2014.11 Mid-term Exam

1. Why is steel tougher than iron ?

2. What is the major weakness of cement as a construction material ?

3. Sewage water treatment can have primary and advanced treatments, what are the the things to be treated respectively.

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

5. What is Brownian Motion ? What has this to do with precipitation of dust in water ?

(5.1) Brownian motion is a random and non-stop motion of small particles (pollen or burned coal dust) in liquid.

(5.2) Based on the Principle of Equal Partition of Energy, each degree of freedom has same kinetic energy (1/2 mass times velocity squire ), so if particle is light, then the speed of random scatting is large and the particle will move much longer distance in all directions and cancel its downward movement by gravitation. However, if particle is heavy, the gravitational force drag it down longer then it is scattered away to other directions, and therefore the net effect being the particle been pull down gradually toward the bottom of liquid. In short, Brownian motion is the reason why very tiny particles in water do not precipitate.

6. In which way phosphorus-free washing powder is better than a non phosphorus-free one ?

7. Why large-size air conditioners and electric baking ovens use 220V power instead of 110V ?

8. At absolute zero temperature, what is happening at microscopic level ?

9. Explain "resonance", and give two examples.

10. Why inverter air-conditioners are more efficient (energy saving) than traditional fix frequency ones ?