4 m away from speaker B. If P is a person for what frequency does he hear that the intensity have a minimum?. (The listener hear that the sound intensity reduces and increases).I don't know the distance from P to B. (They form a...
  40. F

    For what frequency does the intensity have a minimum?

    Two speakers A and B are separated by 1 meter, the point P is 4 m away from speaker B. If P is a person for what frequency does he hear that the intensity have a minimum?. (The listener hear that the sound intensity reduces and increases).I don't know the distance from P to B. (They form a...
  41. F

    Saturated absorption: decrease size of material rather than intensity of light?

    In saturated absorption, the decrease in absorption (and corresponding increase in wave transmission) is dependent on the intensity of the incoming wave. But why can't we decrease the size of saturable material, rather than the intensity of light? According to my understanding, saturable...
  42. M

    Pressure Amplitude and Decreasing Intensity

    When a point source emits sound, the sound travels away from the source as a series of wavefronts - all being spherical shells - away from the source right? Now, we say the energy is conserved if we neglect damping forces in the medium, and so the power delivered by the source should be...
  43. T

    Calculating Electric Field Intensity at (0, 0, z)

    Homework Statement Electric charge of density ρℓ = 5 μC/m is distributed along the arc r = 2 cm, 0 ≤ ∅ ≤ ∏/4, z = 0. Find the electric field intensity at (0, 0, z) Homework Equations dE=(dQ(r)/(4∏ε(r^2))) (unit vector R)The Attempt at a Solution Letting pL be the charge density, letting r^2 =...
  44. M

    Finding the intensity of radiation ?

    I have a 150 W Xenon lamp with me and I need to know what is the intensity(W/m^2) of light being radiated on a surface at x distance away . How do I do it ? Can I use a photodiode, if yes then how ?
  45. S

    Intensity of Cu K-alpha radiation (excitation voltage)

    Hello there folks, I have some materials science HW I would like some help with. I need to find the intensity of Kα radiation based on the equation: I_Kα = Bi(V_A - V_K)^1.5, where B is a machine dependent parameter, i is the tube current, V_A is applied voltage, V_K is excitation voltage. Also...
  46. D

    Sound Intensity Level and Hearing Problem

    Thank you for the help!
  47. H

    Relationship between light intensity and current

    I'm doing a solar cell characterization project. But due to some fault in my solar simulator(I'm getting different results from another set up), I'm now figuring a way to check the intensity of light shone by my simulator on cell. I'm trying to obtain it from the corrected data of my cell (Isc...
  48. edguy99

    Observed intensity of Persistent Lines of Neutral Hydrogen

    The site http://physics.nist.gov/PhysRefData/Handbook/Tables/hydrogentable3.htm shows the intensity of various photon energy values from hydrogen. I was not able to see how this intensity was observed (ie. was it from a specific experiment, or does one simply look at the sun and count photons...
  49. N

    Calculate the Sound intensity level

    Homework Statement A jackhammer with a sound power of 10 W is operating in the countryside. Calculate the intensity levels at distances of 2.0 m and 50.0 m from the jackhammer. Calculate the corresponding levels in dB. Homework Equations β = (10dB) log (I/Io) where, β = sound...
  50. G

    Exploring Organ Pipes: Standing Waves and Sound Intensity

    hi could somebody explain to me how organ pipes work? so far, i figured out that there are standing waves in an organ pipe, that are determined by the length and the question of whether there is a closed or open end. but what determines the intensity between these possible frequences(e.g...
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