有關光速的問題

hales

[quote:6c7ba00fd9="wychan"][quote:6c7ba00fd9="Billy"][quote:6c7ba00fd9="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[/quote]

yes~光線是會受到力場所影響 這就是愛因斯坦..的重力透鏡....
but....這是因為重力場令空間彎曲所至 並不是因為引力場的把光線吸引

以現今所知的物理學現象所能解釋的範圍之內 能量的傳送亦必需要
透過media (相對論中否定的"以太"!?!?) 所以目前已知的理論當中
只能建基於物質不能以超過光速運動 但永遠都會有prediction的......
在prediction中光子在受到極強大的力場所引導的時候是有機會以超過
光速的速度移動...

不過最近聽過一些學說所講 物質.包括光子被黑洞吸入之後不會經過
所謂的蟲洞再透過白洞去到另一個時空...反過來是會被黑洞吸入之後
以另一個方式在黑洞內噴返出黎... :?:

亦有論理講話......光子受到黑洞的強大引力場拉扯之下 只會以臨界速度
圍繞黑洞中心運行....因為受到黑洞的引力場所響影 不能逃離黑洞的引力場..
這都是目前人類還不能統一的理論 邊個先岩就不得而知了... :shock:

如果真係有人証實到愛因斯坦所predict能夠以比光速更快的速度
運動的話......應該係超級大新聞喎...........當速度超過光速的話
就會穿越時空.....

"在你出現之前 我就看到你了....因為你的影象比你更早就到達我面前了......"
時間...是相對的....在你的時空內這一刻 是我的時空內的另一刻...
因為我...和你..是屬於不同時空內的observor... :em18:
(我對相對論的理解超級有限.....可能只算係有一些concept 有o的野可能搞錯左都未定 :mrgreen: )

wychan

[quote:566d81728d="stephenyeong"][quote:566d81728d="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[/quote]

this may be caused by the mass of electron (in term of wave density) is heavier then photon.

wychan

[quote:614763bba5="stephenyeong"][quote:614763bba5="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[/quote]

this may be caused by the mass of electron (in term of wave density) is heavier then photon.

hales

[quote:9f6e40f8e4="wychan"][quote:9f6e40f8e4="stephenyeong"][quote:9f6e40f8e4="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[/quote]

this may be caused by the mass of electron (in term of wave density) is heavier then photon.[/quote]

it always be Ture Photon is "Mass-less"......
但係有o的野好似....搞錯左喎.........
以我讀physical chem所學到既....

電能的傳送 並不因為電子由導線的起點帶著能量走過去終點.....
能量是透過電子傳送但不是以"移動"的方式來傳送.....

電子它受到能量的激發後 會把能量吸收 然後由一個energy level
跳到一個較高的energy level 當它由高energy level下降返去
ground state時 就會把能量釋放到另一粒電子 就這樣把能量傳送出去
它所帶的能量只會同他的頻率有關係 by equation E=hv

stephenyeong

electron also massless

position + electron = photon

電能的傳送 並不因為電子由導線的起點帶著能量走過去終點.....

所以我問signal的速度 不是electron 的速度.

hales

[quote:7c2260f46b="stephenyeong"]electron also massless

position + electron = photon

電能的傳送 並不因為電子由導線的起點帶著能量走過去終點.....

所以我問signal的速度 不是electron 的速度.[/quote]

so....我認為是..一樣的....

Billy

[quote:3b6006bc8a="hales"][quote:3b6006bc8a="stephenyeong"]electron also massless

position + electron = photon

電能的傳送 並不因為電子由導線的起點帶著能量走過去終點.....

所以我問signal的速度 不是electron 的速度.[/quote]

so....我認為是..一樣的....[/quote]

佢係好似wave咁傳送就會有propagation constant.
所以你只可以講話係接近一樣.
但唔可以講話係一樣.
所以點講都係光怏速係快少少o既.

stephenyeong

one more hints
點解光會折射? 折射率又是什麼?

unicorn

所以我問signal的速度 不是electron 的速度.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
oops
your question is REALLY a question to elect engineer
not to physics guys
for a signal in 電線 it depends very much on those cap/inductance operating frequency and also the VOLATAGE
of how a CAT 5 cable can function
即係我地日日overclock PC既topics

however
for a optics fibre
it only depends on the signal wavelength and the modulator demodulator and media etc

that is why 電線 technology bandwidth advancement慢
that is why opto technology bandwidth advancement快

有錯請更正

stephenyeong

大家將個問題想得太遠了.

等我就開估啦
答案是電波在cable快過光在光纖的速度.

光速在vaccum ( c ) 的速度大約 300000000meter per second

光在光纖裏的速度大約有0.7c ~ 210000000m/s
而emf在銅線的速度基本有0.7c - 0.8c (好似coaxial cable可以去到90%).

個terms好似叫Nominal Velocity of Propagation