有關光速的問題

stephenyeong

睇得和記寬頻個廣告多

有幾多人知 光在光纖行得快 還是signal在cat5 cable 行得快?

答案明晚公佈.

grassman

好明顯啦！

wychan

呢個要視乎導體(media)對訊號(signal: 即光或電子流動)所產生的抗阻(resistance)而形成的衰減(attunation)有機大而決定. 所以要睇下用什麼光纖及cat5線。


解釋如下
Question:  DOES THE ELECTRON TRAVEL AT THE SPEED OF LIGHT?
------------------------------------------------
Answer:  No.  If you calculate the instantaneous speed of electron
using the theoretical models it comes out to be the velocity
of light.  However we cannot measure instantaneous speeds but only
speed averaged over some time scale by measuring position at two
instants of time.  When we do this the speed is always less than
the velocity of light.  Theoretical models also predict average
velocity less than speed of light.
The above discussion only applies to speed of light
in vacuum.  Electrons can  and do travel at
speeds faster than
speed of light in some media.
Jasjeet


SOURCE FROM http://www.newton.dep.anl.gov/askasci/phy99/phy99372.htm

stephenyeong

[quote:01407334a3="wychan"]呢個要視乎導體(media)對訊號(signal: 即光或電子流動)所產生的抗阻(resistance)而形成的衰減(attunation)有機大而決定. 所以要睇下用什麼光纖及cat5線。


解釋如下
Question:  DOES THE ELECTRON TRAVEL AT THE SPEED OF LIGHT?
------------------------------------------------
Answer:  No.  If you calculate the instantaneous speed of electron
using the theoretical models it comes out to be the velocity
of light.  However we cannot measure instantaneous speeds but only
speed averaged over some time scale by measuring position at two
instants of time.  When we do this the speed is always less than
the velocity of light.  Theoretical models also predict average
velocity less than speed of light.
The above discussion only applies to speed of light
in vacuum.  Electrons can  and do travel at
speeds faster than
speed of light in some media.
Jasjeet


SOURCE FROM http://www.newton.dep.anl.gov/askasci/phy99/phy99372.htm[/quote]

Speed of electron ??
drift velocity of electron

Billy

所有物質o既移動都唔可以快個光速o既.
但如果果樣唔係物質而只係能量o既轉移呢.
就有可能快過光速喇.
但cat5我都覺得唔可能快過光速.

hales

光速同電流脈衝既移動速度都是一樣的....
我覺得應該速度是一樣的....導線的電阻會令到
電流脈衝所帶的能量減弱 但不會影響行進速度.....

Billy

[quote:0612209ceb="hales"]光速同電流脈衝既移動速度都是一樣的....
我覺得應該速度是一樣的....導線的電阻會令到
電流脈衝所帶的能量減弱 但不會影響行進速度.....[/quote]

係EM WAVE EQUATION 入面.
有propagation constant 同 attentuation constant.
你講果個係attentuation constant.
而propagation constant 同 MEDIA o既 dielectric 的確係有關係o既.
註: 因為現在digital speed 行得好快好多時一般digital signal都會用EM WAVE概念去諗.

wychan

[quote:d8d805c634="Billy"][quote:d8d805c634="hales"]光速同電流脈衝既移動速度都是一樣的....
我覺得應該速度是一樣的....導線的電阻會令到
電流脈衝所帶的能量減弱 但不會影響行進速度.....[/quote]

係EM WAVE EQUATION 入面.
有propagation constant 同 attentuation constant.
你講果個係attentuation constant.
而propagation constant 同 MEDIA o既 dielectric 的確係有關係o既.
註: 因為現在digital speed 行得好快好多時一般digital signal都會用EM WAVE概念去諗.[/quote]

Agree.

其實光都是以粒子形式在媒體上運動 而單位為photon(按弦理論 photo是能量組以弦的方式形成). 運動形或是以wave的形式的能量傳送. 因此光的速度亦會受到媒體的影響. 同時光亦不是一定以直線運行
有實驗証明光會授引力影響而轉灣...

同時 有科學家(好似係霍金)証明了愛因斯坦說光不一定是最快的. 我查下再同大家講

hales

[quote:98e35f6f18="wychan"]Electrons can  and do travel at
speeds faster than
speed of light in some media.
Jasjeet

[/quote]

Sure...? :shock:
C 已經係目前物理學上所定義的最高速度了..
廣義相對論亦必需要幕基於任何物質傳送均不能超過光速..
而在相對論中predict了假如物質以超過光速移動的話 就會........  
在事情發生之前你已經看到事情的結果.... :dead:

stephenyeong

[quote:fb8461090a="wychan"]Electrons can  and do travel at
speeds faster than
speed of light in some media.
Jasjeet

[/quote]

electron travel speed in wire is very slow although free electron can travel at speed of 50% C. Drift velocity of electron is slower then 1m/s.

speed of light / em wave is the maximum speed in specified medium / environment.

Speed of light in vaccum is around 300000000 m/s