買三第張大熊
英文中學會考試題預習專欄
物理科
(十八)
梁海明~
PHYSICSHLLAMES=
Solution.
33.la Xi )Sounas "may" "be "mane tuning forke.ga cun-
ing fork has two hard steel prongs. When
struck on a piece of hard rubber the prongs vibrata and a note of definite piton is given
cut. The prongs of a
a sounding tuning fork are seen to present a hazy appearance `ewing to
their state of wibration. Again, the water in
a beaker is violently agitated when the vir brating prongs are dipped into it.
(11) We put an slectric bell into a bell jer
the air in which is gradually, pumped out. As
air is being pumped out, we notice the sound
steadily got weaker until it almost disappear.
a
ed, although the hammer can still be seaa. striking the gone.
(b) Get 1 ft. be the distance of ‘A. From the cliTE
vft/aec. be the velocity of sound
34.(a)
When A fires a gun and hears the echo after 1 Bac..the sound has travelled at a distance of 2% ft.
2x
825 ft-
ft./800.
cliff
When D fires a gun, A heare an sono after 1.75 Bac
(2x825)/1.75 ft./ses.
2x - 22 --825
3.5x2x • 825
152
625
*
550
* 2 x 350
1.100
вес
Answer::fi) The velocity of sound 18 1100/
ft per seo.
lil). The distance or a from the olifa
18 550 ft E
ftae the least Bistance of the obse tacle from the observer to produce an echo. Since the impression o sound on the human- ear lasts for 1/10 th second. The abatanle- must be so placed that the time taken of a sound exceeds 1/10 th apnond to reflect to the observer.
Time for a sound to travel to and
the observer is 2x/1100 sec But thie should exceed 1/10 th seaand,
+
-2x/1100 > 1/10
> 55
ft.
Answer: The least distance" ssonld be 55ft:
@law-of=zeflection" of sound is the same.
That:18.
b)(1)
de reflection of light.
int and refiested waves and the nor→
the same plane and the angle of Ag #equal to the angle of reflecti
produced by the reflection of
σου το hard surfapé tuch m a wall or cliff. In
hat solo may be hang separately from he
sound it must arrive at least 1/10
Sipce mound travels at about 1100 The mininum distanse of the wall. must 55 rs.(**# 33(0))
Lasso Newton showed that the velocity of sound is proportional to Pressure Thua LE
Daneity
the temperature: ¡noreases at constant pressure the air will expand and therefore become less denge. The ratio wi21
ure vincrease, and, henge the velocity Of round increases with temperature
air is replaced by a censer g28, tna
dEČTIAREK, and hence the velo»
ratia.
bity of Coun
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the co
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英文中學會考試題預習專欄
化學科
(十八)
CHEMISTRY (18)
*王錦釗,
Il amount of each sotia la soparate" test= tubes and add dilute bydrochloris acid, to each.
#111 Rissolve to form a colourless solution
calcium chloride. But in the
of
tube containing ca cum carbonate, efferve will also take place and a gas is given off. The gas may be shown to poskrbon dioxide, for when
it.
in
Ron for the reaction between calcium hydroxide
to passed through a small amount of Lite-ukter |
test-tube, the lime-water will turn milky
and hydrochloric acid-
Ca(Oil), * 2RGI
CaC1,
Equation for the reaction between calcrum carnonate and hydrochloric acid-
Lacos
2HC1
- Ca(OH) ** Cacu.
1ide vaŝer
CU HU
[b]Puť a small amount of each solid is separate hard- glass teat-tubes and Rest hotb tubes strongly, ine Hangen flame
The selids in both test-tudes meit to Itquids the case of potassium chloride, no further che takes place But in the case of potassium
**
olourees gaa is seen to be given off, as bubb Ties through the uolten liquid. The evolved oxyzen. This is confirmed by placing a weakly gloving splint at the mouth of the test-tube. splint will be rekyndi eð
Heat
KCT
rnysical change from SOTIN CO
qui aLate
2KNO
Bolid Tr Cypr te chloi
Cuo
17. the trucezave contains mangalese dioxide, free, gas will be evolved. and is the solid disso❤ Ived in the acid Tue gus can be shown to be chlorine by cesti git with starcli puper dipped. potassium Iodide solution. The displaced iodide solution. The displaced loding vill turn blue. the presence BLarch
Mau
41C1
2K1
2KCF
211,0
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SEX DY HE
201
VERDER-TUM Z NI BAJAN
10 B00111on, the resique DLBINGO nitrate is neuted is an infusible white aid heud nitrate divas-a Tusible restines, which is
A
reddish-brown unen bot and yellow when cold.
To show that astric acid contatos oxygen, con- centrated nitric acid is poured drop by drop- into the bowl of a long clay-pipe. khen the stem is heated strongly, the acid decomposes The gases are
tube.
A
gas is obtained which can
Ponected over water in a test-
be shown to be oxygen as it will re-ignite a weakly glowing splint
·4ÉNO:
NO2
Brown fumes (which dissolve
in water)
(b) Dip a clean platinum wire in an aqueous adruSIOP
of copper nitrate, and put the wire în luminous bunsen flame; The colour of the flame will be green which indicates the presence of
copper
(c) Pase ammonia gas over red-hot cupric oxide
contained in a porcelain bost placed 10 8 com- bustion tube. A gas will be obtained. which can be collected over vater
2NH
Cuo
31,0
The gas can be abówứ to
be natrogen, for...it' answere negatively to all the common tests for gates":
(a) Heat some calcium carbonate strongly in a hard-
glass tube. A gas will be evolved which can be collected in 5 gao¬jay by downward delivery", The gas can be shown to be carbon dioxide because it turns Time water milky
CO
LIBRA
mane on sijueous sajut ten or ench suparance, and put a litis of each solution: separate test=" tabes To excli test tube, add caustic soda solution and heat gently.
The teal-tube-tube containing sodium entoeide vill
na ABZON Semical react Lundst
The test tube containing ammonium enioride gives off a gas which will turn damp red litays blue The gas evolved is ammonia
NH Lae NaUlk• NaCl • MIL.
Puti a small amount or each solid in separate test tubes, and heat. In both cases,
be evolved as well on an lavish
which will reguite a glowing splint.
rowingne w
In the test containing land nitraute "now decrepitation will take place
KAI(NO3)3 = ALU.
2PLINO,), - 2Pb0
6NO
oxygen
CO
Cao
Attach a piece or magnesium ribbon to a deflam grating spoon. Then take a gas jar of the gau llected, light the magnesium and plunge the podo into the gas The magnesium burns with some difficul
on the aides.
of carbon-see-ebta11
WELLEin maugaaṣNG ULUTTAG vien sage POLTRE
sium chlorate and beat the mixtury-gen herd glass test-tube until no further. action takes place. The residue in the test- tube to a mixture of mauganese dioxide, and DOLABI IUu chloride
2KC10 - 2KC1 • 3
Thèo, tue dixture is cool, add some concentrētēs sulphuric acid and heat gently. A green gas chlorine.
giten off: which turns starch paper- dipped in potassium iodide solution blue 2KC1
2K1
2850
MOSO
Iturne'. sEATU
blue)
Desvious for next Yeak
(a) Okkerida oge method for the large-scale eɣuraça
Lieu of Bulphuri
15) Describe the preparation and collect
several gus jars of hydrogen sulphid with powdered sulphur
starting.
Vel Describe expert's how the action of this
as a combustible substage; (b) as reducing agent, (c) as an acid forming maite State the conditions necessary for each reaction and the
(d) what volume of bydrogen sulphide, measured at D
and 760 am pressure is liberated by the action of dilute hydrochloric acid on 1.00 gms of ferrous sulphide?
(e) What percentage of free Iron as present in ferrous
hydrogen sulphide obtained by
Bulphide, if the "
the action of dilute hydrochloric acid on the ferous sulphide contains 10% hydrogen by volungy
Resonants.
Quality of a musical note:
estions
35. (a) Fing the frequency an Wave-length of the.
note produced when a card is held lightly acainst a revolvir 3 Gbg-wheel having 48 teave and rotating 150 times o minute. (velocity
sound 1120 ft. per ano.
(b)
wire one metre long has a frequency of 150 when stretched by 20 kgm(wt). State exactly how the frequency could be raised to 200: (1) by a change of length only
(11) by change ofension only
Calculate, the new length in case(1)land_the new tension in 028
Fork or
·Len string
colum
tube
[quency 512 18-herd over
tube of ametaz, 4 in. standing in
gradually raised out of the resonance with the fork is aktained Length of the tube has been withdraw from
How much Tuzoher out of the water muat the tube be raised for resonance again to decur?
string is set vibrating by plucking 11
the middle; (11) av a point one-quarter or
ngth from the end. Compare the frequenazes rat overtone in each case. Dray die ama te illustrate your answer.
connert flute closed at one end emits its
FATET OverDone, jy the vioraving column o
10 60 cm long, What is the frequency of this nate? velocity of sound 330 metrea
Two wiresof the same material have lengthni the ratio of 213. If their diameters
or the hakber:
be the ratio or their tenui
give a note an poti
5622.
AZANTIDELO: