其三張六第
第三年巳乙
WAH KIU YAT PO
一九六五年度
考試題預習
R.
I
V
物理科
(廿一)
•
,陸永熾,
Iftions 16 the combined resistance
V volts, the total p.1. across
Them, and
PHYSICS (21) By Mr. Luk Wing Chee
I amperes, the current passing.
V - TH
V
1
Ara
J
IR
1RZ
- Sum of individual ́p.d.s, scross R, and bo
(same current passing through
a. and R.)
2. 80lution
(a) If a charged rod is brought mar to two indulated uncharged metallic bodies A and B which are in contact
the two bodies will become charged Like charges repelled to the remote body,8 and ablike.
charges are attracted to A.
in the neighbourbood, of the inducing charge rod, the two
bodies are separated,
The two charges on A
sad B are known was induced charges. The phenomenontis kaovn na electrostatic induction.
(b)
1. The two ingulated metal
spheres A and B are
placed together ao that they touch one another and thus form a ainele conductor.
2. The ebonite rod is rubbed with a piece of fur la order to produce electri- fication by friction, ebonite rod becomes ne- gatively charged.
While
CHREGED
Charge
A
Insulated uncharged conductors
thonite The
3. The charged ebonite rod is
brought near to A. As a result, a positive charge is induced on A and a negative charge on B.
4. Still keeping the charged rod in, position, sphere B is moved a short distance away from A
5. The charged rod 18 DOW re-
moved anu A and B are tested for charge.
red
cantacy
A and B
separatecr
4
n = B
B2
I
The o.d.s.Tor R, and H are equa),
封
日期星
6日八十月四年五六九一饜公年四十五國民中
一九六五年度
試題預習專欄
數學科 (廿一)
·容明健 •
Mathematics
Solutions to lost week
B exorcises.
→ AQUBEA
Long
apol at a corner
rope which is 50 yu
che dank ey
A donkey is tetherae to a field of 78 yards length, by a what percentage of the area of the field can reach? what lengh of rope is required for the donkey so De able to reach nalf the field?
78 x 1 sq ya 6084 na yd
Area
of
field
Area the donkey can reach
with of a circio
2500
ན སྐ*
Percentage
of
field
•
renco the donkey can
2500
1878 100
22.1% lapp ?
Length of the rope.
it be the
+ TR2
A2
* (Area of the real
* 1/2 608". རྞྞཎྜ ་
50 vc
3853
-
1
bu B
1
V2
12
R
62 yd
I apo 1
Q.2
-
V
Sun of individual currents
A conical base of area
tent of capacity 516 ov 154
ft.
f. + Find in an
f
on
CHA
ATA
F
Virzular
Canvas7 Di ne
V
2 Ba
-1
(Since V
1 of Rose
*ant
4 b16 cu.
*
• 154 99. 1 $
Since
1 e
Voi
= 1/3 basex c
618
• 1/3 x 15tx b
I where 19
the ht
10
cene]
h
*
* 1
· 12 ft
K
11alors
resistance
19 (1.
E
if is parallel, t becomes
fe
where
radius
22
on each are
10 series.
The combined
1) obros
3 obas,
me
start melghat (1)
-
√2.2
· 344449
- J193
-
T
2
154 54
13' x
→ 7 ft
of bage)
A WILL
become positively charged while B becomes Degatively charged.
Inducing charge.
removed
(b) An electrophorus consists of a circular slab of insulallog material, together with a brass disc on an unsulating handle. Flie ebonite slab. 18 given a negative charge by flicking it with a piece of fur, and then the brass disc is placed on Lop of it. This resulte in positive and negative charges becoming induced respectively on the lover and upper surfaces of the brass disc. (The disc does not become charged negatively by conduction, since it 18 never quite flat and makes contact
ith the lab only at two or three points.} The brass dist is now earthed momentarily by touching it with the finger so that the negative induced charge is repelled to earth. removing the disc from the slab it is found to be positively
harged.
This charge may De transierred by contact to other hos Ce ind can be brought back to the diec and recharged without Clicking at with fur again, In this way a cousiderable large
barge may be obtained,
insulating
handle
Brass diss
Ebonite sfab
Charges induesp
on brass dica
Brass dise earthed
·Brass dice
refered
(1) When an insulated brass sphere of positive charge
is brought into contact with the outside of an insulated hollow conductor, it is charged positively.
The charges reside on the outside of the follow aphere on removias the brass sphere.
(11) When the charged sphere is in contact with the 10- side of the Hollow conductor, it is also charged positive- ly and with charges reside on the outside also,
The fact that charges reside on the outside of the conductor can be teated by using a proof-plane with à gold-leaf electroscope.
*
[6) Advantages or a lena accumulator:
(1) This kind of cells can be recharged after being run down by passing current through the is from a dynamo'er other source of current Caicanly}
(2) It has a low, internal resistance and hence can give
large current with very little drop in terminal potential difference..
(d) A fully charged lead accumulator consists of:
Electroder:
Positive plates:- Lead perezia. (Pho)
Dark chocolate brown in colour. Negative plates:- Spongy lead (Pb)
Sia ta grey.
and distilled water 15.6.
After discharging it become #j
Positiva platea:- "Lead sulphate (PbS0,
Lighter brown.
Begative plates:- Lead sulphate (PbS0)
Lighter gro
Electrolyte- Bado, and more water (5,0.
1.18)
•1.25
Three precautions in the correct maintenance of accumulator (1) Give routine charge after use Give extended charge Do not leavesa, at least once a month or fortnight discharged cell idle.
(2) Keep the electrolyte level about 3/8 inch above the
plates.
es. Take regular 5.0. readings and make good. evaporation losses by adding distilled water, Add acid only if acid is spilt.
(3) Keep the vents clear and the terminais clean and
lightly greased to prevent corrosion
solution
(a) The force or tendency of driving an electric current throu
conductor is called an electromotive force." tive force (enf.) results from the fact that strona repel each other, Electrons, therefore, Lond to be repelled out of bodies that have a large concentration of electrons and to enter bodies that either lack electrons or have very few excess electrons, if two bodies with equal concentrations of electrons are connected by a conducting no electrone will flow from one to the other, there
wirew
E constant tez- The current passing through a vire al perature is proportional to the potential difference between its ends. This known as Ohn's Lằvị
The resistance of a conductor is the ratio of ins potential difference across it to the current flowing through it
(1) Resistance, of two conductors connected to deriep:
{s}
3
x
÷
onn
6 cells
trohms)
E 12 volts
r='o. 6 ohms,
V = //.25 volts
www.
9.chms
current Flaving
9.6 0.1 op .23 cop
E=12/
94
Z
6A
VID 29 v
current in y-on co21
4.3.
Area
OF
che tent
17 RO fe
Sector VAB
1/2 42T4
11 base x height)
A
·
X7X1184
303.6 53 rt
vide anti 11.8
bath is ft. long and 30 ft. Swimming
20 ane end to 7 ft. depth increases uniformly from 2 [x.
The cross-section of the delivery pipe i at the other
flows full bore circle of diameter 6 in. and the water
2 ft.
par through it at uniform speed of
takan to fill the hath the Time in hours.
sec Find
Arsection
01 the batt
=
#
tupper base lower baseline) $(3-7)(90)
450 sq. CA
PLAN
CLEVATION
1 K-SECTION:
sq.ft
of bath capacity)= X-Section X breadth
(05 The pipi
Area of pipe
150 x 30
13300 u
ú in. L ---2
22x(1)2 = 7216
Speel or running water thro, pipe • 2 ft/sec
Yol of water
into the hath per set
1
zx 2
cu.ft.
22 x 2 x 450X30X730BRE
the bath ザ 22 x. 2
Fors are
0
150X 3087 116
2212×60×60
105
•
M
the exercises for this week:
ABGD 13 parolielogram.
WBLIC LIBRANE
dacross
1 x 6
2:
VoLGMe per
It the mo
GOLF
of this main currant (11)
D
che
main current (1
121
225
sup
Prove that
AC2 + BD2 2 A82 + 2 Bc2
ara mid-points of AG, BU
4xy 2 AB2. 802. Cu2.. m2 - AC2. 802.
4.2.
ABCU IS a quadrilaterais p Prove that
J.M.
U is a point on
the side BU of Trig, ABC such that BD=2DC
Prove that AR2· ZAC2 = 6 CD2 + + 3 AD2
香港商業廣播電台
第二点:四月十八日下午五時半至六時:
二個五月一日上午八時卅分至九時
学堂”第三十八
第二次有獎測驗者
(2.)8722
50.18
(3) 8
632×3×7x11x17
(8)213747 6 › 8 - 12 - 16 - 24.9.48 (10) 180
3
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(16) 1003 EL
(19) 951 SEAT
(II) 165
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(20)
升中指導節目算術科
播出日期有
€ 110
(4)88
(7.19 23 53 › 62 (9) 74.
(12)1.254
(15) 3
(18) 2010
connected across une battery, it rands
volta or 11.25 volta
(21)
(24)2744方时
(22) 8.
(25) 14-1
(26) 7:5.28
(27) 65%
(28) 308,426
(29) S-
Explain what la
(30)
(33)1方尺92万于: (36) 24
(32) 87.54%
of potential drop of the external resistors. For the former case it ceads
for the latter case it riade (24 x 1 velts or 10.29
volte
estions (22).
(a) State Faraday a lave si electroivala
meant by an electrolyte (b) A 6-volo battery je connected in series with a torch bult
and two platique electrodes dipping into a glass võnnel The glass vessel is filled in turn with
(i) distilled water (i) mercury, (iii) aliute sulphuric acid Explain what happens to the bulb and to the liquid in each case. Draw a diagram of the carbuit
(c) in finding the error of an Ammeter, it is placed in series
with a silver voltameter When the current is adjusted so that the ammeter reade 2 amps. it is found that 8,2 ga of silver are deposited on the cathode in 1 hour. What Is the error of the ammeter? Ec.e; ofalvar ia 0 001118 coulomb.
2, (e) braw a circuit diagram of a metre-bridge for measurinn
Give the theory of the method.
resistance
b) A metre bridge in used to measure an unknown resistance.
A standard 2 ohm coil is placed in the right-hand gap and
The the unknown resistance placed in the left-hand gap. anil point is found at the 48.4 on, merk Calculate the value of the anknown re
resistance. Where would the buil point be if the resistances were interchanged?. explain how an ammeter givings full-scale deflection for a current of 15 mA., and of resistance 5 ohms. may be converted, to a voltmeter to measure up to 6 volta Calculate the value of any resistance required,
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