中二科學問題一問

條wire熱唔熱其實睇幾個factor　(current, electical resistivity, length or wire and the cross sectional area）
我逐個解釋比你聽啦
First，for other factor remain unchanged
current 愈大，電線愈熱, why?
Ans:
電流通過，電子會由電線的一端去另一端，係個過程裏面，電子會撞落ｄ唔識動的atom個度，ｄ撞擊就係導致條電線發熱ｄ原因喇，所以，當電流愈大，電子帶的電能愈大，撞擊所傳送的能量也大左，電線相對發熱得大左．
(resistance阻力即，電子通過電線的比atom 阻著的阻力喇/撞擊的次數)

Then
For the cross sectional area and other factor remain unchanged
用個出門口的比喻話教你
一個人出門口，就好似一粒電子走穿過一ｄ唔識動的atoms中間
so, 門口愈大，人通過就愈易，即cross sectional area愈大，電子同atoms的撞擊機會愈少
hence, 根據之前的解釋，電線相對發熱得小左

Then
For the length of the wire and other factor remain unchanged
如果一個人係賽道度跨欄，賽道逾長，會撞倒的機會愈大，即電線愈長，atoms的撞擊機會就愈大喇，根據之前的解釋，電線相對發熱得大左

Then about the electical resistivity,
佢個大少個係depend on唔同的material
electical resistivity愈大，resistance 愈大, then 撞擊次數多左，相對熱ｄ喇

Hence for your question
All wire is in the same current
the longer the wire ther greater the reistance
the larger the cross sectional area, the larger the resistance
and the electrical resitivity of iron is 1.0 × 10-7 Ωm
the the electrical resitivity of copper is 1.72 × 10-8 Ωm
that mean the electrical resitivity of iron is larger than that of copper

Hence, the short, thin iron is the ans

Add oil add oil

其實，呢條問題係關於電阻（resistance）

resistance 愈大，條wire愈熱

∵ iron’s resistance is greater than that of copper
The longer the wire, the greater is the resistance
The thinner the wire, the greater is the resistance　（不過唔知你有無學過）

所以 (c) 的答案中, resistance最大, 因此the hottest ~

hope that can solve your problem＝）

As the iron got a lower conductivity than copper, but a slightly higher heat capacity
so the iron can be hotter than the copper,
then as the thin iron wire can transform the electrcity to heat faster than the thick one

越ｌｏｎｇ同越thin既電阻會越大，

2006-12-23 20:36:52 補充：
你是個英文中學跌渣學生嗎?