Tornado

p + ρgz = constant  [Bernoulli's equation]

p, ρ都是z的function, 但differentiate兩邊against z

dp/dz  + ρg + dρ/dz  gz  = 0
dp/dz   =  – ρg – dρ/dz  gz
這是不正確，沒有physical meaning的，正確的應是:
dp/dz = – ρg

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The moving system of a D’Arsonval galvanometer consists of a coil of wire and a mirror suspended by a fine fiber and capable of rotation about a vertical axis. Random collisions of air molecules with the suspended system produce torques which are not equal and opposite at all instants. The result is that the angular position is continuously fluctuating and the system exhibits an unsteady “zero” (an example of Brownian motion). If the root-mean-square angular displacement of the system is θ_rms = 2 × 10^-4 rad and the torque constant for a fine quartz fiber is K = 1 × 10^-13 N m /rad , find the temperature of the air.
(From 3000 solved problems in Physics)

solution:
=> energy modes for these system: rotational kinetic and torsional potential energy
=> equipartition theorem applies to both types of disordered energy
=> 1/2 K θ_rms ² =1/2 k T
=>  T = 290K

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用meter前要:

• set zero / 計offset
• 較intensity / attenuation , unit
• distance, polarization, background, 有無focus好, d野係咩parallel, 做左calibration未

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HP 54602B 150Mhz Oscilliscope – HP Tetris
Computers, Hardware
1. Turn on the o-scope.
2. When running, press “PRINT/UTILITY”
3. Simultaneously hit the 2nd and 3rd soft keys (and hold for a half a second)
4. The game should pop up!

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http://en.wikipedia.org/wiki/Function_generator

Signals which last for a very short period of time are referred to as “ TRANSIENT Signals”.

http://en.wikipedia.org/wiki/Coupling_(electronics)

In electronics and telecommunication, coupling is the desirable or undesirable transfer of energy from one medium, such as a metallic wire or an optical fiber, to another medium, including fortuitous transfer.

Also the transfer of power from one circuit segment to another. E.g., an alternating voltage may be transferred to a segment at a different direct voltage by use of a capacitor or transformer; power may be efficiently transferred to a segment with different impedance by use of a transformer.

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larger degree of freedom => larger energy => entropy (in positive temperature) is larger
越自由越凌亂
[物理看人生 = ="]

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點解mixture of liquid的boiling point低d
=>http://www.jyu.fi/kastdk/olympiads/1998/ps.zip （睇第一題）

neutron [matter-wave] interference, using gravity
=>http://www.jyu.fi/kastdk/olympiads/2006/IPhO-37_Th1_final.pdf

What Does Negative Temperature Mean?
-300K 「熱過」 273K

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物理一題（F.3程度的熱力學, F.4 Chem的知識）：
The amount of heat required to convert 1g of ice into vapour is approximately 3000J. Estimate the energy required to separate one molecule from a single neighbour, assuming that, in ice, each H2O molecule has four nearest neighbours. [Relative molecular mass of water=18, Avogadro constant=6.02 x 10 ²³ mol ^-1]

4.5 x 10^-20J
特別之處解法有點數學技巧。
Graph theory: The sum of the vertex degrees in any undirected graph is twice the number of edges.
簡單來講，就是如果在一個宴會上，握手次數共為m次，且每兩個人之間最多握一次手；則 甲握手次數+乙握手次數+… =2m
From “Cambridge Problems in Physics and Advice on Solutions”