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loktimmy09 2013-8-27 03:49 PM

transfer Q

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↗亢龍無悔↙ 2013-8-27 06:24 PM

Please take a look at your textbook and notes carefully before you ask these questions.



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loktimmy09 2013-8-27 09:03 PM

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↗亢龍無悔↙ 2013-8-27 11:52 PM

你應該係f2升f3自己睇書睇唔先上黎問啦

等第時教左唔明先再上黎問啦

loktimmy09 2013-8-28 12:37 AM

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thomas1126 2013-8-28 12:57 AM

第四題一睇就知係2010 HKCEE PHY LQ essay

其實你有無睇過張圖係點, 睇左就知道點demonstrate個對流

loktimmy09 2013-8-28 01:06 AM

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thomas1126 2013-8-28 02:25 AM

glass入面,一邊放candle, 一邊放joss stick

joss唔係重點, 重點係smoke

因為smoke睇得到

然後candle點火

之後你估下會發生咩事?

dustbus 2013-8-28 02:32 AM

2.點解沙漠有大既日溫差(-40C)但香港無?


沙漠D沙散熱好快,所以夜晚涼

loktimmy09 2013-8-28 11:18 AM

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thomas1126 2013-8-28 12:30 PM

你都可以咁講既

loktimmy09 2013-8-28 12:32 PM

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thomas1126 2013-8-28 12:50 PM

yes but why?

loktimmy09 2013-8-28 01:05 PM

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loktimmy09 2013-8-28 01:11 PM

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thomas1126 2013-8-28 01:29 PM

[quote]原帖由 [i]loktimmy09[/i] 於 2013-8-28 01:05 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370409191&ptid=22363602][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
the joss stick smoke is cooler so sinks ? [/quote]
你有無見過香既煙會沉?

但係呢度就沉左, 點解?

你要講埋個張圖個set-up有咩特別

令到香d煙會沉

第1題應該同specific heat capacity有關

loktimmy09 2013-8-28 01:47 PM

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thomas1126 2013-8-28 02:51 PM

你要demonstrate "convection current" 何謂convection?

第一題你唸下specific heat capacity 同temperature有咩關係

dustbus 2013-8-28 03:12 PM

其實關heat cap事咩??
實際佢地都會達到thermoal equilibrium
佢問點解感覺熱D

係咪因為你接觸湯既contacted surface比接觸麵既contacted surface大,所以熱D

loktimmy09 2013-8-28 03:48 PM

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thomas1126 2013-8-28 07:42 PM

[quote]原帖由 [i]loktimmy09[/i] 於 2013-8-28 03:48 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370419190&ptid=22363602][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
對流 兩個向上升既圈相對住  我就係get唔到點解會有兩個圈


low specific heat capacity 咁 temperature易升d
但麵比湯既specific heat capacity 唔係仲低咩 咁點解湯會較熱? [/quote]

其實呢度得一個圈.

重點要講三樣野,

1. candle個邊d熱空氣向上升左

2. glass lower part 有個洞 <---因為只係upper part separated by a cardboard

3. 所以joss個邊d空氣會通過個洞流去candle個邊 i.e. smoke向下sink


第一題其實我覺得兩樣都關事

heat capa 你應該咁唸:low specific heat capacity 咁 temperature跌快d
湯同麵一既時候, 就會係equilibrium

麵一離開湯去口既時候

temp就跌得好快 (所以你吹幾下就食得)

所以感覺無咁熱

//或者: 麵係口入面既時候temp會跌快d

湯係口入面就跌慢d

所以個feelings last longer

contact surface都可能關事

湯浸晒成個口

麵店得少少


其實你講得有道理就ok

loktimmy09 2013-8-28 07:47 PM

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thomas1126 2013-8-28 08:06 PM

yes

dustbus 2013-8-28 09:01 PM

[quote]原帖由 [i]thomas1126[/i] 於 2013-8-28 07:42 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370433888&ptid=22363602][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]


其實呢度得一個圈.

重點要講三樣野,

1. candle個邊d熱空氣向上升左

2. glass lower part 有個洞  [/quote]

haha your answer 合情合理D:lol:lol
[quote]原帖由  於 2013-8-28 12:57 AM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370383661&ptid=22363602][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
第四題一睇就知係2010 HKCEE PHY LQ essay

其實你有無睇過張圖係點, 睇左就知道點demonstrate個對流 [/quote]BTW師兄你記曬邊年有咩題:smile_41::smile_41::smile_41::smile_41:

[[i] 本帖最後由 dustbus 於 2013-8-28 09:05 PM 編輯 [/i]]

thomas1126 2013-8-28 09:59 PM

NO , 因為我係個年考先記得 :smile_o03:

Ron~ 2013-8-28 10:29 PM

You feel that the water is hotter than the noodle even when they are of the same temp. is not necessarily related to the specific heat capacity.

The main reason is the ability of termal conductivity. An object with higher termal conductivity means it has a higher rate of heat transfer. The water has a higher termal conductity than that of the noodle as the noodle can be treated as a good termal insulator (common sense) so that heat from water transfers a higher rate to you tongue, you then “feel” that the water is hotter.



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thomas1126 2013-8-28 11:27 PM

[quote]原帖由 [i]Ron~[/i] 於 2013-8-28 10:29 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370444806&ptid=22363602][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
You feel that the water is hotter than the noodle even when they are of the same temp. is not necessarily related to the specific heat capacity.

The main reason is the ability of termal conductivity. ... [/quote]
佢個講法係最準,

你"感覺"到熱d

唔係因為佢溫度高d

而係佢比heat既速度快d

即係heat transfer per second 高d

而[size=3]heat transfer rate by conduction有4個主要factor[/size][list=1][*][size=3]temperature difference[/size][*][size=3]length[/size][*][size=3]cross-sectional area = contact surface area[/size][*][size=3]material = thermal conductivity[/size][/list]
[font=Helvetica, Arial, sans-serif][size=3][/size][/font][font=Helvetica, Arial, sans-serif][size=3]另外d湯仲可以transfer heat by convection[/size][/font]

dustbus 2013-8-29 12:11 AM

btw諗極都唔明點解火牛係黑色?:smile_27: :smile_27: :smile_27:

Ron~ 2013-8-29 12:22 AM

[quote]原帖由 [i]dustbus[/i] 於 2013-8-29 12:11 AM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=370452646&ptid=22363602][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]btw諗極都唔明點解火牛係黑色?:smile_27: :smile_27: :smile_27: [/quote]The only factors that you can think of are conduction, covection and radiation.
The transformer is always plated as black surface since it is related to radiation only. Of course you may also think of conduction or convection, but the reason for black surface is mainly relevant to radiation.



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dustbus 2013-8-29 02:15 AM

haha 比番老師添 唔記得左顏色同radiation有關 thx



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