1968-05-15 — Page 23

-15 MAY 1968

莫三弟强六第

日九十月四年申戉壓夏

WAH KIU YAT PO

0968

CITY HALL

日五十月五年八六九一联公年七十五國民事中

英文中學會考試題預習專欄

The first reflection is at the convex mirror.

object distanze ul

- 20 cm.

300.

AC2

物理 科

(廿九) ·陸永爟·

Focal length of the convex mirror_• 5))}

10 cm.

300

(t. candle

Image distanceiv

302

The illumination at C due to`lamp 8.

-

Physics (29)

300

20

000 0.

5. Solution

CBX

20

Γ 300

[AC]

CB2

CB

(a) i) Characteristics of Images formed by s ̄plans] ·

4

mirror*:-

(1) Image position. The image is as far

behind the mirror as the object is in front.

(2 It is erect relative to the object."andi

le the same size,

(3. Lateral inversion.

(4

It is virtual. No light energy rea ches) the region behind the mirror, so the image cannot be formed on a screen,

The principal focus of a conarve mirror is the point on the principal axis through which all rays originally parallel to the. azia sasa after reflection.

(b) Determins tion of the focal Innotb of a concaveĮ

mirror.

ans. The first image is, wherefore, a virtua

one,16 cm,behind_the_mirror?,

İyne`second"reflection is at the conca veļ mirror. The virtual image of the convex mirror constitutes the object.j

object distance,• 42**

[Focal length ̋á

(4+ 62)-ema

462 cm 1

The concave mirror 20 cm) Image_distance...”.

300 x 30

√302440232

9000

50

ft candle

Total illumination at C due to both lambe

2

300 302

9000

503

*0.333 +0.073 (-10.405 ft. candle

/8)

Focus eye on) object pin

2

3

20

12

[Ans. The second image is geal and is formed

"at a distance of 1219. cm in front of

the concave mirror.

7. Tal fuman eve and Vémera

D

11) Illumination"at"D"due_to_each_lamp]

300

08

object "aving\

The concave mirror is susported vortiMLIJ in a mirror-holder. An optical pin, stucked i a cork, is adjusted so that the tip of the pin / Lies on the principal axis of the mirror, The pin is then moved along the bench in front of the ndrror until a real inverted image of the pin is then moved to and fro until there is no paralia, between the oin and its image. The distance between the mirror front and the optical sin is measured which is the radius

of turvature of the mirror, Its focal length is) half of this value.

Human Eye

A light-tight box

back A film at the

"An aperture varies the ime of exposure and thus the amount of

energy incident

A geommodation is made by means of moving the lena. towards or away from the film,

Permanant image is developed by chemicals on the "negative",

Camera

A light-tight Retina lined setisory cellar

Lerotic

The size of the pupil adjusted the "rådial" and "ring" muscles of the iris regulates the incident light.

Accommodation is

possible as: the curva turej of lens varies

automatically on seeing, near and distant objects,

The brain interpreta Sensation into a temporary image.

300 &D,

OR

300 x 30

1333

9000

46870

- 192

+ 20733

Illumination due to both lamps,

- 0.197 x ?

1. 0.384rt-candles;

the given ortam. mpressanta cha Dash of

the say thr

the prsand F. Being the point of tatal

Legion

2

horam is a G and 'inconsmet al d..

The animum angle of emergenas LNÍ MÍ given by the minimum angle of total reflection at f. It la, unmreforg, täm

Fince JPCG to concyelis, in

FG 1200"

+420- 180

et ton at

· 60

glese tole

HONG

11) Short-sight

This is due to:-

(a) eyeball" too long, or

(b) over-fatigue of ciliary muscles so that the lens in its resting state have a focal length less than the distance to the retina. Image of distant objects are formed nearer to the lans than the retina, A short sighted eye usually has its - nearest point of distinct vision at distance of less than 10 inches.

It de corrected by using spectacles with concave lenses. These make raya from objects more divergent before entering the sye, so that image formed by the eye lana i further back than when the spectacles are absent..

8. Sölution given "next"week")

Questions—for next week-

RE

Đen aribe the action of a simple ̈ce LL, Zhenics)

explain the terms:

polarization

(1)

(11)

111)

local action

E.M.F. of a cou

(b) (1) State Ohm's Law,

(11) Describe, and explain briefly, with the help of labelled diagrams, how to use a voltmeter and an ammeter to meBSUPE (1) a very high resistance

(2) a very low resistance

(e) Each cell in the circuit has an 8,n,t,” of

KONG PERIC LIBRAY

2 volts and an internal resistance of 1 ohm, (1) Find the currant through the lamp.

(11) The heat produced in thế 20 ohms resistor in'

one hour.

A

(111) The mass of copper dañosited on the ›

cathode of the copser voltameter in 30 min.) The internal resistance of the voltameter La 5 ohms,

ه طریقه تم

(electrochemical equivalent of copper.

- 0.00033 cm /coul, ),

Errefors

1.5 sintàco.

telescope

Lana

An electrio: wätte.

-FIT:

3 ce Lia)

'20 n

ID 2

rked

...! fööni "length of object lens,

*.g. starTRY

are sensibly

(1) What does this meaḥ? 1) Calcul to the resistance

(114) Calculatesthe cost of eléctri

$0,3: net Thit; af 2 of these

in series, are swibo

.connected, to a

of

Copper Volta-

The ter