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1969 95%
(e) Since
REFERENCE LIEF
19 MAR 1969
報日僑華
CITY HALE
三明星日九十月三年九六九一公年八十五國民華中
25
(2)
where e is the and correction
7y is the wavelength
(2) = (1) (l2 − l
The ratio of the tension should be 25 to
物理科
(二十)
陸永熾
PHYSICS (20)
[37.(a) When two waves travel in opposite directions
through the same medium, they will always
combine to produce sero displacement at some
points. These points are fired in space. They do not move along, although they are produced by the intersection of two travelling waves. The resultant wave form is known as stationary standing wave form
(N)
(N)
where V12 Que velocity of sound
ia the frequency of the tuning fork,
(d) The fundamental note is 275 par sec. Its first
overtone is 550 per sec, which doubles fundamental note,
This indicates the
organ.
the
pipe is an open-pipe
When sounding it fundamental note
It should be shortened by of its origina 1 length
When sounding its 1st overtone
Foints such as A, B and C, where no particle displacement occurs, are called Nodes, while the points half-way between, where the particles suffers maximum displacement, are called Antinodes.
(1) Distance between
two successive podes:
(iii) an antinode and a neighbouring
avelength
/2
75/4
(11) two successive antinodes
(11)
B; any standing wave formed in a closed tube must be one which places a node at the closed end. The open end absorbs any pressure changes occuring there. It must be a pressure node or a displacement antinode.
a stretched string must be held rigidly at both ends, hence these two points must be nodes.
(111) D; the first overtone is a violine string
is an odd harmonic of three nodes. (iv) C; for open pipes, pressure nodes exist at
both ends. We have displacement antinodes and a node in between them.
(c) (1, ut is at a node as there is no displacemen
of particles.
(11) The distance span of 4 successive nodes is
12
7- 2112 cm.)
3000
Closed pipe
Open pipe
The open pik
higher pitch
·(b), (1).
(11)
The maximum of a sounds with the minimum of
B. The two superimpose and give silence.
1100
Ans. The length of the open pips 18 2 feet,
Questions for next week",
39.(a) Which kind of material, soft iron or steel,
could be used for the following: permanent magnet, electromagnet, magnet keepers, Loudspeaker magnet, telephone earpiece- diaphragm? Give reasons for your answers. Describe two different methods of making magnets, Draw diagrams to show the poles produced and give a rule for predicting the polarity,
(c) Three similar bars are painted the same colour..
One is magnet, another is magnetic but riot a magnet, and the third is non-magnetis. Explain now you would distinguish between the thres bare without given any other apparatus. What are the essential features of the molecular. theory of magnetism? How can the theory be used to explaini
(1) that a specimen of iron cannot be magnetised
beyond saturation point;
(ii) that intense heat destroys magnetism; (iii) the use of soft Iron keepers in storing
pairs of magnets;"
(1) that a magnet cut into two parts produces
two magnets;
(v) that an iron ring can be magnetised so
that ho poles appear.
102000
34000 cm./sec.
340 m./sec.
The velocity of sound is 340 m./sec.
bon
49.2 39.4
0.0203 0.0254
32.8 ·24.6.
0.0305 0.04065
n sec.
256
320
384
512
graph of - against n is plotted as below. It is a straight line.
The intercept of the slope with the co-ordinate at 0.008 cm shows that the length of 1/0,008 cm, gives a note of 100 per
om. = 125 om.
0.008
AAAAA
The true-line wave A superimposes with the dotted-line wave shapes the resultant beat R.
(c) A resonance tube is placed well down in the
water and gradually raised. As this done a vibrating fork is held over the month of the tuba, and when resonance occurs, that is the note of the fork awells out to its loudest volume, the length of the tube above the water level is measured. Three or four values of are found and the mean taken. The tube is now further raised out of the water, and a second position of resonance is found a mean value of the length of the air colum being obtained. The experiment is repeated with other tuning forka
in turn. From the results a moan value for the velocity of sound at the temperature of the Experiment is determined.
A charged ebonite rod repels a polythene rod rubbed with a duster and attracts a rubbed cellulose acetate strip (1) What is the charged on the polythene rod? (11) what is probably the charge on the acetate strip, and how would you make sure of your answer by another experiment? (b) Apparatus used for demonstrations in
electrostatics is often warmed first. Explain | why this is done.
I wood an insulator in electrostatics? Explain
your answer.
A charged rod attracte a suspended piece of cork and then repels it after contact with the rod. Explain why this happens. In what way is this different from the behaviour of a steel pin when a magnet is brought close to it?
(a) In Fig. 1 a deep metal can is placed on the top
of a gold-leaf electroscope. An insulated
positively charged shpare.A touches!
(1) the outside P of the can;
(ii) the Inside Q at the top
Does any charge, remin on A in each case? Giva
reason for your answer,;
The charge & 19 now Lowered deep inside the can, and then touches the bottom 0; Fig. 2, and is withdrawn.
(1) Describe the divergence of the leaf að A
is lowered and then townhas C.
+ Show in a diagram the charges on the
inside and outside of the can before. A touches C, after 1 touches C.
(it) Has any charge left at A after touching C3 Describe how you would verify your answer.