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. D

    Percentage Change in Sound Intensity - Help

    Homework Statement An intensity level change of +2.00 dB corresponds to what percentage change in intensity! Homework Equations B = dB = 10 log (I/Io) The Attempt at a Solution 2.00 dB = 10 log (I/Io) 0.2 = log (I/Io) I/Io = 10e0.2 = 1.585 Assuming Io = 1, then percentage...
  2. D

    Sound Intensity Problem of 3 Machines

    Homework Statement In a factory, 3 machines produce noise with intensity levels of 76 dB, 82 dB, and 85 dB. With all three running, what is the intensity level? Homework Equations B = 10 log (I/Io) The Attempt at a Solution B = 10 log (10e7.6 + 10e8.2 + 10e8.5) I do not know...
  3. S

    Force from intensity of light

    Homework Statement The intensity of light from the Sun is 1.3 kW/m^2 at the distance of the Earth. The Earth’s radius is 6.4 × 10^6 m. If all the sunlight that hits the Earth were absorbed, what would be the magnitude of the resulting force on the Earth? Homework Equations F=IA/c...
  4. G

    Intensity in a point from two slits

    You have one slit which it is sent light through and in one point at a screen they measure the intensity with adding all the intensities from different rays who has different angels at the point. The E in the point is found from adding the E from all the rays and then you can find the intensity...
  5. O

    What are the steps for reducing sound intensity by 20 decibels?

    Homework Statement A man stands 3m from a siren. How far does he have to move to reduce the intensity level by 20 decibels? Homework Equations Intensity level = 10log(I/Io) the inverse square law The Attempt at a Solution i know the answer is 30m because 10 times the distance drops...
  6. M

    Measuring Magnetic Field Intensity (H) and Magnetic Flux Density (B).

    Now here is a real world practical application. Australia Post has a warning for shipping magnetic material in the post. Section D2.9.2 states... Any material that, when packed, has a magnetic flux density of 0.159 A/m or more at a distance of 2.1 meters from any point on the surface on the...
  7. P

    Sound Intensity of a microphone

    a) A microphone has an area of 3.8 cm^2. It receives during a 2.87 s time period a sound energy of 4.2x10-11 J. What is the intensity of the sound? b) Using the intensity in the previous question, what is the variation of pressure in the sound wave if the speed of sound is 343 m/s and the...
  8. M

    X-ray Diffraction, Intensity vs. Wavelength Graph

    Homework Statement http://b.imagehost.org/0607/Question_7.png Homework Equations [PLAIN][PLAIN]http://d.imagehost.org/0813/Untitled_6.jpg The Attempt at a Solution I was able to get question b, which ends up being 73pm, but as for questions a and c, I was unable to come up with...
  9. G01

    Why Does Inhomogeneous Media Saturate More Slowly in Laser Technology?

    Hello All, I'm going through some lecture notes from a course on Lasers, and have come across something that is confusing me. In homogeneously broadened media, the gain coefficient depends on (1-I/I_s)^{-1}. where I_s is the saturation intensity. However, in an homogeneously broadened media...
  10. T

    Plotting Intensity in Airy Pattern of Telescope - 1D

    How would I come up with an equation (in one dimention), for the airy pattern of a telescope with a given diameter observing at a given wavelength? something that looks like this http://upload.wikimedia.org/wikipedia/commons/9/93/Airy_Pattern.svg I want to be able to plot Intensity in the...
  11. N

    How do I calculate diffraction intensity for a 2D lattice?

    Homework Statement How do I figure out the intensity of diffraction spots after doing Bragg diffraction on a particular 2D lattice? Homework Equations The Attempt at a Solution I'll guess I make 1 spot in the diffraction pattern the strongest, and the diffraction spots around it...
  12. X

    What is the resulting intensity maximum at a minimum?

    Homework Statement Surprisingly, large interference effects can occur even when one of the interfering sources is not very probable. In the two-slit interference experiment, if one slit is “stopped down” so that the intensity of the wave getting through is reduced by a factor of 100...
  13. M

    Polarized Light Reflection: Solving for Intensity

    [b]1. A person riding in a boat observes that the sunlight reflected by the water is polarized parallel to the surface of the water. The person is wearing polarized sunglasses with the polarization axis vertical. If the wearer leans at an angle of 17.0 degrees to the vertical, what fraction...
  14. B

    Emission spectral line intensity

    Dear all I need to calculate the intensity of the spectral line. I have data from NIST website: wavelength, Aki (Einstein coefficient), gi, gk, Ei and Ek energy levels. How do i go about Thanks for your help
  15. C

    Light Fringes Change When Intensity of One Slit is Reduced

    Monochromatic light passes through two slits and produces light and dark fringes on a screen. Initially, the light from the two slits is of equal intensity. The light from one slit now had its intensity reduced. The intensity at the other is unchanged. What changes if any will occur in the...
  16. J

    Measuring solar storm intensity

    I just discovered about solar storm named "Carrington Event"; I'd like to know how such a solar storm could affect my PC today. I found some publications: http://www.bu.edu/csp/EMMREM/papers/carrington.pdf...
  17. T

    What Is the New Sound Intensity Level After a 2000-Fold Increase in Power?

    Homework Statement A sound wave is measured to have a 20-decibel sound intensity level (SIL). And the sound wave power flux (measured in Watts/m2) is then increased by a factor of 2000. What is the new sound level (in decibels) after this factor of 2000 increase in sound power? Homework...
  18. C

    Spatial Light Modulator to remove high intensity light

    Is there a way to use a Spatial Light Modulator or other device to remove high intensity light without removing low intensity (low amplitude) light from a physical object you are observing? High intensity light would be completely filtered (removed) but low amplitude waves would not be...
  19. D

    How Do You Calculate Light Intensity After Passing Through Water?

    I need to calculate the intensity of a 10000 lux light source traveling through 3.3 cm of water. I have attempted to solve this using the equation I=Ioe-A where i is the intensity, Io is the initial intensity, A is the absorbance calculated as the water attenuation coefficient times the...
  20. P

    Finding Electric Field intensity

    Homework Statement A proton traveling along the x-axis is slowed by a uniform electric field E. At x = 20 cm, the proton has a speed of 3.5 x 106 ms-1 and at x = 80 cm, its speed is zero. Find the magnitude and direction of electric field intensity. Can someone please! check my procedure...
  21. A

    Understanding Electric Field Intensity of Point Charges

    Why do we take a point charge always while estimating the electric field intensity of a system of charge? as in Coulomb's and Gauss's Law etc.
  22. Z

    Intensity of periodic sound waves

    Homework Statement A firework charge is detonated many meters above the ground. At a distance of 400m from the explosion, the acoustic pressure reaches a maximum of 10.0 N/m2. Assume that the speed of sound is constant at 343 m/s throughout the atmosphere over the region considered, that the...
  23. R

    Conversion Formula for Intensity Units: SI to AU Explained

    I know that the SI unit of Intensity is W/m^2. I came across one more unit of intensity -> AU..but could not get much on that. Can anybody tell me the conversion formula ( from SI to AU ) ?
  24. A

    Intensity of light vs amplitude

    Hi all, It is common knowledge that unpolarized light, when passing through an ideal polarizer, suffers a drop of half its original intensity. But since intensity is proportional to square of the amplitude, can we then infer to say that the new amplitude of light through the polarizer is...
  25. R

    Intensity & Amplitude of Gaussian Beam

    Can tell me the exact relationship between the intensity and the amplitude for a gaussian beam ? I know that I is proportional to |A|2 .. but i want the value of this proportianality constant
  26. J

    What is the Intensity of Light from a Cylindrical Source?

    I'm working on a project and don't have access to a physics book so I'm asking for help. I need to find the intensity of light at a certain distance over a given rectangular area from a cylindrical light source. The source is 18in long, 1in in diameter, and outputs 2.6watts. I need the light...
  27. P

    E-field of a laser pulse and Intensity

    Hi, What is the equation for a E field of a single pulse of a laser? If that laser is shined onto say a grating spectroscope (square law detector), how can I go about deriving an expression for Intensity as a function of frequency at the output of the spectroscope? I know that the square...
  28. N

    Relative intensity of polarized and unpolarized light in incident beam

    [b]1. A beam of light is a mixture of polarized light and unpolarized light. When it is sent through a Polaroid sheet, we find that the transmitted intensity can be varied by a factor of five depending on the orientation of the Polaroid. Find the relative intensities of these two components of...
  29. L

    F number and light intensity

    Homework Statement using the same film and level of illumination two pictures are taken, one with double the f number of the other. for both films to receive the same total light energy, what factor must the required time of exposure change for the picture with double the f number...
  30. D

    Understanding Wave Intensity and Superposition

    Statement: 1. The intensity of wave A at point P is I. Intensity of wave B at point P is (4/9)I. The phase difference between these two waves 180 degrees. Wavelength of A and B is 3x10^-4 and 2x10^-4 cm respectively. Frequency of both waves is "f". What is the resultant intensity at P in terms...
  31. U

    Answering MCQs on Sound Amplitude and Intensity

    Homework Statement Hi All, I have two MCQ, I could not answer them. All choices seem to be close to each others. I would be so grateful if you could help me. When the compression and expansion is very rapid, the sound is said to be high in: a) amplitude b) pitch c) frequency d)...
  32. N

    What is the Intensity Distribution in Young's Experiment with Light?

    If you disregard the diffraction pattern, the intensity distribution of the Young experiment with light (take two slits) gives an infinite intensity (in the sense that it doesn't decrease for an infinite height: the intensity distribution is given by a cos² function with a constant amplitude)...
  33. B

    How Do You Calculate Cooking Intensity from Cooling in an Oven Cycle?

    I have a block of food in an oven and I want to calculate the "cooking intensity" of the block during a controlled oven cycle. The cycle of the oven is that it heats at 5 degrees (C) per minute, holds the temperature at 300C for 1 hour, and then shuts off the oven to cool to room temperature. I...
  34. T

    Factors influencing signal intensity in MRI

    hi there i was wondering if you could help me: • explain the factors influencing signal intensity in MRI this is one of the questions in my assignment i was wondering if you could please help me ASAP as I am completely confused!
  35. V

    LED Intensity: Voltage & Band Gap Theory

    Hi guys, first post here but I have been looking around a while and this forum has proved to be pretty helpful. I have a question about LEDs. I just did a lab in school where I cooled LEDs by placing them close to liquid nitrogen and also heated them close to hot water and measured their voltage...
  36. R

    Rock Concert vs Whisper: Intensity Factor of 22026.4

    Homework Statement By what factor is the intensity of sound at a rock concert louder than that of a whisper when the two intensity levels are 120 dB and 20 dB respectively? Homework Equations The sound level of a sound wave in decibles is \beta = 10 log (\frac{I}{I_0}) Also the...
  37. S

    Diffraction Grating and Intensity

    Homework Statement Show that the maximum intensity for a diffraction grating of N slits at the first principal maximum is N^2 times bigger than for a single slit. Homework Equations I=I(0)[sin^2(NB)/sin^2(B)] where B is (\pidsin\phi)/\lambda The Attempt at a Solution I feel i...
  38. P

    Sound intensity level of a jet

    Homework Statement A jet traveling overhead at an altitude of 5000 feet produces a sound intensity level of 80 dB. What would the figure be for an eight of 1000 feet? Homework Equations The Attempt at a Solution
  39. C

    A multichoice question on intensity

    Homework Statement A plane wave of amplitude A is incident on a surface of area S placed so that it is perpendicular to the direction of travel of the wave. The energy per unit time reaching the surface is E. The amplitude of the wave is increased to 2 A and the area of the surface is reduced...
  40. P

    Calculating the epislon ε and current intensity? help please

    Homework Statement a battery connected to a light bulb that has electrical resistance of (6 Ω) and the current intensity that gets through the bulb counts (12 A), if the internal resistance of the battery was (2 Ω):- 1- what is the Driving force of the battery (ε)? 2- if the light bulb was...
  41. fluidistic

    Max Intensity of 2 Waves: E^2(E_01 +- E_02)

    Homework Statement Show that the maximum intensity of 2 waves is worth (E_{01}+E_{02})^2 while for 2 waves out of phase by pi rad, it's worth (E_{01}-E_{02})^2. Homework Equations Not sure about intensity. According to my notes it's worth (U_1+U_2)(U_1+U_2)* where * denotes the complex...
  42. R

    Exploring Malus's Law & Light Intensity in 3 Polarizers

    Hello I am trying to understand Malus' Law and the Intensity of light. Let's say I have three polarizers. The first polarizer and the last polarizer have the same axis of polarization. The middle polarizer can be rotated to an angle \theta I know that Malus's Law for the intensity of light is I...
  43. C

    Calculating sound Intensity?

    During my lecture we were presented with this problem How much louder is the intensity of sound at a rock concert in comparison with the sound of a whisper, if the two intensity levels (in dB) are 120 and 20, respectively? What my professor said was that the rock concert was 100 dB greater...
  44. L

    Intensity of unpolarized light through two polarizers

    1. Unpolarized light with intensity 440 W/m2 passes first through a polarizing filter with its axis vertical, then through a polarizing filter with its axis 20.0 degrees from vertical. 2. Malus's Law 3. Ok, the intensity after going through the first polarizer should be 1/2...
  45. L

    Intensity of light with given power through a polarizer

    1. A 200 mW horizontally polarized laser beam passes through a polarizing filter whose axis is 25 degrees from vertical. 2. Malus's Law 3. Ok, so I will use theta = 65 degrees in the I = I0cos(theta) equation, right? But how do I calculate I0 knowing only power and not area?
  46. L

    Intensity of light through two polarizers and Malus's Law

    1. A beam of unpolarized light with intensity I_0 falls first upon a polarizer with transmission axis theta1 then upon a second polarizer with transmission axis theta2, where theta2 - theta 1 = 90 degrees (in other words the two axes are perpendicular to one another). What is the intensity I_2...
  47. J

    Calculating Sound Wave Intensity and Decibels 10.0m from Source

    A source of sound emits 5.0 mW of acoustic power uniformly in all directions. 1. Calculate the intensity of this sound wave 10.0 m from the source. 2. Find the sound level in decibles 10.0 m from the source. Answers: 1. 4 x 10^-6 W/m^2 ---- I don't know how to get this answer. 2. 66 dB...
  48. H

    Calculating Radio Source Intensity and Momentum

    Homework Statement At a distance of 25m from an isotropic 100 MHz radio source the intensity is 120W/m2. A) What is the rms electric field at 25m? The answer should be 213 V/m. B) Over a 2 hour period, what is the momentum given to a 4cm x 4cm surface (at the 25m distance)...
  49. N

    Understanding Intensity in Spectral Lines: A Brief Overview and Common Questions

    Can someone help me to clear out a few questions about Intensity from spectral lines. - I have seen in many reports the unit cm-2 atm-1? Where does this come from? - What is the differences between line strength and the absolute intensity if the spectral line? - If you measure light from...
  50. T

    Sound Intensity of a workplace

    Accoding to US government regulations, the maximum sound intensity levels in the workplace is 90,0 dB. Within one factory, 32 ihdentical machines produce a sound intensity level of 92,0 dB. How many machines must be removed to bring the factory into compliance with the regulation? Possible...
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