What is Intensity: Definition and 964 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. S

    Light intensity of a flashlight?

    Homework Statement A flashlight lights up a wall a distance L from the small bulb whose wattage is given by W. The conical beam emerges from the flashlight at an angle theta. What is the intensity of light as it hits the wall a distance L from the bulb? Homework Equations I = Power/Area...
  2. W

    Gravitational field intensity (help)

    I have this assignment in physics class and I'm stuck on this 1 question. What we were doing: We were hanging 0.10kg, 0.20kg weights etc.. on a Newton scale and we were recording the force of gravity. For 0.10kg I recorded 1 N, 0.20kg was 2 N, and so on until 1kg was 10 N. So the question...
  3. Pengwuino

    Working with Lasers: Safety Procedures & Intensity

    For a certain sexah project I'm going to do, I have a bunch of lasers that have an intensity of "<5mW". I have 780nm IR lasers and 650nm red lasers. When i made a lazy hookup to a 3V power source, the red laser was briiiiight which leads me to believe I've only ever used <1mW lasers in our labs...
  4. R

    What is the formula for calculating radiant intensity from an LED onto a body?

    Hi, I’m hoping some genius can help me out here. I’m trying to determine how many joules of energy per square centimeter (from an LED) are radiated onto a body given the following parameters. LED radiant intensity = 80mW/Sr LED diameter = 5mm LED beam +/- 20 degrees Wavelength = 880nM...
  5. K

    Relationship between electric field intensity and potential

    I find that there are two ways in which the relationship between electric field intensity and potential are expressed as mentioned hereunder: (A) E = - dV / dx (V = potential and x is the direction along which V varies) (B) E = - Delta V / Delta x My understanding of the application of...
  6. T

    Intensity and Power of isotropic sound

    Homework Statement An electronic point source emits sound isotropically at a frequency of 3000 Hz and a power of 34 watts. A small microphone has an area of 0.74 cm2 and is located 158 meters from the point source. a) What is the sound intensity at the microphone ? b) What is the power...
  7. R

    Need help w/ problem: Sound intensity and energy

    Homework Statement A fan at a rock concert is 30 from the edge of the stage. The sound intensity level at the edge of the stage is 110 dB. The fan's eardrums have a diameter of 8.4 . How much energy is transferred to each eardrum in one second? (Hint: It may help to asume that the speaker is...
  8. K

    Standing waves and maximum intensity?

    Homework Statement "Two loudspeakers emit sound waves along the x-axis. The sound has maximum intensity when the speakers are 27.5 cm apart. The sound intensity decreases as the distance between the speakers is increased, reaching zero at a separation of 60.5 cm. What is the wavelength of the...
  9. E

    Mean Intensity Magnitude of Variable Star

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  10. J

    Light Intensity Homework: Solve for Unknown Intensity

    Homework Statement A 60-cd lamp and a lamp of unknown intensity are placed 3m apart. A light meter is moved between the two lamps until it reads the same illuminance from both lamps. The light meter is then 1.5 m away from the 60-cd lamp. What is the intensity of the other lamp? Homework...
  11. I

    Electric Field Intensity and Potential Difference

    Homework Statement A man walks into an electric field with a small charged object that has a charged value of 4.2 E-6C. At a distance of 10m from the object that is responsible for the electric field, he notices a force of 8.0 N on the object he is carrying. What is the electric field...
  12. Z

    Understanding Intensity and Energy Relationships

    This is a sentence in my textbook: " E=hf Do not be misled by this equation: This equation gives the energy per photon. It turns out that if we double the fequency, we also double the number of photons increasing the intensity by a factor of four as expected. " I do not understand this...
  13. C

    Light Intensity Lab: Solving Junior Assignment w/ 3-Page Write-Up

    Hi, I'm a junior and I have been assigned a lab that I has completely me blown away! We are to find the intensity of our given light source on a solar panel at different distances. My partner and I understand how to complete the lab, but there is another part of the grade. We are assigned to...
  14. V

    Can Initial Intensity Differ from Incident Intensity?

    Homework Statement In the equation Beta=10log (I/I (initial) is the I inital always the incident intensity 10^-12? Or if you are moving from one intensity to another, then can the initial intensity be the one you were initially at? For example, if you were moving from an intensity of 5 to...
  15. I

    Frequency, Velocity, Voltage, and Intensity

    Homework Statement I have to calculate the frequency of incident light shot at a metal plate.Homework Equations I know the voltage, intensity, and wavelength. wavelength = velocity/frequency frequency = velocity/wavelength voltage = current • resistanceThe Attempt at a Solution There isn't any...
  16. W

    Difference between intensity and power

    Is there a difference between power and intensity? From some of the literature read(from laser specification), the impression given to me is that power is defined rather as determined over a particular beam spot size(area quantity) while intensity is defined as a quantity that is varied with...
  17. F

    Fluid Mechanics Pressure Intensity Diagrams

    I was wondering if anyone could please explain what an intensity diagram would look like if you had a layer of fresh water ontop of x amount of meters of salt water (or vice versa). What is the concept behind this? How could you draw it? The question keeps popping up in past exam questions but i...
  18. L

    Intensity of Double Slit Pattern

    Homework Statement Could anyone help me to explain how the intensity of the double Slit pattern works because I'm looking at the formula and I'm really confused...Homework Equations I=4Icos^2(phi/2) A=2Ecos(phi/2)The Attempt at a Solution
  19. P

    Why Is Wave Intensity Proportional to the Square of Amplitude?

    Homework Statement Q. Explain why the intensity of a sound or light wave is proportional to A^2, where A is the amplitude of the wave. Homework Equations S = (1/μ_0)ExB ... Poynting vector S = (1/μ_0)EB B = E/c E = Asin(kx - ωt) The Attempt at a Solution Hi everyone, So, for...
  20. W

    How Loud Are Seven Clarinets Compared to One?

    Homework Statement if one clarinet is playing a note at a sound level of 60 dB, what is the sound intensity of 7 clarinets playing identically at one time? Homework Equations is B=(10dB)log(I/Io) relevant to this? The Attempt at a Solution I just need to be pointed in the right...
  21. O

    How Does a 2.80 dB Difference Affect Sound Intensity?

    Homework Statement Two sounds differ in sound level by 2.80 dB. By what factor is the one intensity greater than the other? Homework Equations The Attempt at a Solution Is the equation B = 10dB log(I/Io) relevant?
  22. C

    Calculate Ambient Noise Intensity Increase: 86.0 dB - 85 dB

    A machinist is in an environment where the ambient sound level is of 85 dB, i.e., corresponding to the 8 Hours/day noise level. The machinist likes to listen to music, and plays a Boom Box at an average level of 86.0 dB. A.Calculate the INCREASE in the sound level from the ambient work...
  23. T

    Help on designing a device to measure light intensity

    Homework Statement I have been asked to design a device or assemble existing devices that will measure light intensity from a source across diifferent places on a table, the data has to be recorded electronically on a computer as well, the position of the measuring point has also to be...
  24. V

    Intensity of EM radiation for two incoherent waves?

    Homework Statement Two incoherent EM waves of intensities 10I0 and 14I0 travel in the same direction in the same region of space. What is the intensity of EM radiation in this region? Homework Equations I = I1+I2 + 2√(I1I2) or I = I1+I2 - 2√(I1I2) The Attempt at a Solution I...
  25. P

    Calculating Average Intensity of a laser blackboard pointer

    Homework Statement A laser blackboard pointer delevers 0.10-mW average power in a beam 0.90 mm in diameter. Homework Equations a) Find the average intensity. b) Find the peak electric field. c) Find the peak magnetic field. The Attempt at a Solution ok for part a) i used...
  26. X

    Calculating Sound Intensity and Level of a Whisper

    Homework Statement What is the sound intensity of a whisper at a distance of 3.0 m, in W/m^2 ? What is the corresponding sound intensity level in dB? Homework Equations I=P/4*pi*r^2 The Attempt at a Solution I tried looking up what the power of a whisper was and I can't find...
  27. J

    Elevator problem: energy, power, intensity,

    Homework Statement Question: An Elevator and its load have a mass of 1200 kg. a) what energy must be supplied to lif the elevator and its load ot a height of 100m? Answer: E = _________ Joules b)If the elevator rises at a speed of 5 m/s, how long does it take to cover 100m? Answer t=...
  28. Deneb Cyg

    Diffraction gratings and intensity

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  29. H

    Unpolarized Light Intensity problem

    Homework Statement Unpolarized light has intensity 15W/m^2 and is incident on a sheet of polarizing material whose transmission axis makes an angle of 25 degrees with the vertical. A second polarizer, whose transmission axis is horizontal, is located just past the first. (a) What is the...
  30. A

    Function to model intensity change over rotation

    Dear all: If I have a white light source which is at the positive infinite, and there is a plane receiving the light. Assuming that the plane is facing to the light source at the beginning. If I start rotating the plane, and keep recording the intensity of one point of the plane, what...
  31. N

    The intensity of the Sun and heat on Earth

    Hi all. Is the explanation for the fact that it is hotter at equator than other places at the Earth that the intensity of the Suns waves are greater at equator, since the number of beams per area is larger (since they are not scattered that much because of the lack of curvature)? I hope...
  32. T

    3 pieces of Polaroid sheet (light intensity)

    Homework Statement Unpolarized light of intensity I0 passes through two pieces of Polaroid sheet. The second piece is rotated so that the intensity of the transmitted light goes to zero. A third piece of Polaroid is inserted between the two pieces. Calculate the intensity as a function of...
  33. G

    How Is Laser Beam Intensity Calculated?

    Homework Statement A helium-neon laser of the type often found in physics laboratories has a beam power of 3.50 mW at a wavelength of 633 nm. The beam is focused by a lens to a circular spot whose effective diameter may be taken to be equal to 2.00 wavelengths. Calculate the intensity of the...
  34. V

    Intensity of the incident light

    Homework Statement Unpolarized light is incident on a system of three polarizers. The second polarizer is oriented at an angle of 33.0° with respect to the first and the third is oriented at an angle of 45.0° with respect to the first. If the light that emerges from the system has an intensity...
  35. D

    Variation in electrical lines of forces with intensity.

    This is what a book says - “The number of lines per unit area through a surface perpendicular to the lines is proportional to the magnitude of the electric field in that region. Thus, the field lines are close together where the electric field is strong and far apart where...
  36. Y

    How Does the Human Eye Detect the Dimmest Starlight?

    hi there. there's an example in the book, but I'm having a little trouble here. Homework Statement Assume that the human eye can pick up as few as 9 photons/s in the visible range. Based on this, estimate the intensity of the dimmest star that can be detected by a night-adapted eye. What...
  37. K

    Intensity of a laser through a converging lens

    Homework Statement A laser beam passes through a converging lens with a focal length of 19cm. At what distance past the lens has the laser beam's intensity increased by a factor of 6? Homework Equations I=\frac{c\epsilon_0 E_0^2}{2} ?? The Attempt at a Solution To be honest, I'm...
  38. P

    Intensity of transmitted light

    Homework Statement Two sheets of polarizing material are placed with their transmission axes at right angles to each other. A third polarizing sheet is placed between them with its transmission axis at 46° to the axis of the first one. (a) If unpolarized light of intensity I0 is incident...
  39. P

    What is the intensity of the incident of light?

    Homework Statement Unpolarized light is incident on a system of three polarizers. The second polarizer is oriented at an angle of 28.0° with respect to the first and the third is oriented at an angle of 45.0° with respect to the first. If the light that emerges from the system has an...
  40. D

    Does the size of a test charge affect the overall force in a charged field?

    The intensity of the test charge should be very less cause it will disrupt the field. Question is will it matter even if it disrupts the field? Consider 2 point charges q1 and q0 (take this as the test charge), as the intensity of 2 increases, so does the magnitude of force that applies on...
  41. D

    What is the Light Intensity 3 Meters from the Bulb?

    stuck on light intensity problem... 1. Homework Statement http://s685.photobucket.com/albums/vv212/dewdr0p714/?action=view&current=physicsexam2q5withoutphotocell.jpg A conducting rod slides down 2 frictionless copper tracks at a constant velocity. There is a .50 T magnetic field...
  42. I

    Intensity of Electromagnetic Wave

    Homework Statement Show that intensity of radiation(EM wave) falls off with depth z as I(z)= Ie^(-2niwz/c) where I = initial intensity and ni=complex paert of refractive index Homework Equations I have tried the solving the solution using poynting vector. I have been...
  43. A

    Is this correct. Intensity and sound level.

    Homework Statement A certain sound wave has a measured intensity of 40 decibels at a distance of 125 m from the point source where the waves originated. At what distance from the source would the intensity be increased to 70 decibels. Homework Equations Sound Level (B) = 10 decibels...
  44. K

    Photoelectric effect experimental data current vs. intensity vs frequency

    The photoelectric current is known to be directly proportional to the intensity of incident light with fixed frequency. Questions: 1) What are the experimental values of this proportionality constant for various fixed frequencies? 2) Is there a theoretical derivation that provides a formula...
  45. D

    How Is Sound Intensity Calculated at Different Distances from a Trumpet?

    Homework Statement When playing fortissimo (very loudly), a trumpet emits sound energy at a rate of 0.800 W out of a bell (opening) of diameter 12.7 cm. (a) What is the sound intensity level right in front of the trumpet? (b) If the trumpet radiates sound waves uniformly in all...
  46. M

    Need help to gradually ramp up/down intensity of LED at power-on/power-off

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  47. Y

    Physics3, question on intensity, power, wavelength

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  48. A

    Muon beam intensity and distance

    Homework Statement How far will a beam of muons with kinetic energy (a) 1 MeV, (b) 100 GeV travel in empty space before its intensity is reduced by half? Homework Equations See below The Attempt at a Solution My main problem with this is that it looks like we won't be taught the...
  49. Z

    Specific Intensity, Flux, Flux Density, Radiative Transfer

    Hi, I'm new to the technical aspects of astronomy and I'm having trouble quantifying what the definitions of some of these terms are. I can find equations that relate most of them, but I'm not sure how to use any of them. The terms are specific intensity, flux, flux density, and monochromatic...
  50. S

    Thesis Help Sound Intensity Probe.

    Thesis Help! Sound Intensity Probe. My final year thesis is to implement a sound intensity probe in MATLAB using two conventional microphones. Using these microphones, i can make recordings of audio to analyse in MATLAB, with the main aim to locate the sound from the phase information, and to...
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