物理 1996 年 DSE、CE 選擇題（第 3 頁）

21.

Figure (a): shape of string with wavelength x. Figure (b): displacement-time graph of a particle with period y

A vibrator generates a wave on a string. Figure (a) shows the shape of the string at a certain instant. Figure (b) shows the variation of the displacement of a certain particle on the string with time. Which of the following expressions represents the speed of the travelling wave ?

22.

Figure (a): vibrator dipping into a ripple tank of water. Figure (b): plane wave pattern from the vibrator

A vibrator generates continuous plane waves in a ripple tank (see Figure (a)). Figure (b) shows the wave pattern observed.

Figure (c): the ripple tank tilted so the water depth varies

Now the ripple tank is tilted as shown in Figure (c). Which of the following diagrams best shows the wave pattern observed ?

Four wave patterns A to D with different wavefront spacings

23.

Part of the electromagnetic spectrum: X-rays, P, visible light, Q, microwaves

Part of the electromagnetic spectrum is shown above. Which of the following statements is/are correct ?

(1)

P

is ultra-violet and

Q

is infra-red.

(2)The wavelength of

P

is shorter than that of

Q

.

(3)The speed of

P

in vacuum is higher than that of

Q

.

24.

Battery with 6 ohm resistor and ammeter A1 in series with 4 ohm resistor in parallel with 6 ohm resistor and ammeter A2

In the circuit shown, the reading of ammeter $A_2$ is $0.3$ A. Find the reading of ammeter $A_1$ .

25.

Which of the following is **not** an application of the corresponding electromagnetic wave ?

	Electromagnetic wave	Application
	Ultra-violet	Camera autofocusing
	Infra-red	Detecting survivors buried in landslides
	Microwaves	Satellite communication
	X-rays	Detecting weapons hidden in suitcases

26.

A small conducting sphere is suspended by an insulated thread. When a positively charged rod is brought near the sphere, the sphere is attracted as shown. Which of the following is/are reasonable deduction(s) ?

(1)The sphere may carry a positive charge.

(2)The sphere may carry a negative charge.

(3)The sphere may be neutral.

Suspended sphere attracted towards a positively charged rod

27.

It is known that the resistance of a resistor $R$ is about $5\ \mathrm{k}\Omega$ . Which of the following circuits is most suitable for measuring the resistance of $R$ ? The ammeter and voltmeter used are common moving coil meters.

Four circuits A to D with a battery, resistor R, ammeter and voltmeter connected in different ways

28.

Which of the following devices is not an application of electromagnetic induction ?

29.

Figure (a): battery, ammeter and two resistors R in series. Figure (b): battery, ammeter and two resistors R in parallel

In Figure (a), the ammeter reading and the total power dissipated in the two identical resistors are $I$ and $P$ respectively. The resistors are rearranged as shown in Figure (b). Find the ammeter reading and the total power dissipated in the two resistors.

	Ammeter reading	Total power dissipated
	$2I$	$2P$
	$2I$	$4P$
	$4I$	$2P$
	$4I$	$4P$

30.

Iron connected to a 200 V a.c. supply with the switch S and fuse in the neutral wire

The switch $S$ and the fuse of an iron are incorrectly fitted in the neutral wire as shown above. Which of the following statements is correct ?