育教華貞三張七第 日三初月三年戌庚層夏 WAH KIU YAT PO
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「星日八月四年〇七九一公年九十五國民華中
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19. (D) is correct.
僑樂
The wavelength of the fundamental note The wavelength of the firet overtone
The wavelength of the second overtone. Because
constant
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22:
5x150
-750
When it sounds its first overtone, it has two nodes in it. The length of the air column is then equal. to one, wavelength;
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201
(D) is correct.
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物理科:
(#)
21.
(E) is correct.
PHYSICS (23)
Answers and suplana
Gultiple Choice Test on Sound
1. (B) 18 correct.
Sound travels in material media. (D) and (E) are incorrect. It travels fastest in solid.
(3) ia correot,
Velocity of sound is independent of the atmospheric pressure.
(E) is correct.
The range of audible frequency is 20 to 20,000cps.
COTTB0%.
(C) 38 007
One complete vibration is known as one cycle. A repetition of a particle in wave motion is called a cycle.
(4) is correct.
The amplitude of vibration of a wave motion 18 Tas maximum dieplacement of a particle from its mean position.
(D) is correct,
Although the frequendy of the motion is constant
the amplitude of it decreases. This indicates that its intensity is decreasing.
(C) 15 Correi
This is the definition of resonancë.
(A) 18 correct.
Intensity depends on the amplitude of vibration but not on frequency,
(D) is correct.
Beats - difference of two frequencies
512 – 508 - 4 beate
516 - 512 - 4 beata
--18 correct.
508 - 8 beats
When the frequency is one octave higher, the. fro uency should be doubled.
(▲) is correct.
When ▲ sounde with B (440 cps) there are three beate per second. Therefore, the frequency of 4 should either be 443 ops. or 437 ops,
When A sounds with G (442 ops) there are five beats per second. The frequency ofá sould either be '437 of 447 Ope
With the above informations, the grequency of should be 437 cpar
12. (D) is correct.
18.
The column sounde ita fundamental when its length equals to or its wavelength. Therefore the length is one-quarter of its wavelength Because frequency velocity/wavelength Wavelength
330/288
-330/(288 x 4) metres.
28.7 cm.
water column is (100-28.7) 0.
(E) in correct..
Nodes and antinodes occur in all stationary waves.
(D) is correct.
The Laws of vibrating string states that the freq- vency of sound emitted is:
II.
inversely proportional to the length of the vibrating string
inversely rpoportional to the square root of the tension of the string, and III, inversely proportional to the square root of the mase per unit length of the string,
(A) is correct.
Frequency is inversely proportional to the length, and is inversely proportional to wavelength. Therefore, the wavelength is directly proportional to the length of the string,
(B) is correct.
It is the fundamental way
(D) is correct.
The pitch of a sound is determined by its frequency. The higher the pitch, the higher the frequency For a stretched string, frequency is inversely pro- portional to the length of the wire. Therefore, the shortened wire sounda a higher pitch.
(A) is corrects,
The wavelength of the fundamental of the open pape is 2 x 4 feet.
The wavelength of the fundamental or the ca pipe is also 8 feet.
The length of the closed pipe is of it.
22.
Two sound waves which are exactly out of phase, with phase difference 180 degrees, will cancel each other and result in producing silence.
(▲) is correct.
Sound persists in our ears for 1/10 second, whom it travels more than 110 feet, its reflection is"} heard as a separated souid.
The reflecting surface must be 55 feet from the sound source..
(C) 18 correct.
a-red, visible
The sequence of arrangement is (in an increasing frequency) heat, radio waves, spectrum, ultra-violet, X-rays
24. (D) is correct.
Statement I is correct. tromagnetic waves, Statement III is correct. waves.
Statement Vis correct.. can travel in vacauo?
That is, statementa
(D) 18 correct.
Light and X rays are elec-
They are transverse
All electromagnetic waves
III and V are: córract.
The increase in loudness produced by two vibrating bodies is called beats..
(D) ie correct.
Let x be the unknown frequency
X-512-6.
512x..
THE NATURE OF LIGHT
518 506
The study of light dividea naturally into two streame, on the one hand ie that part known as goon- etric optics, which deals with the straight-line pro- pagation of light and the laws of regular reflection and regular refraction.. These lave, which involve atraight lines and angles (geometry), explain the formation of optical images by optical instrumenteï On the other.. hand, physical optica deals with those aspects of light which are more closely related to the nature of light, such as interference, diffraction, and colour. In our ayllabus attention is devoted to geometric optics than to physical optice."
PHOTOMETRY
⠀⠀ To express quantitatively the amount of light. emitted by a point source, we assume that all the light fall on a spherical surface enveloping the sour- co" and the unit amount of light is that amount which emits in a unit solid angle (ster-radian) by a stand- ard source (candle). Such a unit of light flux is known as a lumen.
Intensity of a source.
The lumen ie the amount of light emitted by the a standard candle in a ster-radian, The lumen is a unit of radiant power which is aleo expressible in watts. 685 dumene of green light correspond to one watt.
The modern definition of lumen is defined as 1/685 watts, for green light, and the candel is that in- tensity of a point source capable of emitting one lu- men in one ater-radian.
The number of lumens F emitted by a point source of intensity I is
Η ΑΠΙ
Luminance or Brightness
Whereas a point source has intensity, an extended source has luminance (formerly called brightness). It is expressed in candles per unit area. Another unit of luminance is lambert, which is used for thiffusely reflect ing surfaces. Luminance does not depend upon the angle at which is in viewed.
Illuminance or Intensity or lilumination
Huen ligat incidents upon a surface, the sur- face is said to be illuminated or to have illuminance. The illuminance E is the number of lumens received per unit area.
Ata distance of one foot from a candle source, the illuminance is one lumen par aquare foot, or one foot-candle, In general
COS
where I is the intensity in candles.
dia the distance from source to.
·BUDIMOS
is the angle of incidence of
the light on the surface E is the illuminance in ft-candle
Frotometric Kessurements
The intensity of a point Eource may be compared
to that of a standard source by determining the distan- ce it must be placed from a screen to produce the same illuminaca that the standard source produces at a known distance. Applying the inverse square law for normal incidence:
英文科
Someone who lives nexts to you is
P. father.
2. gardener.
your R. carpenter,
S. hunter. Tneighbour.
(EID)
PARST
RS1
The sick old man was taken to hospital5. an
P. ambulance.
Q. envelope.
an R. ice-box..
S, onion.
umbrella.
SECTION
III. Change the following sentences into opposite voice.
They have finished the game.
His friend told him the news.
3. You did it yesterday.
She was elected "Hiss Hong Kong" by then
5. When will the man be set free?
IV. The following conversation needs punctuation. Fut merks in the brackets.
in the correct punctuation?
DICK
How are you going to spend the evening()
Sam()
SAM
Oh) to the cinema (perhaps (1) ye
done all my work() Have you done your's Dick ()
Yes (all that I am going to do ().
SAM
Can you come with me () then (T
DICK
Example 23-
Certainly) I am always ready to go to
the pictures ()
where the subscripte 1 and 2 refer to the
standard and the unknown source respastivaly
and
4.0
Two, light sources are placed 150 on apart and a Bunsen grease-spot photometer soreen is adjusted to such position on the straight line joining them, that the grease-apot disappearar. The two sources are now inter- changed and it is found that the soreen has to de covad through 30 om to cause the spot to disappear againg What is he ratio of the intensities of the sources?.
If x and y are the respective distance of the two sources from the Bóreen in the first position, they must be y and I respectively in the second position. Therefore, the distance moved through by the screen is
The ratio of the intensities.
[Angveri, The ratio of the
questions for next weak
2.
150 120
30
(글)
2.25
IN 2.25
Two lamps, each of 200 candela, are placed together. 10 ft. above the centre of a table-tennis surface, Calculate the illumination at the centre. If one lamp breaks and is replaced by another of 160 oan- dels, at what distance above the centre must the new lamp be placed to provide the same illumination as before?
A street lamp of 100 Candle power in påsend at a le height of 20 fast above the road. A plane mirror of reflection factor 0.8 is placed 2 feet above the lamp What is the illumination on the road vertically below the leap?
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