1973-05-24 — Page 19

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罗僑榮

battery. The current in the

HALL

185 A

0.5 A

0.6 A

橋

1913英文中學會考試題預習專欄

緊道英文書院主編

物理科 (卅一)

接第五張第二頁

wire of uniform cross-sec

nd of

2

ional area 10-2 cm2 and

length: 10 cm has a resistivity of 2 ohms/metre. The resist- ance of the wire is

P. 200 ohms.

20

ohms.

10

ohms

105 ohms

T. 0.2 ohms

9. If the wire in Qn. 8 is bent

in the form of a circular loop, what is the equivalent resist- ance between the ends of one. of its diameter?

400 ohms.

40 ohms

100 ohms

10 ohms

cannot be determined because the radius of the loop is unknown.

A metal resistor is connected ac 30ss a cell. If the resist- or is heated,

the current in the circuit decreases.

Q. the potential difference

across the resistor decreases

R. the resistance of the

resistor decreases..

the ir heat dissipation remains constant.

the resistance remains contant.

11. A 160 W, 200 V light bulb.

and a 30 W 200 V light bulb are connected in parallel across a 200 V ac supply the total power consumed is

A. 45 W

B. 90 W 0.30% W

D: 60 W

120 W

12. If the 2 light bulbs in Qn. 11 are connected in series across the same supply, the total power consumed is

20 W

B 40 W

C. 60 W

D. 30 W

D. 1 A

E. 1.1 A

14 If the cells in Qn. 13 are joined in parallel and the. 2 ohm resistance is connected across the cellg, the current in the circuit is

1.2 0.6 A

1 A

E. 0.2

15. An accumulator with a capacity

of 30 Ah means that it would maintain a current of 2 A for

4.30 hrs

B. 15 hrs

C. 60 hrs

D. 120 hrs

E. 150 hrs

16. An ammeter reads 1.8 A.. It is

found that 0.236 gm. of silver. is deposited in 1.00 sec find the error in the ammeter reading.

(1 faraday = 96500 coulombs

and atomic weight of silver is 108 and silver is mono- valent)

P: 0

Q. 0.2 A too large R. 0.2 A, too small 5.0.4 A, too large. 1. 0.4 A, t too small

Find the decrease in mass of the zinc rod in a Daniel cell when 2 gms. of hydrogen is liberated,

(equivalent weight of zinc is

32.5)

P. 32.5 gm. Q.16.25 gm.

12 gm.

65.0 gm.

cannot be calculated because

the e.c.e. of zine is not known.

18. If the cost of electrical

energy is 25 g/kwh. What is the cost of lighting a house with five 60 W lamps continu- ously for 10 hrs?

P 25

Q. 50

R. 60

S: 75 T..100

19. Which is true?

magnetic field is produced

when the current is

I steady

II. decreasing

E. 90 W

3 cells of emf 1 volt and

internal resistance 1 ohm are

joined in series to form a

is connected across the

III. increasing

IV. altemating

I only

Q. I & II only

R. I & III only S. I & IV only

T.All of them

battery. A 2 ohm resistance

四期星

20. A beam of electrons is pro- jected (from left to right)

into a region of space in

日四廿月五年三七九一公年二十六國民華中

which a magnetic field is applies in a vertically upward direction..

The electron beam will be deflected upward..

The electron beam will be deflected downward.

R. The electron beam will be

deflected in a direction pointing out of the paper. The electron be deflected in a direction pointing into the paper.

The electron beam will be accelerated but will not be deflected.

A wire pointing in the E-W direction is dropped from a large altitude. Which of the following is correct?

The induced emf produces a current flowing in the direction from east to west. B. The induced current is from

west to east.

C. The rod becomes magnetised,

the end pointing east being the north pole.

The rod becomes magnetised the end point west the north pole.

E. The rod becomes magnetised and also has an induced current flowing in it

A simple motor has a back emf of 150 V when the voltage

The % of applied is 200 V. energy wasted is

-75%

25%

C. 429%

D. 57%

cannot be determined.

23. A 200 V stop-down mains trans-

former is used for lighting give 12 V, 24W lamps and that the primary current is 1 A the efficiency of the transformer

is

A. 30%

B. 40%

C 50%

D. 60%

E. 80%

24. An ammeter of resistance 5 ohms.

with a full scale deflection of 1A is shunted to measure

The currents up to 10 A. shunt used is

50 ohms

45 ohms:

C.

2 ohms

ohms

G

4

ohms

25. A beam of electrons is emitted

by the cathode. The anode is at a potential, of 400 V higher than that of the cathode. If the mass of the beam is.

9 × 10-15

kg and the total

A

charge of the beam is

16 x 10-5 coulombs. What is

the number of electrons in

the beam if the electron

charge is 1.6 x

1015

B. 10-15 C. 1.6 x 10+5 D. 16 x 105

E. 9 x 10+15

10-19

coulomb.

26. In Qn. 25, what is the K.E. of

the beam reaching the anode?

joules

6.4 x 10- 0.64 x 102 joules

R. 5.76 x

3.6 x

-16.

joules

10712

joules"

cannot be determined because the velocity of the electron beam is not given.

In Qn. 25 what is the anode. current if the electron beam takes

ee to reach the

anode.

16 MA

Q. 16 x 10-7

R.

1017

Which of the following is untrue?

P. I.R. has wavelength greater

than that of visible of light and is detectable by human sense.

A Gamma ray photon is emitted When a nucleus is jumped from an excited state to a more stable state.

R the range of alpha particles

emitted by Amercium-241 can be measured from their cloud chamber tracks.

A beta particle is emitted. when a radioactive nucleus has an excess number of neutrons.

X-rays are produced when highly energetic electrons bombard on a metal target.

When an electron jumps from a higher energy level to a lower energy level,

P. it emits B-ray Q. it emits X-ray

R. it emits a photon S. it emits a proton I. it emits a phonon

30.

P has a longer half-life than Q means that:

P. P has greater mass than Q. Q. P is more energetic than Q. R. P takes more time to decay

completely than Q..

P takes longer time for half of its atoms initially present to decay than Q does

decays quicker than Q.

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