Tornado

 

http://www.hkedcity.net/iworld/vote/index.phtml?iworld_id=38 物理廊問題集

http://clem.mscd.edu/~talmanl/MTH1410S07/IdentifyingDerivatives.html
Suitable for F.5

Yahoo知識+

Q: 0的0次方=?

A:
這要視乎情況。例如在數學分析（即是討論lim,微積分等的數學分枝），零的零次方是「Indeterminate form」，要看你計的是甚麼function。而大部分的情況，0^0都可取值為1

但在組合數學，0^0是1。例如根據binomial theorem（不知你的數學程度，這個theorem在中四附加數學有教）
(x+y)^n = sum(k=0 to n) C(n,k) x^k y^(n-k)

設a不等於0， 1=(a+0)^0 = 0!/0! a^0 0^0
因為0!=1， a^0 = 1 ，如果0^0不等於1，這條式便會有錯。

（不知「!」點解可以參考http://zh.wikipedia.org/wiki/%E9%9A%8E%E4%B9%98）

有關0^0的歷史可以看：
http://www.faqs.org/faqs/sci-math-faq/specialnumbers/0to0/
參考資料:

http://en.wikipedia.org/wiki/Empty_product#0_raised_to_the_0th_power

Phy atm question

1 atm=1×10^5 Pa/ 1×10^5 Nm^-2
即一個1m^2的平面受100000N(約10000kg)的壓力
人為何可以抵受？

A:
首先你要明白，壓強和力是不同的。
我聽過的比喻，是：你覺得以下那種情況較痛：
一個很瘦的女士穿高跟鞋用鞋跟踏你
一個比較胖的人穿皮鞋踏你
答案是前者，雖然前者的力較少，但後者受力面積大得多，壓強也較少。

是用針刺你，用拳頭按着你（不是打過來），比較痛？答案是前者，都是同一原理：前者受力面積少，壓強較大。

1 atm這個大氣壓強，相對比針刺，少得多。
不過，我想最重要的原因是：多年在陸上生活，人類的身體已經習慣了，所以沒有不適。

實用的物理書

《牛頓物理駕訓班》
http://www.bookzone.com.tw/event/ws080/index.asp
http://www.books.com.tw/exep/prod/booksfile.php?item=0010315230

《搞笑學物理》
http://www.books.com.tw/exep/prod/booksfile.php?item=0010286820
這本書真是非常有趣，連精子運動的原理也有！ =_=”

要讀明以上兩本書，對Newton’s laws（中四physics課程）要有認識。雖然第一本的書開頭會略略提及，但我推薦你讀《觀念物理1》。其實《觀念物理》這套書雖然是教科書性質，但 它盡量都會講出它和生活息息相關的一面。就算你在教科書讀過，讀《觀念物理》（整套）都應該會有得?，是非常好的參考書。

觀念物理 I
http://www.books.com.tw/exep/prod/booksfile.php?item=0010158613

以上的書公共圖書館都有得借。
你可以上網查下邊個館有：
http://libcat.hkpl.gov.hk/webpac_cjk/wgbroker.exe?new+-access+top.main-page

其實不少網站都有實用物理的環節：

物理園-生活物理
http://www.phy.cuhk.edu.hk/phyworld/articles/index.html
立體電影的原理
http://yaox5d.myweb.hinet.net/pointview/dr-3d.html
物理與生活
http://phlife.7456.net/
科學人雜誌-科學馬戲團
高爾夫球上的小洞有什麼作用？
http://sa.ylib.com/circus/circusshow.asp?FDocNo=447&CL=8
彩虹為什麼是圓的？
http://sa.ylib.com/circus/circusshow.asp?FDocNo=491&CL=8

Revealing the Magic in Everyday Life (PHYS0607, HKU) http://www.physics.hku.hk/~phys0607/index.html
Defying gravity: The uphill roller（自動向上移的物件，拉去中間睇video，你就會好有興趣睇曬成篇文!）
http://plus.maths.org/issue40/features/uphill/index-gifd.html

磁場

要距離地球多遠，才不會受到地球的磁場影響？
兩個天體之間磁場會否互相影響？

A:
1. 要距離地球幾遠先唔會受到地球ge磁場影響?

理論上，離地球多遠都會受地球的磁場影響。
磁性物件之間的力是F = k q_1 q_2 / r^2 （其中q_1 和 q_2是物件的極強pole strength，r是兩者之間的距離，這方程的形式跟萬有引力的G m_1 m_2 / r^2 相近），所以極地球多遠也好，這種力依然存在，只會變得微不足道。

至於以地球的磁場為主的範圍（即是，在某個範圍之內，相較不同星球對該點的磁引力，地球的磁場的影響力是最大，例如，在木星，我們仍會受到地球磁場影響，當然木星本身的磁場影響力是最大），則稱為「磁圈」Magnetosphere。地球的磁圈，在面向太陽的一面的邊界 約為10-12 R （這裏的R表示地球半徑的長度），左右兩面是15 R，至於尾部則拖得非常之長，約200R。

下面是磁圈的圖片
http://space.rice.edu/IMAGE/livefrom/5_magnetosphere.jpg
http://science.nasa.gov/ssl/pad/sppb/edu/magnetosphere/images/mag_sketch.gif
http://www.uta.edu/physics/main/phys_research/space_physics/pic1.jpg

2. 咁兩個星球之間ge磁場會唔會互相影響到呢?
天體的磁場是由天體的電漿（即plasma 離子化氣體ionized gas）、流體（如地心的熔岩）流動而形成的，這些帶電的東西當然會互相吸引或排斥。
地球的磁場不是受到太陽風影響嗎？（注意：太陽風是太陽磁場的「產品」。）
參考資料:

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

為什麼地球磁場平均會南北互換?

A:
科學家對「地磁倒轉」沒有定論，有多種說法，我只擇其二解說。

說法一：地球外地核的液態金屬的流動是渾沌的（chaotic motion），有很多擾動（流動方向與「大方向」相異的部分），這些擾動累積下來，便令地磁整個倒轉。所以地磁倒轉的週期頗不規律。

說法二：地球外地核的液態金屬流到內地核。其中一些凝結了並一直沉積，並沒有流回外地核，累積多年，一剎那間像雪崩般暴發了，所以磁場便起了大變化。
參考資料:

http://en.wikipedia.org/wiki/Geomagnetic_reversal#Causes
http://earth.fg.tp.edu.tw/discuss/view.php?serial=1934
http://www.ufo.org.tw/news/2006/041406-1.htm

Chemistry

http://chemistry.about.com/od/testsquizzes/Chemistry_Tests_Quizzes.htm
Chemistry Tests & Quizzes

• pH of Household Products
• Everyday Chemistry Quiz
• Food Chemistry Quiz
• Bathroom Chemistry Quiz
• Crystal Growing Quiz
• Phases & Phase Changes Quiz
• Metal Quiz
• Rock and Minerals <= Not Recommended. I hadn’t seen the name of mineral names besides cinnabar,pyrite and quartz.

Suitable for F.3: -_-

• GED Chemistry Quiz
• Laboratory Safety Quiz
• Compound Names
• Element Atomic Number Quiz
• Element Symbol Matching Quiz
• Chemical, Physical, and Nuclear Changes Quiz (不過有問alpha,beta ,gamma radiation)
• Element Symbol Quiz (有些應該唔識，例如 Y=Yttrium, Cm = Curium, At = Astatine, Th = Rhodium, Tl = Thallium)
• Periodic Table Quiz

—Food & bathroom & Everyday Chemistry

• When you chop onions, your eyes can burn because a chemical reaction produces sulphuric acid.
• Urine tends to have a yellow/amber color. All of the following are names for a yellow pigment found in urine:
  • Hydrobilirubin
  • Urochrome
  • Urohaematin
• aspirin=acetylsalicylic acid.
• Vitamin C = Ascorbic acid.
• Hair gets its (natural) color from melanin.
• A tomato gets its red color from lycopene.
• Hot peppers get their heat from capsaicin.
• Bilirubin is most directly responsible for the brown color of feces.
• http://www.ul.ie/%7Echildsp/CinA/Issue49/qanda.html” target=”_new”>How do antiperspirants work? (antiperspirant = 止汗劑)
• The chemical known as thimerosol has been used to preserve saline solutions and vaccines. Thimerosol contains mercury. (The compound is being phased out from most childhood vaccinations.)
• BHA and BHT, which are used to keep fats from turning rancid, are two chemicals commonly used as preservatives in food.
• Chocolate and cocoa naturally contain relatively high levels of Cadmium and lead !!!
• Tums , Maalox = 胃藥
• You want some water to wash down the aspirin. If no one has used the faucet for many years , you may want to let it run for several seconds before drinking to purge lead from the plumbing/fixture. (History)

—Rock and Minerals

• Topaz is a silicate mineral of aluminium and fluorine .
• Chalcopyrite and bornite are common ores of copper.
• The mineral beryl is a beryllium aluminium cyclosilicate.
• The purple gemstone amethyst is a type of quartz
• sequence of stones is listed in order of increasing hardness: fluorite, quartz, topaz, corundum
• Tourmaline is found over a very wide color range, such that single crystals may be multicolored with different optical and electrical properties at opposite ends of the crystal.
• Orpiment is a compound of arsenic.
• Almandine, hessonite, pyrope, grossular, and demontoid are all types of garnet.
• Rubies and sapphires are both varieties of Corundum

—Others

• Types of Crystal: http://www.chemistry.co.nz/crystal_types.htm
• For some crystals it probably won’t matter whether you use tap water, distilled water, or bottled water, but for other crystals water purity is very important.
• When solute B is added to pure solvent A, the vapor pressure of A above the solvent decreases.
• You can grow a seed crystal more easily if you try to grow it on a roughened surface, like a cotton string or a slightly scratched glass.
• Alloys are mixtures of pure metals. The melting point of an alloy is usually lower than the melting points of the pure metals.
• In its simplest form, bronze is an alloy of Copper and Tin.
• The alkali metals have the largest atomic radii in their periods.
• Rust = Fe2O3 * n H2O (So it may say there is no hydrogen =_=”)

---

• What is the difference between ductility and malleability? (source)
  • Malleability 可展性; 可鍛性 is the ability to deform easily upon the application of a compressive force: making thin sheet
  • Ductility 延性 is doing the same with tensile force: being drawn into wires

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Economics, physics, chemistry

Economics:

• What is transfer payment? What is credit money? (Past paper in 1980s =_=”)

Chemistry:

• 為何gel 頭用那些mousse有LPG？ They are propellant. In room condition, butane and propane are gas. But under great pressure, they are liquid form. When they come out from the container, they change from liquid to gas.
• Why is it not advisable to use zinc-carbon cells in a digital camera? A lot of hydrogen will form around the electrode if the load is heavy. NH₄Cl can’t remove all hydrogen immediately. Then the cell can’t work. (From Chemistry Modern View) Picture

Physics:

• dioptor
• Snell’s Window
• Floaters
• In a cloud chamber, the track seen is made up of: water droplets
• When current passes through a solenoid, how will its length and radius change? Consider attraction between current-carrying wires. Radius increases but length decreases.
• Hold two fingers so that there is a narrow slit between them, and look at a light bulb through the slit. What causes the dark lines?
• Why is it impossible to observe things in the order of 10^-8 m by devices using visible light? Diffraction
• Why do the far end of a pool filled to a uniform depth appear shallower than the end near the observer at its edge? Diffraction

The last 3 questions are from Physics Vol 2, by Halliday, Resnick, Krane