第二第强大第 1十三月三年午丙层复
SAFARI KIU TAT
華僑教育
*270001
(4 x 27.4
会
試題預習專欄
=246 C.p.9.
#
(十六)。
When both are"soundˇtøgether a boat frequency of_{r} will be heard.
2
J
PHYSICS (16);
Lamm • Frequency of the air buba » 250 0.0.9.\
Frequency of the 00,-tube - 246 6.p.s.”
By Mr. Luk Wing Chee
If i
4.
(a) Factors affecting the velocity of sound in air
(1) Wind
Wind may alter the velocity of sound in air. sound is in direction of the wind, its velocity is greatly increased. If the direction of sound is into the wind. it will be slowed down.
(11) Temperature?
(111)
If the air temperature increases at constant pre- ssure the air will expand according to Charle's Law, and therefore becomes less dense.
. Since the velocity of sound is proportional to the square root of the ratio of pressure to density an increase in this ratio, therefore, increases the velocity of sound in air.
Pressure
In accordance with Boyle's Law, the pressure of a fixed mass is inversely proportional to its volume. Thus, at constant temperature the ratio of pressure to density will always remain constant, however much the pressure is decreased,.
(b) As 50 holes are uniformly spaced on the disc and the disc
rotates 300 reva. per min. In one sec., it rotates 300/
Frequency of note produced • 50 x 300/
revs.
250 c.p.s3.
Ans. The rotating disc emits a note of frequency 250 c.p.s.
-
日十二月四年六六九一磨公年五十五國民维中
育教倍●
英中產試題預習專欄
化學科
(TA)
Q
王錦釗。
CHEMISTRY (16)
Frequency of the beat
- 4 beats per sec.
The incident wave and the reflected wave of a vibrating substance combine to form a stationary or standing wave vibrating in a series of equal sequents.
Q. (a) Chlorine displaces iodine from a solution of potassium
iodide, and it is this displaced iodine which turns the solution brown.
}
+
2 KC1 I
Cl2 + 2 KI (b) Hydrogen sulphide reduces brown ferric chioride in aqueous
solution to ferrous chloride which gives a pale-green solu-
tion,
The hydrogen sulphide itself is oxidised by the ferric chloride to sulphur. which is deposited as a yellow solid.
"22 reulz. = 2 FeCl2 + 2 HC15 (c). When sodium chloride is dissolved in water, there are two
cations present in the solution, sodium ions, Na from the sodium chloride, and hydrogen ions, H, from the water. When an electric current is passed through the solutions, both cations migrate towards the cathode, where the hydroge tons are chosen for discharge.
7
A
The points where it remains at rest are called nodes (N). Between each pair of nodes where amplitude of vibration is maximum, an antinode (A) occurs.
H* .
H
= H
H ·
12
(d) Chlorine possesses a strong affinity for hydrogen. When a piece of cotton wool soaked in warm turpentine is dropped into a gas-jar of chlorine, the heat of reaction is great
nough to cause the cotton wool to catch fire.
帛
C10 H16 turpentine
8 Cl2
= 10 C
16 HCl.
(e) When ammonia gas is passed over heated black copper oxide,
it. will reduce the copper oxide to metallic copper which is reddish-brown in colour. oxidised to nitrogen,
colourless liquid.
The ammonia itself is colourless gas, and water, a
5CuO 2NHz . 3 Cu + 3120 • N2
Use
To galvanise fron
To make electric cables
To make aluminium alloys which are aeroplane construction..
all acids taste sour
(11)
An acid will turn blue litaus red.
used ir.
G.2 (a)
(1) zinc
·£4 ft.
copper luminiu
Length of pipe |
| Wavelength of note
Frequency of note
$1.20 8
(b) (1)
140/c.p...
4500 14.
Let x be the distance between A and B
Velocity of sound in air)
(-1120 ft/seo.
Time taken for sound to travel from A to B is
Time taken for sound to be reflected from C to B 19
1120
me interva)
1120
9000 2x}
EXA
* 2 x 1120,
33.80 ft.j
[Ang. The frequency of its fundamental note is 140 cipt
(11)
Length of wire 】 - - 130 cm.)
and 1
21
(Ane The distance between the snips is 3380 rt)
It is divided into two sections,
Frequency produced by first section 1
The above diagram shows the two tube of lengths, L. 68 cm
27.4.cn respectively, are naving their Fundamental modes
bration.
Velocity of sound in air
340 myseo).
Vo 270 0/86c.j
Frequency of fundamental tone in open Tube
Islosed
11
u gecond
KONG PUB
Since
(17 117-1200
100
2-1-100)
1-201
(111).
LIBE!
An acid will react with a base to form a salt and water
only.
An acid will react vigorously with carbonates in the
cold, with the evolution of carbon dioxide.
Dissolve a small quantity of the soluble lead salt in some water in a test-tube. To the aqueous solution, add dilute hydrochloric acid. A heavy white precipitate of lead chloride is formed. Digest a little of this precipitate with some water in another test-tube and beat. The precipitate soon dissolves as the water boils. Dissolve a small quantity of the soluble iron, salt
in some water in test-tube. To a portion of the aqueous. solution, add ammonium hydroxide, a green gelatinjus precipitate indicates a ferrous salt, while a brown gelatinous, precipitate indicates a ferric salt, The precipitate, obtained in either case is insoluble in excess of ammonis. If the substance is a ferrous salt it can be confirmed by adding a solution of potassium ferricyanide to the original solution when a dark blue precipitate will be obtained. & ferric salt gives a dark blue precipitate with potassium ferrocyanide,
Dissolve the chloride in some water in a test,-tube- On adding silver nitrate to the solution, a heavy white precipitate of silver chloride is obtained which darkens. of exposure to light. The precipitate will dissolve in armonia solution, but is insoluble in dilute nitric acid:
Make an aqueous solution of the sulphate in a test- tube.
Acidify the solution with hydrochloric acid, and then add barium chloride solution. A white precipitate of barium sulphate will be formed.
To an aqueous solution of the nitrate in a test-Lube, add some fresh prepared ferrous sulphate solution. Then add some concentrated sulphuric acid drop by drop gown the tube. The acid will sink to the bottom of the test.
tube, and a brown ring WILL De formed at the junction
(c) (1) Manganese Gioxide
of the solution and the acid..
When concentrated hydrochloric acid is, heated with manganese dioxide, it is oxidised by the mananese dioxide, a black powder, to form a green gas, chlorine,
Mn 02 + 4 HC1 = MnCl2 + Cl2 + 2850 Sulphur Trioxide.
Sulphur trioxide is a white solid which will dissolve in water to form a solution of sulphuric acid. Sulphur trioxide is called the sulphuric anhydride. 50 H2O H2 SOL
ii) Hydrogen sulphide
Hydrogen sulphide is a colourless gas which will react with lead nitrate solution to form insoluble lead sulphide, which is black in colour,
H2 S + Pb(NO3)2 - PbS + 2HNO
Questions for next week.
Give one example of the use in the laboratory of each of the following reagents:
(a) Silver nitrate, (b) terrous sulphate, (c) potassium iodide, (d) ammonium hydroxide, (s) potassium ferricyanide, (f) lead acetate.
Describe chemical Lesus, two in each case, that would distinguish between: (a) nitrogen and carbon dioxide, (b) oxygen and nitrous oxide, (c) hydrogen and carbon monoxide. 18.75 ml of N/10 hydrochloric acid are found to react exactly with 25 ml. of a solution of sodium hydroxide. Calculate (a) the normality, (b) the concentration in grams per litre of the sodium hydroxide solution. If this solution had been l prepared by dissolving 0.90 gm of damp solid in 250 ml. of Lwater, calculate the percentage of noisture in the sample.
the open tube!
the closed tube
x68
Ane. The bridge must be placed 40 cm.. from one end.y
Questions (17))
1. A sonomator wire has a stone hanging from the free end of the
wire which vibrates with frequency of 500 c.p.s. If the stone le immersed in water, the vibration frequency of the wire becomes 400 cp.s. What is the specific gravity of the stone?
What is the tension in gm. wt. of the middle C string
requency 270) of a piano? The length of the string-ia
the diameter is 1 mm. and the density of the
which it is made is 7.8 gu, per c.c.
The third overtone or a pipe cisea at one end has the same frequency as the fourth overtone of a pipe open at both ends If the open pipe le 70 cm long, how long is the closed pipe? 4. Two laentieri wires both have tensions of 5 kg.t. and when
plucked in the middle, both produce a note frequency: 250 c.p.s. If the tension in one wire is now increased by 200 gm.wt., What will be the beat frequency when they are plucked simultaneously?
A swimming boy heard a distant explosion in water and 2.65 seconds. later he heard the same explosion again with his head above. water. How far apart is the explosion?
Velocity of sound in air. 3) matree per, sec, in water 1490 metres per sec