幾條唔洗計既問題(送分)

第一題，如果你有學電線既電阻關係，會易好多(電阻與橫面面積成反比,與長度成正比)。導熱既原理係同佢一樣。導熱與橫面面積成反比,與長度成正比

所以係c，不是d因為鐵比玻璃導熱，常識。


水未過100度唔會變氣體，但佢既密度有少許增加，但可以當作冇變。
熱阻同電阻既原理一樣，所以你應該明吧

1. Heat coonduction is attributed by free electrons (this is the reason why metals, which have plenty of free electrons, are good conductors when compared with non-metals, which have only few free electrons). The heat energy is transmitted from one end of the bar to the other end through vibrations of these electrons.

A larger cross-sectional area enables more number of electrons to transmit their thermal vibrationsto the next layer of electrons at the same time (such as a larger door enables more persons to enter a room at the same time), thus lead to more rapid transfer of heat energy.

2. Most substances expand on heating and contract on cooling (冷縮熱漲). Since the mass of a substance would not change on heating, any expansion leads to an increase in volume, this causes a decrease of density ( density = mass/volume).
But be aware that between 0'C and 4'C, water has a peculiar behaviour in which it expands on cooling and contracts on heating. Thus the density of water increases, instead of decreases, when it is heated from 0'C to 4'C.

1,點解係c?

因為.較粗的鐵棒 切面面積較大.熱阻亦比較細.而且佢係鐵,咁就同導電一樣,切面面積大,傳熱/導電能力都比較良好.

2,加熱,係將能量傳送去物質度.姐係增加該物質既能量,咁就令到份子與份子之間有足夠既能量令到互相既距離加大.從而,減低密度.