1969-06-03 — Page 15

育教傋 真三第張四第 日九十月四年香已滕 WAH KIU YAT PEONY

報日橋式

CITY HALL

明星

日三月六年九六九一曆公年八十五國民華中

He as on:

(接第四張第二页):

英中會考物理科答案

(牆) *陸永熾·

when

Relation between object distance. distance and the focal length

i mà ce

(1) the inverse-square Law of Illumination

The

Lumination of a surface by a point.

source is inversely proportional to the distance from the source.

E is the intensity of illumination

is the luminous intensity dis the distance from the source.

Luminous intensity, b 40

c.p Distance from the source, d; -2. £t. therefore

the

tensity of allumination le

An impu Lae, of compression at the mouth presses the air molecules down: the. tube. Simultaneously, a reflection of an impulse of rarefaction goes up to the the mouth..

whe resu

the object distence vis the mage distance

f the focal length of theirs

All distances are measure and

centre.. Distances of read real cages are positive.

tne optica

Distances ol

virtual objects and images are negative. The focal lengths of converging lenses are real and, be positive."

The focal lengths of diverging leases far

cual and by neatly

10 tt-cand te

Replacing the white screen by a black screen, much of the light energy 19 absorbed and diffused. Illumination Is much reduced.

iv) A perfect reflecting mirror will reinforce

the intensity of al lumina taun. on

Despite a one vertical or horizontat position of the tuning fork, sound waves. are emitted spherically. Resonance does occur in any of the two positions Livey,

(V) Actually the antinode of the fundamentat

of the stationary wave is somewhere up the mouth of the tube, The distance of this antinode from the moù this determined. by the diameter of the tube and is called the..'ead-corretion

2/4 - (l+ c)

linear magnificatio

the height of the images

The the Tgi

the abject and is usually denoted by

image size

object size

the

lowing di

found that

ABAC USI BĽ

IB VA

IC

ELTE)-A TRỳ diagram of an assrun'amical

Vitrinity

virtual

image al

distant object

illumination due to the 40-ev.

source

illumination due to the mirr

10/9.

total ilumination

fe-candle

The

The light source is on the centre of curvature of the concave mirror. image of this source due to the conca mirror is also on the centre of curvature

Ine Lota.i viiùmination

nerezore

0.9 x 40

ft candle

via the velocity of sound fis the frequency

2 is the wavelength

e la. the end-correction.

When a vártage of a.c. supply 18 ACTOAS the sonometer wire, 8 suitable value of wire length AB and tension T is adjusted, A maximum amplitude of vibration indicates a full resonance is obtained. Another position of A and B is readjusted and also the tension of the wire, and the appropriately that of the manets, ko obtain another reïonundelofy the wire. This id done for several values of AB and Finally, the mass of per unit lenztli of the wire is found.

(a) The direction of ground wave in the cube

during resonance

Compress? DA

Bærafaction

OBJECT LENS

common

focal l

EYE LEN

reflectea

Ef given, en h reflected

As the prang ́ex a vibrating FALKEMİZ Tork moves downwards through half s vibration, it sends a pulse of compression down the tube which is reflected on reaching the water eurface, back to the month of the tube.

At the moment she" compression renTDM'S. the top, the prong has just reached the lovest posi ta on, and starte moving upwards It will now send a rarefaction down the tube This, rarefaction will also be reflected to the top at same time". as the

completes a vibration.

ther

At this stage the prong has made oar complete vibration and has sent aut bäs

of sound.. The sound

completed up and down the

wave has twice Lube.

That is, the length of the atr column is one-quarter of a waveletsih.

ASTRONOMICAL

TELESCO

It is difficult to repre- sent the longitudinal tranave THO wave disgraus matically, it is custom- ary to represent it by transverse waxe en rva nashwona

overlapping pools

of light projected

on a white screen

from 3 projectors

(by)

overlapping.

sheete

of coloured glass seen against a white blackground

BLUE

GREEN

A

BLUE

GILLEN

C

RED

RED

D

WHITE

BLACK

(iv) Velocity of sound.

and

where is, the absolute temperature.

there

Le T

In notter rooms, the resonance leng gumag of the air column should be longer in order to have a resonance. It is pro- portional to the square-root of the abɛom. lute temperature of the room.

A-C. Sup

graph of IT agarast £ is plotted. ratio of FT/l is obtained,

Mai

frequency'

frequency of the resonant wire

-2121.5

980 XY OY

where M 18 mass per unit langth

of the wire

is the acceleration

due to gravity.

Tis the tensionor vire

is the length of wire

(c)

Velocity of sound Velocity of wind

750 m.p.h.

Time taken for sound to reach B

750... 50

3600

800

Time Laken to reflect back to a

750 3600 .700

50

Bec.

"Potare time taken

3600/100 x (~ + =)

36 x 15

56

9.65 sec

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再四第四第日九十月四年司機 WAH KIU YAT PO