1968-03-13 — Page 14

二肉鲜

日至十月二年申戊震器

WAH KIU YAT PO

D968 英文中學會考試題預習專欄

Solution

物理科 (二十)

陸永熾 •

37. 'Solution

Physics (20)

(a) A gold-lsar electroscope, in its simplest.

form, consists of a metal rod, à, terminates with an attaching gold leaf, L. Its upper

end is widened as a metal diso, C. The rod. passes through an insulated block, S, tightly nold in a metal case or a glaas conical flask, F. The disc is outside the TLABK,

儻

三期摄

(a) Ohm's Law states that the current passing through a wire at constant temperature is

proportional to the potential difference / between its ends.

it may be expressed ası

Potential difference

current

I - y constant)

This constant varies with different

wires. For a constant potential difference,

a higher resistance will pass a smaller current and a lower resistance a large current, Thus, the constant measures the resistance of the wire. It is re-expressed asi-

itesistance -

Potential difference

current

The resistance of a wire is the ratio of the} potential difference across it to the, current flowing through it./

b) Resistance in series '

R. www

Ra

R.

育敬備證

僑

教

育

政府計劃在今後五年内

建五間工業學院

接受工藥那綠機會,政府應導教將現有之

一、此五間工燊學院,將可收容四千名學生 關心入士指出:無使本港學生有挺多~~ 日數字,在任何情形之下,仍是是不够告衫貴的腎科。一、一外關係」。 | 於蛰州模蟷缺乏工業團·門人才,四千個學 中共四大文件,一九六七年的中共對,可馬中原,朱亦凡 一入學。但關心此方面發展之入土則謂:參刊」三月號出版,刊棠與交通運顧」,「,林文月「答客間」張十元。體長池艾事將云。 | 要建立間上莱學院,以明娩工業專門人材 祖園月刊 「劉年的中共畫務」,「」,顏元叔「乾認的好車元,書局部,女國式所移,請轉否 一、俞大料、羅盤林、 霸月一九六七年的中共工思想在乾截的不懈,方言。打開全年嘉,著仔架神糁院嫣激的

日三十月三年八六九一瑟公年七十五國民中

平亦嫌太低 生所佔比例太少 且本港工業人才訓練水 關係人士認爲在本港中學生中 工業學 本港現有工業中學生三萬六千八百名

工業所需。

(#)

六有三萬六千八百名學生,在工業中就發展 〔怫顉〕棂濶有閼喾易統計,本洲現一概崦有門球之工糪人材。

十一背護者少 一學就頂之學生,人數之少,殊使關心工箂 目前中學生總數,共爲十九萬人 三,千九百七十二人。在比較之下,在工業中一發铋之壽現,再排以自熱工業人材調表之 「啪之地位,懸在工業A材啪连荁面,有更 本Ä者希望能在世界上英中我更受到 關心工業,黃當然人士指出:

水平,實難與其他各工建造醫科宅泉一日 繼續辦春季班 教師會攝影組

產

班

組

品產港香識

心

【觀

認

中列陳品產港香

體集生學迎歡

一項進程。 工業教育程度,將爲本港工業發澳中之一, 有國人士都用:本瑞若不努力改島其產學 美之永久性的香糖素品優列中心。 ,發應予以修改,伸其見朗適應發展中之港 香貿易發展局簡慧,准許各中小學學生; 工業中學學類織完,同時將所教授之料 忍香歡 參的品質優良產是起點,致育賞影已商很 ,節日自上午九時至下午六時止,怒出

由教師 租之下,集參照該局設在海運大

〔特轾 )爲使學生們加桀器誊本传承摊 巷陳集的在公觀。該通營內容有以下各點:一、查學生橫過馬路,亦殊商險,與當局决在帮 康品陳列中心。此中心皆放時間爲週七天便學生往來。 海貿易發溉岛於濕運大厚設有永久性發樓之一 心事業前疪馬,英熹一度行人天橋,利 並希望各校校長齡勵學生利用此機會,來學生散於馬路两旁,眞女人如棄之感。 敎育司署昨爲此事,向各校發出適告, 作上下午班活。每當學校上學及放學時, 校歌家,悔校學生動輒千百人,亦有穿 〔新亚肚山半山羅賴便臣道口,有學。 买心女書院前建行人天橋 上課下課交通擠

羅便臣道學校多

本堂工業插屁,正方無沉,工業人

據悉:當局有計劃於午後年內興 日「村游文之急,已是一件拆爲明照之掌。怀 黑多之工棠萬門學院。據消息來源透露:一師會影照冬季班飛影比賽在展與會,一星期前,致百九冠海運大厦二三七金香致易發股馬執行幹事, 冖特别乚香裾酸,行會機組員| 「繪在城市於低源之萊籬無中,香港姁 有關間將會考慮在五年之內,最低限度 劉衡,然珽於去年户精岿滿,將於今。學生人號以四十人爲限,並須由教師一位榮熊前往。 睿業滢品不下六百頸。 三、各校校長摭案於利用此價會。欲前往參案之基撕,希 前往參觀,但學生對本洪流蜆繁多、品質供系之照品有限鳥線。 二、茲經典鵲間洽定,可接受學校團旗

品

速校目前爲安全。. 相信一两個月即可完工,願時學生往來, 戸工程現遠行株土,建躉,

來讓,無顧及拿州苗,同時車整 不致放在行人路上,有開學中往遠。 殼一度,另在低豆還關上面制大遊學獻。 又羅便臣遠處取羅斯新界處新建石

Label

P

Parts

metal disc

metal rod

gold lear

insulate support transparent flask

wire or finger

Function

collect charges

conduct charges divergence

: detection

insulation

isolate the lear

from air

circulation:

outside

to earth the case.

To test for the sign of the charge on a dodg

The gold-laaf electroscope should be charged either positively or negatively first. The tent body is cautiously brought down from a good height. The divergence of the gold-lear is carefully examined. The possible effects of the leaf divergence is tabulate as follows z

charge on electroscopa

charge brought

near

-

effect on the leaf divergence

Increase

Increase

Collapse but diverge again.

Let R ohms be the combined resistance

Yand

81, R2, R3 ohms be the individual

resistances/

V volte be the p.g. across Ri, Ez, and Ri

"

#Therefore IR .

Conclusion

酹

B2

M

# Ba

典

*

current through

(in series)

T2hy - IgRg (Camt

I(RY

*

我2

R * By • R2 • B3

The combined resistance of several

2

resistances joined in series is equal to the algebraic sum of each resistangé and is · always greater_than_each_individual.

Resistances in sara Idel

V

-

--

uncharged

-

do -

Collapse

I

篇

()

枚,用時頒發獎品。形毒東在中央工作重 公時間接受參加登記央關於對黴歸召開「十餘間,內容豐富。其開始」、亦頸之介 班,在三月下旬關線雜的「意見書」出的R嶲新氣息大型一中獎推話」,何一 出版消息克文章的上」,來。是雙月刊,低册師說人員及憐士梦 |,仍【董雪峰老師數 三、誠實的「二月的文學雜誌。創刊號 葉形小說家被爾斯 j2 天主教梁教组 現鸩起丽根果然赛事 撒上的講話」;二、 是台灣知餓青年,辦的「卯」、黃士乛[鏖戰邁 斯 四月間,奉行秦帝廟|九六六年十月升进 草原雜誌 紅 林名作演一 代表——香港仔畫版 尤大」的意見的通報,要日本:余光中「在「統懟記」等四十餘定三月十五日為釋。

戎佑民俗文革」,邱文程四五一五號。

被浪遊訊」,發定本

| 啤復活窗出版,期

Genalusion

We

An increase ́ın alvergense cocure when aharge on the electroscops and the test charge are

of the same kind.

A divergence after collapse shows that the enarge on the electroscope and the test charge are of different kinds.

When the body is uncharged, the electroscope, will be neutralised and the leaf collapses sompletely.

((b) in Electrophorow or "charga-carrier" consists) of an ebonite dise ▲, and a metal plate B with an insulating handle H. The dise A is rubbed with a piece of fur, and becORES negatively charged. B is then placed on it and momentarily touched with the finger. Finally ¡B is removed by means of H. On testing, B is.

Zound to possess a positive charge.

-

-

VI

+

13

V · yy (in parallel))

AKONG PUBLIC LIBRA

B ie placed. on A, making

little contact, e repelled to upper surface, with →

shezge near A.

B is earthed.

e (- va) is led away leaving + ve charge behind

*

M

•

-

Conclusion

•

V3 Ra

R2 R3

Law)]

The combined resistance of mrallel combination of resistances is equal to the sum of the reciprocals or individual resistance and is always less than each individual.

3 tran

(c)}

E. ohms

1,

A

y volls

The combined resistance

* n ohms,

• (6

+

• ?

3 x A

3.4

Ohms

Ohms

inger touches B

1+ we charge is thus antarily only. It is .......... transferred to other,

wed before B is lift. bodies.

The metal dise B may be charged for many time without recharging A. This may be explain with the conservation of energy, The charge (electric energy) is not out of

thing, Mechanical work must be done against)

force of attraction between the charges B, and this werk besomes converted

By Ohm's Law

The current through 6-ohm resistano

9

74

63

*

52

1.21 8mm.

The currents in 3- and 4-qhm resistances are)

ly and 12

12,

and I

1.0.6923

-

*

52

-0.518

The potential difference between B and C

·

1 x 3 - 2.00 val ts

ans. The currents passing through ów, 3 ano

4-ohm resistors are 1.21, 0.692 and 0.535 respectively.

The D.d. across BC is 2.08 volts..

Questions for next week

39. Describe a dry cell and indicate one advantage

and one disadvantage of using this type of cell State the factors which de tarwan is interna) res istance.

Two resistances of 4 and 6 cha in oarallel are connected to the terminals of « battery consisting of a dry cells, each of Metal. 1.5 volts, in series. If the current in the 4-ohm coll is 0.6 amp. find (a) the current in the b-ohm coll, (b) the internal resistance of the battery.

40. State the laws of electrolysis and define the

terms anode and cathode.

Describe an experiment to détermine how the mass of copper deposited in a cepper voltmeter varico with the quantity of electricity passing through it. Give a circuit diagram and full experimental details.

An electric wrrent passes through two voltmeters in series, containing copper sulphate and silveP nitrate respectively, What is the mass of silver deposited in a given time if the mass of cepper / deposited in that time in 1 gu? (At.wt. of copper is 63, at.vt. of silver is 105, valency of sopper is 2, valency of silver is 1.).