Questions tagged [intensity]
207 questions
73
votes
3 answers
How strong are Wi-Fi signals?
My family members dislike the idea of having many devices communicating wirelessly in our house, arguing that the signals have negative effects on our physical health.
I would like to tell them the EM signals are in fact weaker than the light from…
Chong Lip Phang
- 823
19
votes
6 answers
What does it mean to make a sound twice as loud?
Giancoli Textbook question:
To make a given sound twice as loud, how should a musician change the intensity of the sound?
The given answer is: "Increase the intensity by a factor of 10."
I don't get it, doesn't increasing it by a factor of 10…
SuperMage1
- 301
14
votes
2 answers
Light: Intensity vs Brightness
Is the intensity or brightness of light the same idea? In other words, when we are observing Malus's law, are we looking at the "brightness" of light? If they are not the same quantity, how can we qualitatively see the intensity of light and…
WigbertPowrr
- 409
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13
votes
2 answers
Exact relationship between electric field and intensity
I often see $I(t)\propto |E(t)|^2$. What is the exact form ? Which constants are missing to make this an equality and why are they so often omitted ?
Hans Wurst
- 1,611
12
votes
4 answers
Does light intensity oscillate really fast since it is a wave?
If you shine light on a wall, what will be seen is a "patch" with constant intensity. However, if light is viewed as a wave, then it is oscillations of the electromagnetic field changing from 0 to the amplitude and back really fast. So my question…
Adgorn
- 327
10
votes
3 answers
Why is intensity additive?
In class we came across a problem that is essentially the following:
Suppose a source of sound has an intensity of 70 dB. Suppose 9 additional sources produce the same sound in unison (so 10 identical sources of 70 dB sound). What is the resulting…
M.A.
- 103
9
votes
4 answers
Getting the spectrum of light source at high intensity (for low transmittance measurement)
I am trying to measure the transmittance spectrum through a liquid sample using a visible-NIR spectroscopy (a spectrometer connected to a fiber optics and a collimating lens at the end), with tungsten-halogen light source (through another…
smk
- 93
9
votes
3 answers
Why do we use decibels instead of just using intensity to measure how loud things are?
In my physics book, it says that in the human ear, the sensation of loudness is approximately logarithmic. And that the relative sound intensity is directly proportional to a logarithmic ratio expressed as follows:
$ \beta = 10\log(\frac{I}{I_0})…
Dahen
- 277
7
votes
2 answers
Would different sounds of the same intensity but different frequencies have the same harmful effect on the human ear?
The "safe noise exposure limits" I found on the internet only indicates the intensity of the sound in dB, but not the frequency. Does that mean that e.g. a 120dB sound with different frequencies from 20Hz to 20kHz has the same harmful effects on the…
user629549
- 73
7
votes
1 answer
Net intensity for interference from incoherent sources
Why do we simply add the intensities for interference from two incoherent sources? What's the proof for that? I know that incoherent means that their phase difference changes with time
SM Sheikh
- 95
7
votes
4 answers
Energy conservation in the combination of two coherent beams
I was asked a question today by a student that I couldn't find a satisfactory answer to.
Imagine we have two identical laser beams with average electric field strength $E$. Upon combining these beams (assuming perfectly phased to interfere…
Riley Scott Jacob
- 5,138
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6
votes
1 answer
Relation between intensity of light and amplitude of electric field?
A question in my textbook involve finding the electric field amplitude at a point in space given the intensity of light. It uses the following equation to solve it:
$$I=\frac{1}{2}\epsilon_{0}|E|^2c$$
But where did this equation come from? I am…
Marcus
- 115
5
votes
3 answers
Does the number of photoelectrons depend on the area of the beam for a given beam power?
I don't understand something in the photoelectric effect experiment (which consists in shining light to a metallic material and then measuring the kinetic energy of the ejected electrons, as well as the amount of ejected electrons).
From what I have…
niobium
- 754
5
votes
2 answers
Sound waves adding up
If there is a swarm of bees, why is it louder than a single bee? This question may sound stupid but ... if they are all buzzing at the same frequency with the same loudness and the phases of the sound waves are random, should they not cancel out…
Hyp
- 159
5
votes
2 answers
Inverse Square vs Exponential
I feel a little foolish asking this, but I keep reading sources which say that for an inverse square law relationship, e.g. light intensity vs distance from source, the intensity decays exponentially.
Are inverse square and exponential the same? I…
RC_23
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