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Science question that actually IS interesting:





ocalhoun
We all know that light travels much faster than sound. (hopefully)
Here's the question: Why?


My best guess is because of it's higher frequency.
However, if thats true, then does blue light travel faster than red light?
If it does, why dosen't that cause problems with multiplexing fiber lines?
Because of these questions, I am inclined to doubt my theory of why light is faster than sound.
Lennon
1st year physics.
Sound is vibrations in the air. The molecules vibrate in a chain reaction in all directions, and the vibrations hit your ear, which translates the vibrations into signal. There's no sound in space where there's no atmosphere.
Light is radiation. It is pure energy like sound, but needs no intermediate, it is self-propogating and can travel through space. Light travels faster than electricity (electrons are slightly slower due to a small mass).
S3nd K3ys
Sound is a 'mechanical' wave. It requires a medium in which to travel, such as a gas, liquid, or solid.

Light on the other hand is a transverse electromagnetic wave. It does not require a medium in which to propagate.

That is why sound can actually travel faster in some mediums than light can.
SunburnedCactus
And different colours have different wavelengths.

Solved!
TheDrunkenClam
Last I heard, the nature of light isn't completely understood. There's talk of the wave/particle duality. In some instances light acts very wave like. I'm told that light is composed of a magnetic wave and electric potential wave perpendicular to each other. In other instances light acts like a particle. I think the particle nature is what a photon refers to. Either way, light slows down in the presence of denser matter, where as sound travels faster in a denser medium. It is definitely conceivable that sound could travel faster than light.

As to your theory of frequency, the speed of light is a constant for a given medium. Actually, all radiation will travel at the same speed in a given material I believe. So blue light, red light, infrared, x-rays etc. will all travel at 2.99 X 10^8 m/s. As stated before, I think the speed difference has to do with the medium more than anything else.
embrace.guild
What they said makes perfect sense. The only thing i dont agree with is that sound will travel faster than light on some mediums? What is that. No way can sound go faster. Light is pure energy, so it really cant be stopped. I want proof that sound can go faster than light
hac
In air sound is a longitudinal wave i.e it travels by means of compressiona and rarefactions. According to Laplace's theory these compressions and rarefactions are adiabatic processes by which he derived that the speed of sound is approximatelt 330 m/s. I can give you the derivation it you want it.

Anyways that explains the spped of sound. Now about the speed of light. Light is an electromgnetic wave which has properties similar to transverse waves but do not require a medium for propogation. Electromagnetic waves have very high speeds approximately equal to 3*10^8 m/s. That's why light is so fast. In vaccum and air all the wavelenghts of light have almost the same speeds while at the same time when they pass on to a medium of greater optical density they get split up due to change in their velocities. This explains Newton's spectrum experiment. Now if I remember correctly from my class 10 text book. Blue light bends the most. This means it has greater refractive index which in turn is the ratio of speed of light in one medium to that in the other (I know that sounds confusing!). Blue light having greater velocity hs greater refractive index and vice versa. Thus from newtons experiment we can understand that blue light is faster than red light bacuse blue has greater deviation from the mean path:

Lennon
This is a mis-interpretation.
To try and keep it simple for the school-students, a prism splits the white light into all its different colours. The same happens when light hits a film of oil over water.

Even though all the colours travel at the same speed, they have different wavelengths. Small wavelengths bend more when they hit a medium with a different refractive index. Blue bends more than red. Larger wavelengths like red hit a medium and bend less. Infrared radiation has a much lower wavelength, and your eye can't see it. The bending is known as refraction (the rays slow down upon entering specific medium). White light is all the wavelengths in coherence, (in the same direction). When white light hits the surface, the rays bend and the colours separate out by wavelength.
hac
I didn't say that refractive index bends the different colors. As you have said wavelengths for different waves are different. So lets consider the equation:

wave velocity = frequency * lambda

Since frequency is a constant for the all the colors speed would depend directly on their wavelenghts. And by the spectrum experiment we can say which has least and max wavelenght and thus leadingto our answer of wave velocity of diff lights. I'm not the sharpest pencil in the box abt this stuff but I hope I'm rite.
Lennon
no, you nearly had it.

c=f*lamba (lambda is wavelength)

c is constant, given by "hac" above, see my diagram which explains how to keep the speed constant,. If wavelength increases, frequency decreases. For this reason, gamma radiation is very low wavelength, but high enough frequency, and given E=hf, has enough energy to form matter. I've used a similar diagram in the past to explain how in the beginning there was light, then light created matter, like the 1st story in genesis.

you can find out a lot more about c. the speed of c as "hac" said is 3*10^8, and this is the maximum speed of electromagnetic radiation, gravitons, the the field of the strong and weak forces. The only thing that happens when light appears to slow down is described by special relativity, under the force of gravity.
Nyizsa
hac wrote:
Since frequency is a constant for the all the colors...

Actually, frequency is NOT constant, this makes them different colors.
To put my opinion in:
If you see that picture with the prism, you will notice that the higher the frequency, the more the light diffracts. But they spend EXACTLY THE SAME TIME IN THERE! Which means that inside the prism blue light is faster than red, because it runs a longer trajectory in the same time. This also applies to the angles of the diffractions.
bassgs_17
Hooray, Physics! Fiber optic telecommunications is revolutionizing our world, so I feel that is important for everyone to understand how light works. I laugh at the sheer volume of replies to this topic. Ha.
-Aquastrike
a.Bird
embrace.guild wrote:
What they said makes perfect sense. The only thing i dont agree with is that sound will travel faster than light on some mediums? What is that. No way can sound go faster. Light is pure energy, so it really cant be stopped. I want proof that sound can go faster than light


Sound travels through water much faster than light. Actually, much farther. Sound travels even farther through metal.
hac
Point taken. I was under some misconceptions which I resolved with my physics prof today. Thanks for the corrections. I understand perfectly now. Thanks a lot guys.

I still have a doubt concerning Nyisza's explanation. Refarctive indes is the ratio of speed of light in one medium to that in another A we have agreed upon speed of light in diff air is same for all wavelengths. But at the same time refractive index of diff wavelengths in glass prism are diff. So naturally velocity must be different for diff wavelengths in glass medium. Is that correct?
adiutrix
S3nd K3ys wrote:

That is why sound can actually travel faster in some mediums than light can.


Are you sure on that? I think not. Nothing has been proven to travel faster than light AND, if you are travelling at the speed of light (probably impossible) and you shine a beam of light from yourself, that light will travel at the speed of light FROM the speed of light if you get me. Technically it can reach infinite speed but that will never happen.
tidruG
hac wrote:
Thus from newtons experiment we can understand that blue light is faster than red light bacuse blue has greater deviation from the mean path

Your explanation was correct upto this point...
In reality, Refractive Index (mju) is defined as the ration between the speed of light in vacuum (roughly 3 * 10^8 m/s) to the ratio of light in a particular material. Since Violet gets reflected the most, it has the highest refractive index for a given material, which means it would be the slowest in any given material.

And while what Lennon said about speed of light being constant in any medium, we generally consider phase velocity in the formula for mju... Since I am an electronics student, I won'tbe able to explain in great detail about this... most of what I'm telling you comes from my basic education about light and its propagation in hgih school.


As per Einstein's energy-mass relation, anything particle having a mass that travels faster than light will become pure energy. Sound is an energy wave propagated by material particles... the more denser the material though which the wave is propagating, the faster it will go... but if any particle that helps to propagate the wave was to move faster than the speed of light, it would become radiation... so sound cannot travel faster than light.
Nyizsa
What is sound? When particles of a given material resonate, and the effect of the resonation propagates. So, since effect is not material, it doesn't have mass. The speed of this effect is unique for every material sound propagates in.
By the way, it is possible for a particle to move faster than light. But only in a certain material!! Search for the Cherenkov-effect or look at this Wikipedia page: http://en.wikipedia.org/wiki/Cherenkov_effect.
So it is also possible for sound.
So, back to refraction: Yes, I was wrong in my previous post. Actually blue travels slower than red. The thing is that they would spend the same time in the glass if its sides were parallel! Sorry Crying or Very sad
Here's a very good applet for experimenting: http://www.ngsir.netfirms.com/applets/RefractionByPrism/RefractionByPrism.htm
Neo7
Well sound travels in Longitudinal Waves created by motion in air particles that can be illistrated by throwing a rock into an undisturbed lake or puddle.

Light is basicly an electromagnetic radiation wave (same as Gamma Radiation, but at a lower, safer level). These waves are capable of traveling without any form of medium what so ever.
TheDrunkenClam
To muddle things up, a while back some researchers managed to stop light. Here's a copy of an article about it. http://www.news.harvard.edu/gazette/2001/01.24/01-stoplight.html
hac
TheDrunkenClam wrote:
To muddle things up, a while back some researchers managed to stop light. Here's a copy of an article about it. http://www.news.harvard.edu/gazette/2001/01.24/01-stoplight.html


Unbelieveble! I would really love to see how loight looks like then.
paradox
Light is a constant and according to einstin nothing can acheave this velocity. thats what his E=mc^2 means. Now light is both a wave and a partical. For example: as a partical it is able to tavel through a medium such as space which sound could not. And about the blue light travleing faster than red, this is no true. All light travels at a constant. But blue does does have a shoter wavelength. But all light travles at a constant rate. Heres the tricky part. Light can be slowed down. When light travles threw certant mediums it is met with resestance and travels at a slower velocity. I was ever reading a few years ago that they were able to stop light compleatly, which was promissing because it is the first step to building a quantum, a computer that runs on light, not electricty.
root
S3nd K3ys wrote:
Sound is a 'mechanical' wave. It requires a medium in which to travel, such as a gas, liquid, or solid.

Light on the other hand is a transverse electromagnetic wave. It does not require a medium in which to propagate.

That is why sound can actually travel faster in some mediums than light can.


There is no medium in which sound can travel faster than light......
Bengt
Lennon wrote:
1st year physics.
Sound is vibrations in the air. The molecules vibrate in a chain reaction in all directions, and the vibrations hit your ear, which translates the vibrations into signal. There's no sound in space where there's no atmosphere.
Light is radiation. It is pure energy like sound, but needs no intermediate, it is self-propogating and can travel through space. Light travels faster than electricity (electrons are slightly slower due to a small mass).

i was about to say this Very Happy
peterstephens
Quote:
I've used a similar diagram in the past to explain how in the beginning there was light, then light created matter,
Lennon

Would you mind spelling this out for me. How does light create matter? Thanks
Lennon
Light is electomagnetic radiation.

A magnet attracts opposites by emitting a magnetic field
Electricity works by positive electric fields attracting negative electric fields, hence the attraction of electrons which are negative towards protons which are positive.

Each of these fields are invisible but the radiation can be detected. The electric field is detected using a voltmeter and the magnetic field can be detected with a compass. These fields which are invisible emit radiation.
Magnetic Fields cause electrons to move
Moving electrons cause an electric field (potential).
Electric fields also induce another magnetic field
So we have a circuit. Magnetic field moves electrons, which produce an electric fieldn, which produce a magnetic field, which moves electrons, which produce an electric fieldn, which produce a magnetic field, which moves electrons etc...

An electromagnetic radiation is a special field where the magnetic field causes an electric field, which causes a magnetic field, which causes an electric field, which causes a magnetic field etc.
The cycle has a frequency and a speed.
Electromagnetic radiation can have many levels of energy. Gamma radiation is very energy intensive, radio frequency radiation is very low energy.

See the diagram with this link
http://student.dcu.ie/~lennonr2/em_radiation.jpg

Visible light has energy about mid-range. It has enough energy to cause stimulation in the eye. Infra-red has a little less energy, ultraviolet has a little more energy.

Gamma radiation forms matter, electrons and positrons (negative and postive). This is because gamma radiation has lots of energy, and when you convert energy to mass, you need lots of energy (E=mc2).

As the universe expanded, it started as an energy-reactor. Just radiation everywhere. As the universe cooled, gamma radiation began to form matter; electrons and positrons. As the universe cooled further, positrons died out and atomic nuclei began to form. As the universe cooled further, atoms formed like hydrogen and helium. And the rest is history. In the beginning was light, then the stars in the sky, then the earth etc.
our-trip-to-cotlands
Good question, that could stump my science teacher. *waits for tuesday* *asks teacher question* *gets the what the **** look back*
edallica
Lennon wrote:
Light is electomagnetic radiation.

A magnet attracts opposites by emitting a magnetic field
Electricity works by positive electric fields attracting negative electric fields, hence the attraction of electrons which are negative towards protons which are positive.

Each of these fields are invisible but the radiation can be detected. The electric field is detected using a voltmeter and the magnetic field can be detected with a compass. These fields which are invisible emit radiation.
Magnetic Fields cause electrons to move
Moving electrons cause an electric field (potential).
Electric fields also induce another magnetic field
So we have a circuit. Magnetic field moves electrons, which produce an electric fieldn, which produce a magnetic field, which moves electrons, which produce an electric fieldn, which produce a magnetic field, which moves electrons etc...

An electromagnetic radiation is a special field where the magnetic field causes an electric field, which causes a magnetic field, which causes an electric field, which causes a magnetic field etc.
The cycle has a frequency and a speed.
Electromagnetic radiation can have many levels of energy. Gamma radiation is very energy intensive, radio frequency radiation is very low energy.

See the diagram with this link
http://student.dcu.ie/~lennonr2/em_radiation.jpg

Visible light has energy about mid-range. It has enough energy to cause stimulation in the eye. Infra-red has a little less energy, ultraviolet has a little more energy.

Gamma radiation forms matter, electrons and positrons (negative and postive). This is because gamma radiation has lots of energy, and when you convert energy to mass, you need lots of energy (E=mc2).

As the universe expanded, it started as an energy-reactor. Just radiation everywhere. As the universe cooled, gamma radiation began to form matter; electrons and positrons. As the universe cooled further, positrons died out and atomic nuclei began to form. As the universe cooled further, atoms formed like hydrogen and helium. And the rest is history. In the beginning was light, then the stars in the sky, then the earth etc.


will people stop opsting things in this thread that are absolute non-sense? why would you post something that you think is true and not fact? geez.

the resulting of DISPERSION is due to the refractive index being a function of wavelength. i find it amazing that this topic has got so far without the word dispersion being involved at any point. or, that posts as long as my arm rant about (with disgusting diagrams) the bending of blue light with respect to red and not actually explain anything.

if you dont know what you're talking about you should not state in terms of fact. you should offer your opinion but DO NOT give people completely wrong information. i am specifically aiming at Lennon here.

i mean this guy as well...

a.bird wrote:
Sound travels through water much faster than light. Actually, much farther. Sound travels even farther through metal.


that does not mean anything to anyone.
SunburnedCactus
edallica wrote:
Lennon wrote:
Light is electomagnetic radiation.

A magnet attracts opposites by emitting a magnetic field
Electricity works by positive electric fields attracting negative electric fields, hence the attraction of electrons which are negative towards protons which are positive.

Each of these fields are invisible but the radiation can be detected. The electric field is detected using a voltmeter and the magnetic field can be detected with a compass. These fields which are invisible emit radiation.
Magnetic Fields cause electrons to move
Moving electrons cause an electric field (potential).
Electric fields also induce another magnetic field
So we have a circuit. Magnetic field moves electrons, which produce an electric fieldn, which produce a magnetic field, which moves electrons, which produce an electric fieldn, which produce a magnetic field, which moves electrons etc...

An electromagnetic radiation is a special field where the magnetic field causes an electric field, which causes a magnetic field, which causes an electric field, which causes a magnetic field etc.
The cycle has a frequency and a speed.
Electromagnetic radiation can have many levels of energy. Gamma radiation is very energy intensive, radio frequency radiation is very low energy.

See the diagram with this link
http://student.dcu.ie/~lennonr2/em_radiation.jpg

Visible light has energy about mid-range. It has enough energy to cause stimulation in the eye. Infra-red has a little less energy, ultraviolet has a little more energy.

Gamma radiation forms matter, electrons and positrons (negative and postive). This is because gamma radiation has lots of energy, and when you convert energy to mass, you need lots of energy (E=mc2).

As the universe expanded, it started as an energy-reactor. Just radiation everywhere. As the universe cooled, gamma radiation began to form matter; electrons and positrons. As the universe cooled further, positrons died out and atomic nuclei began to form. As the universe cooled further, atoms formed like hydrogen and helium. And the rest is history. In the beginning was light, then the stars in the sky, then the earth etc.


will people stop opsting things in this thread that are absolute non-sense? why would you post something that you think is true and not fact? geez.

the resulting of DISPERSION is due to the refractive index being a function of wavelength. i find it amazing that this topic has got so far without the word dispersion being involved at any point. or, that posts as long as my arm rant about (with disgusting diagrams) the bending of blue light with respect to red and not actually explain anything.

if you dont know what you're talking about you should not state in terms of fact. you should offer your opinion but DO NOT give people completely wrong information. i am specifically aiming at Lennon here.

i mean this guy as well...

a.bird wrote:
Sound travels through water much faster than light. Actually, much farther. Sound travels even farther through metal.


that does not mean anything to anyone.


Actually, I daresay Lennon has posted some the most informative and credible scientific explanations on both this thread and the rest of the forum.

You on the other hand have just posted a brainless rant that is "absolute non-sense", says nothing, and has no evidence to back it up.

geez.
myrevolt
s3nd k3ys had the clearcut non-technical answer. and yeah this is why i got a D in AP Physics Sad
[FuN]goku
your asking a grade 9 about this? Very Happy im no good at science but am very good at math
Lennon
To be precise I answered the fellow frihosters request to explain how light can create matter.

As I've done 4 modules in physics (2 general 1st year, the last two were optical physics), I can not only explain refractive index in terms of multiple layers (inlcuding depolarising and total internal reflection effects), I can also show you how refractive index can also produce fraunhaufer and mie scattering, like in cut diamonds or oil films. Besides the point.
I'm trying to avoid scientific jargon like dispersion to explain to all the 9th graders here etc.

And since refractive index is the same for all wavelenths of light, they all travel at the same speed in any given medium, so this is not a problem for optical fibres. what is very interesting is that blue wavelength transmitters and receivers (transmitting the signal) can have a higher capacity than red wavelength. Hence blue-ray is invented to replace the older red-ray.
Jack_Hammer
Lennon wrote:
1st year physics.
Sound is vibrations in the air. The molecules vibrate in a chain reaction in all directions, and the vibrations hit your ear, which translates the vibrations into signal. There's no sound in space where there's no atmosphere.
Light is radiation. It is pure energy like sound, but needs no intermediate, it is self-propogating and can travel through space. Light travels faster than electricity (electrons are slightly slower due to a small mass).


What he said, pretty much...
Rolling Eyes
SNES350
paradox wrote:
Light is a constant and according to einstin nothing can acheave this velocity. thats what his E=mc^2 means. Now light is both a wave and a partical. For example: as a partical it is able to tavel through a medium such as space which sound could not. And about the blue light travleing faster than red, this is no true. All light travels at a constant. But blue does does have a shoter wavelength. But all light travles at a constant rate. Heres the tricky part. Light can be slowed down. When light travles threw certant mediums it is met with resestance and travels at a slower velocity. I was ever reading a few years ago that they were able to stop light compleatly, which was promissing because it is the first step to building a quantum, a computer that runs on light, not electricty.

For most purposes, light is thought of as a wave, but there are some cases in which light acts more like a particle than a wave (quantam physics =>light as particles, called quanta (quantum singular)).
edallica
SunburnedCactus wrote:
edallica wrote:
Lennon wrote:
Light is electomagnetic radiation.

A magnet attracts opposites by emitting a magnetic field
Electricity works by positive electric fields attracting negative electric fields, hence the attraction of electrons which are negative towards protons which are positive.

Each of these fields are invisible but the radiation can be detected. The electric field is detected using a voltmeter and the magnetic field can be detected with a compass. These fields which are invisible emit radiation.
Magnetic Fields cause electrons to move
Moving electrons cause an electric field (potential).
Electric fields also induce another magnetic field
So we have a circuit. Magnetic field moves electrons, which produce an electric fieldn, which produce a magnetic field, which moves electrons, which produce an electric fieldn, which produce a magnetic field, which moves electrons etc...

An electromagnetic radiation is a special field where the magnetic field causes an electric field, which causes a magnetic field, which causes an electric field, which causes a magnetic field etc.
The cycle has a frequency and a speed.
Electromagnetic radiation can have many levels of energy. Gamma radiation is very energy intensive, radio frequency radiation is very low energy.

See the diagram with this link
http://student.dcu.ie/~lennonr2/em_radiation.jpg

Visible light has energy about mid-range. It has enough energy to cause stimulation in the eye. Infra-red has a little less energy, ultraviolet has a little more energy.

Gamma radiation forms matter, electrons and positrons (negative and postive). This is because gamma radiation has lots of energy, and when you convert energy to mass, you need lots of energy (E=mc2).

As the universe expanded, it started as an energy-reactor. Just radiation everywhere. As the universe cooled, gamma radiation began to form matter; electrons and positrons. As the universe cooled further, positrons died out and atomic nuclei began to form. As the universe cooled further, atoms formed like hydrogen and helium. And the rest is history. In the beginning was light, then the stars in the sky, then the earth etc.


will people stop opsting things in this thread that are absolute non-sense? why would you post something that you think is true and not fact? geez.

the resulting of DISPERSION is due to the refractive index being a function of wavelength. i find it amazing that this topic has got so far without the word dispersion being involved at any point. or, that posts as long as my arm rant about (with disgusting diagrams) the bending of blue light with respect to red and not actually explain anything.

if you dont know what you're talking about you should not state in terms of fact. you should offer your opinion but DO NOT give people completely wrong information. i am specifically aiming at Lennon here.

i mean this guy as well...

a.bird wrote:
Sound travels through water much faster than light. Actually, much farther. Sound travels even farther through metal.


that does not mean anything to anyone.


Actually, I daresay Lennon has posted some the most informative and credible scientific explanations on both this thread and the rest of the forum.

You on the other hand have just posted a brainless rant that is "absolute non-sense", says nothing, and has no evidence to back it up.

geez.


would you like me to go through everything in this thread that is completely and utterly wrong(cause there is sure a lot of it)?

lennon has not supplied any evidence to anything. most of the things he has said have either been way off topic or completely wrong. the only reason i rant is due to people supplying wrong information, which he is constistanly doing.

seriously, refractive index is a function of wavelength.

i really feel sick when people go away believing some rubbish that people who dont know what they are talking about post.
Mgccl
because light is very light
but sound isn't anything
peterstephens
Lennon wrote:
Light is electomagnetic radiation.......(snip)........


Thanks for that. I get what you are saying about positrons and electrons being matter, and they originated as the energy of electromagnetics and so on. I am no expert, but I would say this can be confirmed in studying matter. I am perhaps looking now at what you mean by creation. Would a better word be transformed? The trouble I have is that matter as we know it is not just appearing, and disappearing, nor changing from what is known about the elements, as in the sense of creation is it? Or perhaps it is me who has the wrong idea of creation?
kolinraff
Ive heard people talking about that nothing with a mass can travel the sound of light , otherwise it would open a black hole! (RUMOUR). Light particles dont have a mass thats why they travel that speed. Also sound cannot travel in vacuum. It needs a medium to travel in!
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