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. R

    Why Do We Use the Complex Conjugate of Velocity to Calculate Acoustic Intensity?

    Hello All, I would like to know why do we multiply the complex conjugate of velocity (not just the velocity) with the complex pressure to obtain the complex acoustic intensity. Could someone please help me with this? Regards, Radel...
  2. S

    Light Intensity Model: Showing Minimal Difference at Off Point

    Can someone assist with a simple model for the following question? I have looked on the net but cannot find anything on it. Say you are sat at a desk with the light bulb directly above you switched off and the rest on; so: on - on - on on - off - on on - on - on Each at distance r apart with...
  3. J

    Finding wavelength and intensity of a specific light

    Hi people not sure if this is feasible but this is the idea and like to hear your comments i wan 2 shine a specific color of light (could be colored LED, normal light,) to determine the wavelength n intensity of it, so i am thinking of using a photodiode and an opamp connected with a...
  4. N

    Double Slit Intensity Problem

    Homework Statement Coherent light with wavelength 585 nm passes through two very narrow slits that are 0.320 mm apart. The screen is 0.700 m away from the slits. The intensity is I0 at the centre of the central maximum (theta=0) (a) What is the phase difference (in radians) in the light from...
  5. X

    Calculating Average Emission Wavelength from Spectral Intensity Chart

    I haven't had calculus in over 2 years and so I am not exactly sure how to go about this. I am inclined to believe some form of integration would be needed. I took the chart below from a paper on LED wavelength emission. The authors say that the vertical line represents the average emission...
  6. K

    Intensity of polarized light that has passed through two polarizing sheets

    Homework Statement A beam of polarized light of intensity 43.0 W/m2 is sent through a system of two polarizing sheets. Relative to the polarization direction of that incident light, the polarizing directions of the sheets are at angles θ for the first sheet and 90 degrees for the second...
  7. ChrisVer

    Saturation Intensity and Power

    Hi, I am not sure if this is an easy question, but I've been looking around and I haven't been able to find some exact equation to this. I performed an experiment where I allowed for a laser beam to go through a cell (of Rubidium-85 and 87) and got the resulting spectrum. The initial [100%]...
  8. deedsy

    Spherical Charge Distribution - Electric Field Intensity

    Homework Statement A spherical charge distribution is given by p = p_0 (1- \frac{r^2}{a^2}), r\leq a and p = 0, r \gt a , where a is the radius of the sphere. Find the electric field intensity inside the charge distribution. Well I thought I found the answer until I looked at the back of...
  9. D

    Photoelectric exp - calculate intensity of incident light

    Homework Statement In an photoelectric effect experiment , a photoelectric current of 100µA is obtained when lights of 550nm is incident on metal cathode of surface area 1.0cm^2 ... calculate the intensity of the incident light. The ans is 2.26w/m^2 Homework EquationsThe Attempt at a Solution...
  10. C

    What is the significance of r in the intensity formula for a Gaussian beam?

    Hi!. I´m modeling a gaussiam beam. I found that considering the electric field distribution of Gaussian laser pulses along the axis of propagation, we can write the intensity as: Where y = I_l R is the power is the power reflection coefficient y = w_0 is the beam waist radius at y = z=0...
  11. S

    Solving Sun Intensity Problem: 685W/m^2 in 6.5 Days

    Sun emits 153.6 x 10^15 J of energy onto a region that is 20km by 20km in area. The intensity of the sun on this region is 685W/m^2. How many days would it take for the sun to put that amount of energy onto the region? I went intensity = power/area and got to a time of some 44000seconds...
  12. S

    What is the decibel level of a sound at 4% intensity of a 95dB sound?

    What is the decibel level of a sound whose intensity is 4% that of a 95dB sound? I know dB = 10log(I/Io) but don't know how to incorporate this for this question.
  13. S

    Intensity of light after passing thru polaroid

    Homework Statement Two pieces of polaroid are arranged so they are initially parallel . One of the polaroid is rotated until the intensity of the light beam from the two polaroid is 1/3 of its initial intensity . Calculate the angle turned thru the polaroid Homework Equations The...
  14. M

    Electric field intensity around a wire

    Homework Statement I am trying to calculate the surface charge density and electric field intensity around a copper wire. This is not a part of my assignment but out of curiosity. First, A current carrying wire of radius 2m, radius 0.5cm is at a height of 5cm above a ground plane, the ground...
  15. Chacabucogod

    Radiation Intensity Thermodynamics

    So I understand that a black body is a diffuse emitter, and that it radiates energy at a rate of σT^4. I also understand the correspondence between a solid angle and the superficial area of a sphere. dS=r^2sin(θ)dθd\phi=\frac{ds}{r^2}=d\omega=\frac{dAcos(\alpha)}{r^2} What I don't...
  16. Chacabucogod

    How Does the Cosine of an Angle Affect Radiation Intensity from a Black Body?

    So I understand that a black body is a diffuse emitter, and that it radiates energy at a rate of σT^4. I also understand the correspondence between a solid angle and the superficial area of a sphere. dS=r^2sin(θ)dθd\phi=\frac{ds}{r^2}=d\omega=\frac{dAcos(\alpha)}{r^2} What I don't...
  17. D

    Intensity of single slit and double slit problem

    For a double slit experiemnt, the bright fringe has intensity of I, when one of the slit is covered, the intensity is 0.25I. In my opinion, the slit now become single slit, so it has area of half of the initial area, but we know that power is the product of intensity x area, by keeping the...
  18. V

    Light intensity and wave behavior of light

    Hello PF'ers, Why is it that two light-bulbs produce twice as much brightness as a single light-bulb would? If we restrict our attention to a single point in space where light from the two sources meet, the waves would cancel half of the time and reinforce half of the time, producing on...
  19. Nero26

    Finding the charge density,when Electric field intensity is given.

    Homework Statement Given, E=ar20/r2 (mV/m) in free space,find ρv at the point (3,-4,1)(cm). where, ρv=Electric charge density per unit volume E=Electric field intensity Homework Equations ∇.(εE)=ρv The Attempt at a Solution ε∇.E= -2\frac{20ε}{r^3} for point (3,-4,1)(cm)...
  20. S

    Why Does Doubling Sound Sources Not Simply Double the Decibel Level?

    Homework Statement A source prodeuces sound of intensity level of 30dB .If another source prodeuces sound at the same time , what's the resultant level?Homework Equations The Attempt at a Solution the ans is 10 log (2##I_1## / (##I_0##)) = 33dB , but why not = 10 log (4##I_1## / (##I_0##)) ...
  21. S

    Frequency of varaiation of sound intensity

    Homework Statement A motorcyclist travel at cnstsant speed of 72km/h along a straight road toward an obesrver standing at the centre of bridge over the road . When the motor cyclist is distant, the obesrver hears a sound of 65hz from the engine of the motorcycle. What would be the frequency...
  22. S

    Factors affecting sound intensity

    Homework Statement the factor affecting sound intensity is amplitude and frequency . why not also the distance from the source (r) , in my opinion, intensity = power/area , so the intensity = power/ 4 pi r ^2 ... so I is inversely proportional to r^2 ... Homework Equations The...
  23. S

    Factors affecting sound intensity

    Homework Statement the factor affecting sound intensity is amplitude and frequency . why not also the distance from the source (r) , in my opinion, intensity = power/area , so the intensity = power/ 4 pi r ^2 ... so I is inversely proportional to r^2 ... Homework Equations The...
  24. shanepitts

    What is Specific Intensity in Astrophysics?

    I am currently autodidacting the basics of astrophysics, and I of course came across the term specific intensity. The book explicates that it is defined as the differential of intensity per frequency element. But is there a better explanation so that I could lean closer towards a visualization...
  25. Greg Bernhardt

    Definition of Intensity of Radiation

    Definition/Summary Intensity of radiation = power per area perpendicular to the radiation. It is a vector, parallel to the radiation. Intensity of radiation = energy density times velocity (therefore sometimes called energy flux). It is measured in watts per square metre (Wm^{-2})...
  26. D

    Wave intensity at different points

    Homework Statement here's the question , ans any my hand written working. which one is correct ? my ans or the model answer? Homework Equations The Attempt at a Solution
  27. D

    Intensity of circular waves

    Homework Statement when a stone is thrown to position O (in a pond), a wave is generated and the wave eventually spread out form the center, my question is will the amplitude of particle of A, B and C change? the wave intensity is I= 0.5m(w^2)(a^2)s^-1/ 2 pi r so i have i got I is...
  28. D

    Intensity of Waves: Proportional to y^2/x^4?

    Homework Statement since we know that the intensity of wave is I=P/A P =power, A=area so I = 0.5m(w^2)(y^2)/4pi (x^2 ) so i got I is directly propotional to (y^2)/ (x^2 ) but there's variable x in the eqaution of y... so can i say that I is directly propotional to y^2 / x^4...
  29. C

    Optical molasses at high intensity (forces in OL's)

    Hey there. My goal is to understand the origin of the main forces that keep together an optical lattice created by two identical counter-propagating laser beams. I quote a small excerpt about the forces in optical molasses with high intensity, which I'm having trouble in understanding...
  30. Y

    Intensity and frequence of light

    I have a doubt that can we increase the intensity of light without changing its amplitude and by increasing its frequency ? :what:
  31. F

    Sound intensity and speakers

    Homework Statement Three speakers with the same effect are connected to the same tone generator are placed along the y-axis and sends out sound in equal directions. The distance a and b are in the same magnitude as the wave length of the sound...
  32. A

    Poynting vector and intensity in scalar diffraction theory

    The power density of an electromagnetic wave is proportional to the absolute square of the electric field |E|^2 (assuming a plane wave). Here, E is a vector so the absolute square involves all three of Ex, Ey, and Ez. In homogeneous, linear media, it's easy to show that each component of E...
  33. J

    How Small Must a Bone Be to Detect a 5% Change in X-ray Imaging Intensity?

    Homework Statement Imagine a 10 cm thick slab of flesh. If your x-ray imager can reliably identify a 5% change in intensity from one location to another in an image, what is the smallest diameter bone you are going to be able to make detect in your x-ray image? Absorption length of bone...
  34. E

    Calculate the intensity of a solid object made up of point light sources?

    So I understand that to calculate the intensity a distance d away from a light-bulb you would treat the light-bulb as a point source and do a gaussian-sphere-type-of-thing to figure out the intensity at the desired location. My problem involves a solid object made up of "point" light sources...
  35. I

    Principle Determining the Loudness (Intensity) of Sound

    A test question I was asked earlier in the year has been hanging around in the back of my mind: "If a radio is moved 3x further away from you, how is its loudness affected?" To answer this question one needs to know what determines the loudness of sound. What determines the loudness of...
  36. A

    Finding gravitational potential and intensity in point A

    Homework Statement Here is the pic: http://i.imgur.com/olnuDjL.jpgHomework Equations The Attempt at a Solution So intensity was pretty easy, it came up to be y=\frac{GM}{a^{2}}(1+\frac{1}{2\sqrt{2}},1+\frac{1}{2\sqrt{2}}) Check on if it's correct would be nice aswell. Now for potential I know...
  37. R

    Intensity of natural light after polarization

    I read that if a beam of unpolarized light goes through a polarizer, the intensity of the polarized beam is equal to half the intensity of the original beam. Can someone explain me why? I thought the intensity would be the same.
  38. L

    MHB Light Intensity: A & B, Distance D, Minimal Point?

    the intensity of iturninacion at any point is proportional to Ia intensity of light source and varies inversely as the square of the distance from the source. if two sources, A and B intensities, are at a distance D, at what point on the line that joins them, thee intensity of Lighting will be...
  39. K

    How far can your voice carry at 40 dB?

    You are in a park when you spot your friend 100 m away. At what lowest decibel should you shout your greetings so that your friend can just hear you? Assume that your friend has normal hearing. My prof never gave an example of how to do this and I can't figure it out. The correct answer is...
  40. Maxo

    Resulting intensity of interference

    Homework Statement Two speakers with the same power output generate sound waves in 360 degrees direction. Both speakers have the same freuqncy and the distance between the speakers is given. How can we from this calculate the sound intensity at any given point around the speakers...
  41. G

    Light intensity through a slit

    Homework Statement After a laser beam passes through two thin parallel slits, the first completely dark fringes occur at ±14.0∘ with the original direction of the beam, as viewed on a screen far from the slits. A)What is the ratio of the distance between the slits to the wavelength of the...
  42. F

    Electric field intensity with a charge decreasing over time

    So a lossy dielectric sphere gets an initial charge distribution evenly across the sphere. Find an expression for E inside and outside the sphere for all t. I figured that σ∇E=dp/dt p being volume denity. So I apply spherical coordinates to the div of E and integrate over r to get...
  43. Z

    Intensity of isotropic sound waves

    Homework Statement A loudspeaker emits sound isotropically with a power of 100db. Find the intensity in w/m at a distance of 20 from the source Homework Equations Intensity=power/area, For sound wave... power=ro*a*2pi^2*f^2*v*A^2, and I=2pi^2*ro*f^2*v*A^2. db=10log_10_(I/I_0_)...
  44. C

    Intensity of a sound wave problem

    Homework Statement Two loudspeakers are placed beside each other and produce sound of the same intensity at the position of a listener. One speaker produces a low note of 40 Hz and the other produces a high note of 2560 Hz. What is the ratio of the maximum displacements of the speakers...
  45. P

    Intensity in double slit interference

    I'm a little confused about a small detail when finding the intensity over the screen, as some notes I'm using happen to calculate the same thing twice, with a slight difference the second time. Each method does the following Call the electric field at any point E so we have...
  46. S

    Intensity of single slit vs double slit

    Homework Statement Light of intensity I0 passes through two sets of apparatus. One contains one slit and the other two slits. The slits have the same width. What is the ratio of the out going intensity amplitude for the central peak for the two-slit case compared to the single slit?Homework...
  47. M

    Archived Intensity of coherent/incoherent light

    Here's a question I'm working on. I've managed everything uptil the first bolded part, then I get stuck there. I have no idea how to estimate the relative intensities of coherent and incoherent light. I've had a look at tonnes of formulas for the intensity of light but can't find one which would...
  48. D

    Intensity of Light understanding

    Homework Statement When light of wavelength 630 nm is directed onto a photocell, electrons are emitted at a rate of 2.6 *10 raised -12 C/s. Assume that each photon that impinges on the photocell emits one electron. How many photons per second are striking the photocell? How much energy per...
  49. J

    Overall Intensity of Destructively Interfering Waves

    If you have two sound sources emitting the same frequency and in phase with each other such that the emitted waves destructively interfere along the line containing the two sources, is the intensity at the points 0 or the sum of the intensity of each source independently?
  50. D

    Intensity for circular polarised light through linear polariser

    Hi, does the intensity change when circularly polarised light passes through a linear polariser? I am thinking of a flow like this: natural light -> vertical linear polariser -> quarter wave plate -> horizontal linear polariser -> intensity? After the first polariser, the intensity is 50%...
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