The Way Sceince Works : 103-2 Mid-term Exam

（一）鋼為什麼比鐵堅韌？

1. Why is steel tougher than pure iron ?

鋼是鐵之中再摻入約百分之五的碳，原子體積較小的碳能卡在鐵原子排列的空隙中，使鐵原子的滑動不易。如此降低鐵的延展性並提高其硬度。

small amount of carbon fit in the gaps between iron atoms, making iron atoms not easy to slide and become not very deformable, and hence harder (toupher).

 

（二）鋼筋與混凝土組合在一起比單獨使用有什麼好處？

2. What is the advantage of mix steel bar and concrete ?

混凝土極耐壓不耐拉，與鋼筋合併使用可增加其耐拉性，如此同時具備耐壓及耐拉的特性。

 

（）明礬（硫酸鋁）加入水中為何能把雜質沈澱掉？

3. Why adding alum (Aliminium Sulfate) precipitates the dusts in water ?

明礬加入水中會產生絮狀物，有捕捉（因布朗運動效應）飄浮於水中之雜質及微生物的作用，一旦凝集之顆粒變大，便不能再作布朗運動而沈澱，如此可使水質清澈。

Floc will form when alum mixed with water, these floc will capture dusts in water to form larger particles. (based on equai-prtition of energy,) making them no longer possible to stay in whter through ramdon Brownian motion, and have to be pull down my gravitaional force and to precipitate instead.

（四）一般污水的處理，主要是要去除污水中的什麼成份？為什麼要這麼做？

4. What is the thing to remove when treating swage water (domestic waste water) ? why ?

要除去水質中剩餘的養份。因為帶有養份的水流入河叫中會造成細菌大量消耗水中氧氣使其他生物之法生存而破壞河川生態。

To remove the nutrition left in the water, otherwise the oxygen in river will be exhausted by bateria consuming the excess nutrition, making all other creatures impossible to live.

（五六）在集水區養殖禽畜有什麼負面影響？

排放養殖廢水中有沼氣（甲烷），遇消毒用的氯會形成致癌物三氯甲烷。

5. Why is it not a good idea to raise livestock and poultry in the water collection area of a dam?

Organic waste can produce methane gas (CH4), which will form CHCl3 (tri chrolo methane), a cancer causing substance, when mixed with chroline that is always added into waterfor killing germs.

6. Explain what is resonance and give one example.

When the frequency external driving force is equal to the natural frquency of a oscillating / vibrating object, the oscilation will be enhanced.

Example (1) when play swing, reqular rhythm is necessary to keep swing going. (2) Soldiers must not march in the same foot steps when passing suspendtion bridge, otherwise the bridge may shake too much.

 

7. When temperature raise, what happen in the microscopic world ?

Atoms or molecules move faster.

（八）水庫不用來發電，反倒是耗電地把水從下游抽到水庫內，是什麼目的？

8. Why sometimes electrical energy is spent to pump water back to resorvior instead of doing opposite to generate power ?

利用離峰時多餘的電力，將水抽回水庫，以供尖峰時再發電用。

Although there will always be energy loss during this procedure, the extra power can fulfil the extra demand of peak hours. It is still beneficial to use the excess amount energy in off-peak hours to pmp water back to dam (or high position resorvior).

（九）為什麼除溼機可以除溼？

9. How dehumidifiers work ?

因為溫暖的空氣比寒冷的空氣更容易攜帶水份。除溼機的內部與冷凍機類似，都有壓縮機、冷媒管、散熱片及膨漲閥。除溼機利用冷媒管冷的部分把空氣冷卻並讓水滴析出，再讓冷空氣吹過冷媒管熱的部分來還原空氣的溫度，如此釋放回室內的空氣其溼度己經降低。

Warm air carry more water than cold air. The componet of a dehumidifer is similar to refrigerator (having compresser, refrigerant, radiator and expansion volve). Air pass through the cold part of tube and causing consendation of moist to drops, thus seperate whter from air, then cod air be reheated back to normal termperature by blowing theorugh the hot part of tube. This has the overall the effect of dehumidification.

（十）為什麼變頻的冷氣可以省電？

10. Why inverter (frequency varying) air conditioner help save electricity bill ?

機械運作總有阻力、因摩擦而耗能本無可避免，但運作速度越快，則但阻力大、耗能越多。想像在游泳池玩水時來個水中跑步，比起水中散步辛苦得多。

不變頻的冷氣，一開啟就要快速用力運作，以便在合理的時間內把房間降溫下來（房間越大，冷氣要越大台，所謂的坪數與噸數的對應值）。等到房間冷了，控溫器 便關掉冷氣，待一段時問室內回溫不夠冷了，再開壓縮機。一開又是快速大耗能運作。變頻的冷氣機，在維持冷房的階段，以低速運行，即足以達成小幅降溫的任 務，又能夠省電。

For fluid, resstance force is proportional to (operating) speed. therefore fast operting machine caused more energy.

The capacity of an air conditioner is designed to be able to quickly bring the temperature down to confortable level reasonably soon, and therefore has to operate on full high speed. However, to maintain that temperature requires switchng on and off all the time. This is very inefficient compare to a slow operating alternative. The invertaer (frequency-varying) model save energy by operating at much lower speed when maintaining the already cooled down termperature in stead of high spped operation but switching on and off all the time.