| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
31 Mar 2005 11:46:35 AM |
| Object: |
Light EM Waves and Water |
I'm sure this is a simple question but I can't get a simple answer. If
high frequency waves can't penetrate water for more than a few
millimeters. Light is a high frequency wave (much more than 1MHz).
Why can I see light over 150 feet down?
Thanks in advance
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| User: "Homer" |
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| Title: Re: Light EM Waves and Water |
31 Mar 2005 12:01:52 PM |
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<bmin61982@gmail.com> wrote in message
news:1112291195.404077.261550@z14g2000cwz.googlegroups.com...
I'm sure this is a simple question but I can't get a simple answer. If
high frequency waves can't penetrate water for more than a few
millimeters. Light is a high frequency wave (much more than 1MHz).
Why can I see light over 150 feet down?
Thanks in advance
You general statement is wrong.
google it, water has changing "transparency" over wide frequency.
Sea water has some special optical zones that are very clear, and laser/sub
communications are possible.
Some bands of RF work within distances.
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| User: "Uncle Al" |
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| Title: Re: Light EM Waves and Water |
31 Mar 2005 12:15:17 PM |
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wrote:
I'm sure this is a simple question but I can't get a simple answer. If
high frequency waves can't penetrate water for more than a few
millimeters. Light is a high frequency wave (much more than 1MHz).
Why can I see light over 150 feet down?
Because water is transparent - though not to deep red. Absorption
requires a coupling to dissipate the energy. You walk in, you walk
out of successive reaction channels as frequency increases.
Calculate the skin depth of copper wire at 10^5 Hz
d = sqrt(2/wus)
where w = omega = (2pi)(10^5)
u = mu = copper magnetic permeability = (4pi)[10^(-7)]
s = sigma = copper conductivity = 5.8x10^7 mho/m.
This gives d = 0.21 mm. Rule of thumb is to use five times the skin
depth, so a 1.05 mm wire should work.
Applied Electromagnetism, Second Edition, Liang Chi Shen and Jin Au
Kong, PWS Publishers, 1987, p. 54, 57.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "PD" |
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| Title: Re: Light EM Waves and Water |
31 Mar 2005 12:50:55 PM |
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wrote:
I'm sure this is a simple question but I can't get a simple answer.
If
high frequency waves can't penetrate water for more than a few
millimeters. Light is a high frequency wave (much more than 1MHz).
Why can I see light over 150 feet down?
Thanks in advance
Obviously there is a difference of opinion on the definition of high
frequency here. How high is high?
PD
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| User: "bz" |
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| Title: Re: Light EM Waves and Water |
31 Mar 2005 02:43:11 PM |
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"PD" <pdraper@yahoo.com> wrote in news:1112295054.930246.59790
@g14g2000cwa.googlegroups.com:
bmin61982@gmail.com wrote:
I'm sure this is a simple question but I can't get a simple answer.
If
high frequency waves can't penetrate water for more than a few
millimeters. Light is a high frequency wave (much more than 1MHz).
Why can I see light over 150 feet down?
Thanks in advance
Obviously there is a difference of opinion on the definition of high
frequency here. How high is high?
HF is usually 3 MHz to 30 MHz.
--
bz
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+sp@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
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| User: "" |
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| Title: Re: Light EM Waves and Water |
31 Mar 2005 09:31:18 PM |
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Whats the furthest star in the sky you can see with the naked eye?
Depends on how bright the star is.
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