物理 2004 年 DSE、CE 選擇題（第 3 頁）

21.

The solid curve in the diagram shows a transverse wave at a certain instant. After $0.05$ s, the wave has travelled a distance of $2$ cm and is indicated by the dashed curve. Find the wavelength and frequency of the wave.

Solid and dashed transverse waves on a grid of vertical lines, shifted by 2 cm

	Wavelength / cm	Frequency / Hz
	8	2.5
	8	5
	16	2.5
	16	5

22.

$Ripple tank with a vibrator, plane waves, and an obstacle with a gap producing diffracted waves$

A student uses the above set-up to study the diffraction of water waves. Which of the following changes can make the diffraction effect more significant ?

(1)reducing the width of the gap between the obstacles

(2)increasing the frequency of the vibrator

(3)adding more water to the ripple tank

23.

A ship is equipped with certain devices. Which device is **not** an application of electromagnetic waves ?

24.

Two dippers S1 and S2 with dashed lines to a point P in a ripple tank

Two dippers $S_1$ and $S_2$ are connected to the same vibrator and produce identical waves in a ripple tank. $P$ is a point such that $S_1P-S_2P=\lambda$ , where $\lambda$ is the wavelength of the water waves generated. Which of the following statements is/are correct ?

(1)Constructive interference occurs at

P

.

(2)A crest is always formed at

P

.

(3)If the wavelength of the waves generated by the dippers is doubled, destructive interference will occur at

P

.

25.

Which of the following descriptions about microwaves and ultrasonic waves is correct ?

26.

Three conducting spheres are suspended by separate nylon threads. When any two of them are brought near each other, they attract each other. Which of the following deductions is correct ?

27.

Rechargeable cell labelled Standard charge 16 hours at 190 mA, Fast charge 5 hours at 475 mA

The photograph shows a rechargeable cell. If the cell is charged for $16$ hours using the standard charge mode, estimate the total amount of charge flowed through the charging circuit.

28.

An ammeter with negligible resistance and a high-resistance voltmeter are connected into a circuit as shown. Find the ammeter and voltmeter readings.

6 V battery with three 2 ohm resistors in series, a voltmeter across the first and an ammeter across the last two

	Ammeter reading / A	Voltmeter reading / V
	$0$	$2$
	$1$	$2$
	$3$	$2$
	$3$	$6$

29.

David wants to design a battery-powered toy car. Which of the following circuits should he use ?

Four circuits A to D with a motor and switch: A battery, B a.c. source, C battery with the switch in parallel with the motor, D a.c. source with the switch in parallel with the motor

30.

6 V battery, ammeter and rheostat with sliding contact X on AB

An ammeter and a rheostat of range $0-40\ \Omega$ are connected to a $6$ V battery. The sliding contact is located at a position $X$ where $AX=\frac{1}{4}AB$ as shown above. Find the ammeter reading.