Laplace's rule of succession - A simple proof

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Why do Indonesians prefer to have a vacation to Singapore, where the daily price is more expensive than Australia?

 Why do Indonesians prefer to have a vacation to Singapore, where the daily price is more expensive than Australia?

1. Airfare cost to Singapore is cheaper than to Australia. Flight to Singapore can cost as low as IDR 800,000 roundtrip (About USD 75)
2. It only takes 1 hour flight to reach Singapore while flight from Jakarta to Sydney takes 6 hours
3. Indonesians don't need visa to visit Singapore, while it cost $100 to have Australia's tourist visa
4. Singapore is small so that tourist can explore it in 1 till 3 days. This can be an efficient option for Indonesians since leave days in Indonesia is really short
5. Public transportation in Singapore is well connected and quite affordable, making it easier to be explore comparing to big cities in OZ like Melbourne, Sydney, and Perth
6. Singapore has great culinary scene with great variety of halal foods, which suitable with Muslim travelers from Indonesia
7. Few Indonesians have relatives in Singapore and many upper class Indonesians have apartment in Singapore
8. Malay language are still used in Singapore, making Indonesians that don't understand English more comfortable when exploring Singapore
9. Singapore climate is same as Indonesia, so that Indonesian tourists don't need special clothes to be prepared
10. Sometimes gadgets/electronic appliances prices in Singapore cheaper than in Indonesia. The specification often more advance. Therefore many Indonesians go there to buy that stuff

F = ma & Ohm's law CONFLICT

 

By Rushi Shroff

ohm's law

Now lets try to really understand Ohm's law, which says that the current in a wire is proportional to the voltage. This law isn't really a law at all, not like the force law of gravity or the law of conservation of energy or momentum. In fact it is really rather astonishing that it should be true at all. Why? The voltage produces an electric field in the wire, which produces a force on the electrons. Now this force produces an acceleration (remember Newton: F=MA) not a velocity, thus we would expect the current to grow larger and larger, as the electrons continue to accelerate, moving ever faster. Instead Ohm's law is saying that this constant electric field is producing a constant current, hence constant velocity. Something funny is going on here. To understand this we need to take a closer look at the goings on in the wire. Remember I said that the electrons are like a gas, filling the wire. Well, these electrons are constantly bumping into things, and bouncing off of them. Think of it as follows: Imagine you are in a Ferrari, and you can go from 0 to 100 in 6 seconds. However, you happen to be on a road where there is a stop sign every three seconds. How fast, on the average do you travel? In three seconds, you've accelerated from 0 to 50. Your average speed during those three seconds was 25MPH. Then you had to slam on the brakes, screech to a halt, and start all over again. Thus even though your Ferrari can do 100 in 6 seconds, your average speed is only 25MPH. Hell, you're not even breaking the speed limit (at least on average.) 

In the general case, we need to relate 
the distance you cover, say L, 
to your acceleration, A, 
and the amount of time, T you are moving. 
At the end of time T, 
your velocity V = A * T. 
The distance you've covered is your average velocity over that time, 
which is V/2, times the time T, 
so L = V/2 * T = 1/2 * A * T * T. 
Thus if we solve for T we get that
 T = Square Root (2 * L / A). 
Finally this means that the current, 
with is the average velocity of the electrons is 1/2 * A * T =  √(L * A / 2). 
Take a breath for a moment and let's see what we've discovered. 
The current is proportional to some constant, 
namely Square Root (L/2) times Square Root(A). 
And A, the acceleration, is proportional to the electric field, which is proportional to the voltage. 
Oops. We must have made a mistake somewhere, because that is not Ohm's law. Ohm's law says the current is proportional to the voltage, not the square root of the voltage. 
What's wrong? Well in a gas, each molecule is constantly moving, because of the thermal energy of the gas. Furthermore, the velocity due to this thermal energy is very large compared to the drift velocity we calculated above. 
In fact it is about 10^9 mm/sec or almost 10 orders of magnitude (10^10) times bigger. 
Thus their motion is totally random, and very fast. 
Therefore the time between collisions is L / thermal velocity, not L / drift velocity. 
The fact that this is 10 orders of magnitude greater than the drift velocity means the drift velocity contributes almost nothing to the time.
 Thus the average velocity between collisions is 1/2 A * T where T does not depend on A at all. Thus the current is proportional to A which is proportional to the voltage, and voila, we have Ohm's law. 
n fact we can squeeze even more information out of this observation. The amount of current flowing down a section of wire is:

current density (I) = 
The number of atoms per unit volume (N) 

times 
the number of free electrons per atom (f) 
times
the charge per electron (q)

 times
the average velocity of the electron (1/2 A * T)

thus: I = 1/2 * N * f * q * A * T
now acceleration A = Force / mass of electron (m) = E / m
and time T = distance between collision L / thermal Velocity V
so I = (N * f * L * q^2 / 2 m V) * E

What have we here? Well, we can see that the stuff in the parentheses, which are all things that depend on the material the wire is made of, is a first order formula for the conductivity. Conductivity is the inverse of resistance, so if we stick all that stuff on the other side of the equation we get:

E (voltage) = (2 m V / N * f * L * q^2) I .... Ohm's law
Which correctly predicts that the resistance should increase as the thermal velocity of the electrons gets larger, or in other words, resistance goes up with temperature, a well know fact.

Now the resistance of a metal like copper is essentially zero, but the resistance of the bulb is substantial. Thus there are a lot more collisions taking place in the filament than in the wire, and guess what, the filament gets hot. The electrical force is being converted into heat, and eventually light by the resistance of the filament, in other words, the flashlight produces light.

旅遊及款待科 2021 DSE 貼題

 又到估題時間，今次疫情對整個旅遊款待行業影響極大，長題涉及行業在此環境下如何打開局面，如何善用旅遊氣泡，如何推廣本地旅遊內需；在疾情結束後如何吸引顧客，如何向顧客推廣使香港成為對方疫後出遊的首選？

今屆貼：

1.

Staycation - hotel operation., 如何保障人客員工健康防止感染。例如無接觸感應，環境消毒機械人。

2.

疫下很多時要避免面對面接觸，customer relations 怎去維持，

RATER  model.

3.

本地遊：發展大嶼山的旅遊優勢，遠足，野營，單車之旅，水上活動...

例如水口泥灘生態遊，鳳凰山觀日出，大澳鹽田等。路線設計，硬件需求。

4.

Disneyland- Theme park-type of theme & characteristic.

5. Doxy index of irritation.

Example of atom excitation

The left picture is a green amber bracelet under normal fluorescent light.

The one on the right is the same piece under "white" LED light.

 Amber is natural resin which is unsaturate-hydrocarbon.

When the the photon energy is high enough the hydrogen atom's electron will be raised from the ground state into higher level. When the electron drop back to ground state the absorbed energy is released in the form of light. 

Internal resistance of power source

 

Differentiation max/min example 3

  看完下面6 parts視頻你已可掌握DSE的Differentiation.

視頻教學：

Differentiation 入門 part 1   part 1 to part 6

如AP cost 是 4700/km