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. I

    Intensity in Young's double slit experiment problem.

    Hello all, I have a problem that requires some knowledge about Young's double slit experiment. The question is as follows: Imagine performing Young's experiment with one slit wider than the other so that the intensity passing the wider slit is four times as great as that passing the narrower...
  2. Amith2006

    Decrease in intensity of light on undergoing successive reflections

    Sir, 1) A thick plane mirror shows a number of images of the filament of an electronic bulb. It is said that of these images the first image is the brightest. Is it true? If so, is it because some energy is lost in traversing through the dense medium? 2) It is said that the...
  3. B

    Photoelectric Effect - Intensity in Phototube

    We have been doing some experiments using a mercury light source and filters for each wavelenght and a Detector Box (phototube) to measure the output voltage, to investigate planks constant, stopping voltage, intensity's effect... the typical - "energy is quantised" idea. :zzz: There is one...
  4. W

    Intensity of sounds - Hearing Aid

    A person wears a hearing aid, which makes a sounds louder by 50 dB. This a) means the sound intensity is increased by 100,000 times. b) This also means that the amplitude of the soundwave is increased by ______ times? I know Intensity is portportinal to (Amplitude)^2... so does that mean I...
  5. P

    Intensity of EM waves in a conducting medium

    I'm attempting to calculate the above, but I'm stuck. What I have thus far: intensity is the time average of the poynting vector, where the poynting vector is the cross product of the E and B fields. Using the given expressions, I get: \frac{\sqrt{a^2 + b^2}}{\mu \omega} E_0^2 \exp(-2bz)...
  6. U

    What is the convention for defining polarization direction in EM waves?

    I have a quick question about polarization. When I put a polarizer up an unpolarized source, say the polarizer blocks all the polarization in th y direction and so all the photons in the x direction comes out of the polarizer. Is the intesity halved? It seems to me that the intensity should...
  7. fargoth

    Laser intensity as a function of distance

    i built a laser in my lab... it consists of one Ne-He tube with a concave mirror at one end and a window at the other end. i just put another mirror infront of tube's window to get the laser. i got one question i can't find an answer to, the lab's guide said the intensity of the laser depends...
  8. L

    Fraction Of The Intensity Incident

    Two Polaroid filters are initially crossed. The analyzer is rotated through an angle of 55.0 degrees. Find the fraction of the intensity incident on the polarizer which passes the analyzer. I used I1=1/2 Io I2= I1cos I2= 1/2 Io cos^2(theta) = 1/2 Io cos227.5° = .393 Io Is...
  9. J

    Characteristic X-rays, intensity ratios

    Hi! What can be said about the intensity ratios of characteristic X-rays (Kalpha to Kbeta ) originating from a X-ray tube? I mean roughly and in general, not for some very specific anode material. I first thought that K-L (Kalpha) transitions would be more likely to happen than K-M:s...
  10. T

    Sunlight Intensity: Measuring for Window Facing South

    A research center measures sunlight intensity every hour every day. The measuring device stands on flat ground and therefore measures light accordingly. The output is W/m^2. The problem is that I need to utilize this value for a vertical window on a wall facing south. How can I best do this?
  11. T

    A pyranometer, a device that measures sunlight intensity

    I am to use a pyranometer, a device that measures sunlight intensity. I am confused about the output unit it produces. It says on it's side 4.55 \cdot V/\left( {W \cdot m^{ - 2} } \right) but I'm not sure how to interpret this unit. All help will be appreciated...
  12. C

    Energy in EM Waves problem (finding sun power output from EM wave intensity)

    Hi, if someone could help me figure this out I'd really appreciate it. Estimate the average power output of the Sun, given that about 1350 W/m^2 reaches the upper atmosphere of the Earth. I know the answer is 3.8 X 10^26 W but I don't know how to get there. I've tried different equations...
  13. 1

    Sunlight Intensity: Calculate Total Average Power Output of Sun

    I need help with this problem... Suppose that the intensity of the sunlight that reaches Earth's upper atmosphere is approximately 1200 W/m2. Earth is about 1.5 times 108 km from the Sun. What is the total average power output of the Sun, assuming it to be an isotropic source?
  14. I

    Intensity of stokes and anti-stokes lines?

    According to Raman effect, the intensity is directly proportional to the 4th power of the wavelength. Then how come stokes lines, which have higher wavelengths than anti-stokes lines, are more intense than the anti-stokes lines?
  15. R

    Light Intensity: Definition & Applications

    Hi, I just came to this problem when I was studying the photoelectric effect, what is the exact definition for "light intensity" ? Is it just n (the number of photons) or is it E/(A.t) where E=nhf ? The latter can be the same as the former in comparison when we suppose the frequency is the...
  16. S

    How Does Radiation Intensity from a Star Change with Distance?

    but somehow my brain is not working... how does the intensity of radiation emitted by a star (but really any hot sphere, really) vary with distance from teh star? at the surface the intensity is I = 4 \pi \sigma T^4 R_{star}^2 as we move away I = 4 \pi \sigma T^4 (R_{star} + r)^2...
  17. D

    Does Electric Field Intensity Stay Constant Between Charged Parallel Plates?

    Does the intensity of the electric field between two charged parallel plates stay constant regardless of the distance between the plates, assuming of course that the plate area is such that the plates do not become point charges?
  18. I

    Decibel / Intensity Problem, How do I approach it? .

    Decibel / Intensity Problem, How do I approach it? ASAP.! I have a question, I don't know how to approach it.. I couldn't find a way.. 1.Suppose that the sound level of a conversation is Initially at an angry 70 dB and then drops to a soothing 50 dB. Assuming that the frequency of the sound...
  19. U

    Intensity from a multi slit grating

    The intensity from a multi slit grating with 2N+1 slites is given by: I(Y)=\frac{M^2}{2R^2} \frac{sin^2 \left[(2N+1) \frac{x}{2}\right]}{sin^2 \left[\frac{x}{2}\right]} where x=\frac{2 \pi Y d}{D \lambda} I am to show how to find the limiting case of just two slites and show that in...
  20. U

    Wave Intensity: A^2(z,t) at (15 cm, .5s)

    the wave intensity is defined as the squared wave amplitude. I(z,t)=A^2 (z,t) A(z,t)=a cos [2 \pi (\frac{r}{\lambda}-\frac{t}{T})] the wavelength is 10cm period is 1/10s a=1mm 1. what is the instantaneous intensity at r=15cm and t=.5s? is the solution: A^2(z,t)=(.1 cos [2 \pi...
  21. S

    Finding Maximum Sound Intensity: How to Determine the Two Lowest Frequencies?

    Hello. I am totally stuck on this question. I don't even know where to begin. Any help would be appreciated: A spherical sound source is placed at P1 near a reflecting wall and a microphone is located at P2. The frequency of the sound source is variable. Find the two lowest frequencies for...
  22. Amith2006

    Circularly polarized light of intensity through a polariser

    Sir, A circularly polarised light of intensity I is passed through a polariser resulting in the production of plane polarised light.What is the intensity of the plane polarised light? What is the expression which governs this effect?The formula that I know is I' = I cos^2x(Mallus law).Here...
  23. A

    Finding electric field intensity of two spheres

    Any help on this question is appreciated. Two small spheres each of mass m are suspended by light strings of light L. A uniform electric field is applied in the x direction. If the spheres have equal and opposite charges of magnitude Q, determine the electric field intensity that enables the...
  24. electronic engineer

    Do I need to supply a 555 IC with 5V for a temperature intensity meter circuit?

    I've attached a circuit schematic for the temperaure intensity meter... R1 is the PTC the first 555 works as monostable so it triggers second 555 to produce Astable pulses with given frequency depending on the values(R3 and R3 and C4) anyway i want to ask if i have to supply my second...
  25. B

    How does power relate to intensity?

    In this problem you will use the decibel scale to analyze a small firecracker that emits 1200 W of peak power. How does I(the intensity) relate to 1200 peak power? THANKYOU!
  26. L

    Calculating Distance Between Two Speakers Producing 180Hz Sound in Phase

    Two speakers produce a 180Hz sound in phase. If an intensity is located 2.10m from the nearer spearker, find the distance to the further speaker if the speed of sound in the air is 345m/s. I don't understand exactly what this problem is asking for, and I can't find an equation relating these...
  27. F

    Light Intensity through glass blocks

    Hey dudes and dudettes, loving the forum here. Will be around quite a bit for the next year or so hopefully.. Just a quick question, any help would be appreciated so much.. I'm doing my A2 main coursework, that's the one you do when you're 18 for all the American types, and was wondering...
  28. electronic engineer

    Light Intensity Meter: Schematic, ICL7107, Eagle & More

    This is the schematic of my project (figure7)...but I don't know how to add display (ICL7107) using eagle, and how to power display .. how to connect the output voltage of stage2(second opamp) to the display? http://www.seas.upenn.edu/~ee205/Labs97S/Lab7/Lab7.html anyway , take a look at...
  29. D

    Sound loudspeaker intensity problems

    These questions are giving me some trouble: 6. A loudspeaker at a rock concert generates 1 x 10^-2 W/m^2 at 20 m at a frequency of 1.0 kHz. Assume the speaker spreads its energy uniformly in all directions. a. What is the intensity level in dB at 20 m? b. What is the total acoustic...
  30. S

    Sound Intensity of Piston in Engine at 8000 RPM

    consider a piston in an engine with a stroke of 86 mm and RPM 8000 which gives the frequency of sound it is producing(due to compression and decompression) to be 133 Hz and wavelength 2.57 m. Then the pressure amplitude turns out to be 20000 Pa and the intensity of the sound wave to be...
  31. S

    Magnetic field intensity questions

    I tried reading my textbookfor the answers to these questions, but I can't find an answer. Can someone answer these questions? 1. Changing the magnetic field intensity in a closed loop of wires induces A. Current B Voltage C. Both D. Neither 2. True or False: Energy emitted by...
  32. S

    Physics Help sound level intensity

    A person standing a certain distance from an airplane with three equally noisy jet engines is feeling a sound level intensity bordering on pain, 120dB. What sound level would this person experience if the captain shut down one engine? this is what I did: B-120=10log.33 and ended up with...
  33. H

    How to measure the Intensity of Light?

    While I and my friends were talking about some topics in optics, we come to realize that we do not know how to measure the the intensity of light. Does anybody have a good idea? I don't want to hear 'Oh, You use blah blah to measure the Intensity of light' but rather what's being directly...
  34. M

    A New look at the intensity of light.

    Suppose that you are an observer in a room equipped with only one window measuring 1 m sq. The window is glazed with a glass pane 1 cm. Thick. The only source of illumination is a green surface outside the window. Hence the only light entering the room is the green light from this surface...
  35. C

    Actual intensity of the sound

    If a large housefly 3 m away from you makes a noise of 40 dB, what is the noise level of 1000 flies at that distance, assuming interference has a negligible effect? Noise level of 1000 flies = ?
  36. O

    What is specific intensity anyway?

    Hi all, I need a hand regarding this problem, just can't seem to find the start point. (It's a two parter): What is the specific intensity of the radiation at the solar surface in the direction of Earth What is the specific intensity of solar radiation at the surface of the Earth. As...
  37. S

    Magnetic Field Intensity Question

    This is for an assignment that is due next Monday for me. I'm kind of confused here for how to calculate the magnetic field intensity at all points for the conductor(s) in the diagram I have attached. First, there is a cylindrical conductor of radius a, then surrounding it is another conductor...
  38. L

    How would light intensity and humidity

    affect the infiltration of water in the soil? :bugeye: Thank you thank you thank you.. :]
  39. O

    Flux vs Intensity in Astronomy

    Hey everyone! What is really the difference between flux and intensity in astronomy? What I understand they are two different words of the same thing, namely energy per square length unit per time unit. I appreciate any help, thanks alot!
  40. S

    Reflection Intensity: Iron vs. Hollow Black Box

    If monochromatic light of the same amplitude is shown on a closed hollow black box and a closed black box filled with iron, will there be a difference in the intensity of light that is reflected back due to differences in the absorption of light in the two boxes?
  41. D

    What is the Surface Charge Density on a Long, Uniformly Charged Cylinder?

    Hi, I would appreciate is someone could help me figure out this problem: The electric Field Intensity in free space from a very long, uniformly charged cylinder of radius 5cm is 100 kV/m at a radius of 1m. What must be the surface charge density on the cylinder? I've tried using different...
  42. E

    Double slit intensity - QM description

    Hello, I wondered how one treats the double slit experiment quantum mechanically, that is, using probability amplitudes,wave functions,etc...to calculate the intensity on the screen. If anyone knows a link or a paper or a book where I can find it, that'd be nice. -Edgardo
  43. P

    Electric field intensity for a uniformly charged wire.

    A uniformly charged wire with a charge density of p (rho) extends along the z-axis from z = 0 to z =+ infinity. Determine the electric field intensity at a point P (rho, phi, 0) Ok so I wrote down the equation for electric field intensity for a uniformly charged wire ie E=k[integral of...
  44. B

    How Far Must a Helicopter Fly to Decrease Sound Intensity by a Factor of 4?

    I am confused about a homework problem and was hoping that maybe somebody here can help... Homework Problem When a helicopter is hovering 1090 m directly overhead, an observer on the ground measures a sound intensity I. Assume that sound is radiated uniformly from the helicopter and that...
  45. C

    Answer: Intensity Outside a 43.5 dB Quieter Room

    A recording engineer works in a soundproofed room that is 43.5 dB quieter than the outside. If the sound intensity in the room is 1.00 10-10 W/m2, what is the intensity outside? Here is how I THINK I should be solving this problem. Intensity level = 10dB * log ( I / Io) Intensity...
  46. Y

    Sound Intensity Level Question

    :confused: A loudspeaker supported well above the ground on a post is supplied with 8.5 W of electrical power. The speaker is able to convert 5.6% of that into sound power. (That number is known as the speaker's efficiency.) If we assume that sound radiates equally in all directions...
  47. F

    Finding Amplitude of Air Vibration from Frequency and Intensity

    I'm given two things: frequency, f = 313 Hz intensity, I = 1.13 uW/m^2 (microWatts per square meter) I'm supposed to find the amplitude of the air vibrations caused by this sound. As always, a push in the right direction is greatly appreciated.
  48. B

    SI unit for luminous intensity

    This is the SI unit for luminous intensity. The definition relates to blackbody radiation emitted at a certain temperature for a certain material (so I guess it ISN'T blackbody!), platinum, I think. Except... I don't understand the necessity for the introduction of this unit. Isn't...
  49. S

    Mathematica Understanding Impulse, Intensity & Inertia

    Could someone explain to me the mathematical differences between impulse, intensity, and inertia? I mean, they all start with I's, but I still cannot determine any mathematical precision instead variation among these three.
  50. S

    Intensity of laser beam / Inverse square law

    Hello everyone! I'm having a real tough time with this one, maybe I can get a little help. A small helium neon laser emits red visible light with a power of 3.2 mW in a beam that has a diameter of 2.5mm. What is the intensity of the laser beam? Does this intensity obey the inverse square...
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