物理 2003 年 DSE、CE 選擇題（第 3 頁）

21.

Questions 25 and 26 : A transverse wave travels along a string with a speed of $1.2\ \mathrm{m\,s^{-1}}$ . The diagram below shows the shape of the string at a certain instant.

Displacement (cm) against distance (cm) graph of a wave moving to the right, amplitude 3 cm, wavelength 20 cm

Which of the following statements about the transverse wave are correct ?

(1)Its wavelength is

20

cm.

(2)Its frequency is

6

Hz.

(3)Its amplitude is

6

cm.

22.

Questions 25 and 26 : A transverse wave travels along a string with a speed of $1.2\ \mathrm{m\,s^{-1}}$ . The diagram below shows the shape of the string at a certain instant.

Which of the following diagrams shows the shape of the string at a quarter of a period later ?

Four displacement-distance graphs A to D

23.

Plane water waves travelling to the right towards an L-shaped barrier

Plane water waves travels towards an L-shaped barrier in a ripple tank as shown above. Which of the following diagrams best shows the reflected wave pattern ?

Four diagrams A to D of reflected wave patterns at an L-shaped barrier

24.

Plane waves moving from a deep region towards a narrow gap in an obstacle with a shallow region beyond

Plane water waves travel from a deep region to a shallow region of water through a narrow gap as shown above. Which of the following properties of the waves remains unchanged ?

25.

A ringing electric bell is placed inside a glass jar as shown. As air is pumped out of the jar, the sound will die away. Which of the following can explain this phenomenon ?

Electric bell inside a glass jar connected to a power supply and a vacuum pump

26.

Photograph of a digital video camera recorder

The photograph shows a digital video camera recorder. The recorder has a night-shot function of capturing images in the dark. Which of the following electromagnetic waves is employed by the recorder in capturing images in the dark ?

27.

Four point charges at the vertices of a square (+ top-left, - top-right, - bottom-left, + bottom-right) with point charge C at the centre

Four point charges of equal magnitude are placed at the four vertices of a square. The signs of the charges are as shown. A point charge $C$ is placed at the centre of the square. What will be the direction of the resultant electrostatic force, if any, acting on $C$ ?

28.

A square loop $PQRS$ is made of uniform resistance wire. Let $X$ , $Y$ and $Z$ be the equivalent resistance of the loop when connected as shown below :

Table of three ways of connecting a square loop PQRS, with equivalent resistances X, Y and Z

Which of the following relations is correct ?

29.

Figure (a): circuit with cell, ammeter, resistance wire, variable resistor and voltmeter. Figure (b): straight V against I graph

Figure (a) shows a circuit used to investigate how the voltage $V$ across a resistance wire varies with the current $I$ through the wire. The result is shown in Figure (b). If the experiment is repeated using a thinner wire of the same material and of equal length, which of the following graphs (denoted by the dashed line) represents the expected result ?

Four V against I graphs A to D, each with a solid line and a dashed line

30.

12 V battery connected in parallel to bulbs P, Q and R

Three light bulbs $P$ , $Q$ and $R$ of ratings ' $24$ V, $80$ W', ' $12$ V, $80$ W' and ' $12$ V, $40$ W' are connected in parallel to a $12$ V battery. Which of the bulbs will be the brightest, and which will be the dimmest ?

	The brightest	The dimmest
	$P$	$Q$
	$P$	$R$
	$Q$	$P$
	$Q$	$R$