The way science works : 2016-1 Final Exam

( Answer strictly five questions only, 20 points for each question The sixth answer will be ignored.)

[This page provide hint just key concepts and structure, they should not be regarded as full answers.]


1. High frequency sound could not be produced by large cone-size loudspeaker, explain why.

Large cone-size disc is heavy and its motion can not catch up high-frequency driving force, therefore motionless and produce no figh-frequency sound.

2. What is the general principle of an amplifier?

Any device where large energy flow or signal flow is controlled by small ones could be used as an amplifier.


3. Spectral colour and non-spectral colour, give two examples for each.

Examples of spectral colour : red, orange, yellow, green, blue, indigo, violet (any colours in rainbow). Non-spectral colour : brown, purple (any colour not in rainbow).


4. What is the definition of ˇ§forming an imageˇ¨?

Lights from any (neighbouring) two points from object must arrive as separate (neighbouring) points on screen or receiver, then an image can be formed.

5. What are the differences between pin-hole and lensed camera.

pin-hole has no lens, poor picture quality, no enough light, objects at any distance can form image inside pin-hole camera.

lens camera has good picture quality, allow lots of light, only objects on the right (focus) distance is clear.

6. What is total reflection? When will that happen? Give two examples.

When light come from large density medium to small density medium, angle measured from the normal of surface will be increased (bent) further. There exist a critical incoming angle so that such outgoing angle is larger than 90 degree, which mean light will never escape from the surface, it is called total reflection.

More sparkling from diamond then other gem stones and the principle of optical communication (glass) fiber not loosing energy for long traveling distance are two examples of total reflection.


7. What is the advantage of using numbers system (i.e., using numeric letters and digits) ?

(1) Any large quantities can be represented as small numbers of (numerical) symbols.

(2) To perform arithmetic operation (such as add , subtract, multiply and divide) only rules for one digit is required. Higher digit just repeat using the same rule.

8. With some circuits to monitor electrical current and show number, a digital thermometer requires only a single piece of semiconductor has sensor of temperature, why?

Semiconductor has small energy gap, so electrons at filled lower energy states can jump to higher empty states and become mobile. When surrounding temperature is higher, there are more free (conducting) electrons. The size of current can then be used as an indication of temperature.


9. The effect of ˇ§resonanceˇ¨ has appeared twice in our course, what units are those?

Microwave oven and radio signal tuning.

10. Radio stations can be selected set to one at each time by adjust the tuner on radio player, what is the principle behind this?

Inside a radio, antenna is connected to a LC circuit, LC circuit is an electrical version of swing and has nature frequency for oscillating currents, i.e. only matching frequency current can exist in the circuit. The resonance frequency of LC circuit is controlled by tunable capacity. User therefore change the filtered signal and choose from different stations.


11. Which one is correct? Exposed to stronger (intense) light, (1) more (photo) electrons escape from semiconductor or metallic surfaces, (2) the escaped electrons have higher energy. Who explained this effect?

"(1)" is correct. Einstein explain this effect.


12. Why is it possible to store so much information onto a DVD disc?

Digital information (as 0 and 1) bits are stored as extremely down-shrink reflective and non-reflective spots on the surface on DVD. When needing to read from DVD, laser beam provide light to be focused into an extremely tiny spot size just small enough to cover bit spots recorded on the DVD earlier. Shining on rotating DVD, the strong and weak reflected light intensity thus give bit 1 and 0.

(It is acceptable if students answer this question by giving the detail procedure of how to make press-produced DVD or burning DVD write-once or DVD re-writable, but he/she must also describe the use of focused laser beam into tiny spot to read bits out from a DVD.)