物理聲音 DSE、CE 選擇題（第 2 頁）

11.

Graph of wavelength against 1/f: straight line rising, dashed extrapolation to the origin

A loudspeaker is connected to a signal generator to produce sound waves. The frequency $f$ is varied and the corresponding wavelength $\lambda$ is measured. The wavelength is plotted against the reciprocal of the frequency as shown above. Which of the following are correct deductions obtained from the graph ?

(1)The wavelength of the sound is inversely proportional to its frequency.

(2)The slope of the graph is equal to the speed of the sound.

(3)The speed of the sound depends on its frequency

12.

John and Tom communicating with two paper cups connected by a string

John and Tom communicate with each other by using two paper cups connected with a string. Which of the following statements are correct ?

(1)The sound waves transmitted along the string are transverse waves.

(2)The speed of the sound waves along the string is faster than that in the air.

(3)When John whistles a note of

1000

Hz towards the paper cup, Tom will also hear a note of

1000

Hz.

13.

Which of the following phenomena are due to the refraction of waves ?

(1)When water waves enter shallow water from deep water, the spacing between wavefronts decreases.

(2)A swimming pool appears shallower than it actually is.

(3)Mary can hear loud and soft sounds alternately when she walks across in front of two loudspeakers connected to a signal generator.

14.

Flash lamps used by professional photographers can find object distances by using infrared waves so as to adjust the flash output. Which of the following is/are the reason(s) of using infrared waves instead of ultrasonic waves in such flash lamps ?

(1)Speed of infrared waves is much faster than that of ultrasonic waves making the time for finding object distances shorter.

(2)Objects to be photographed will usually emit infrared waves.

(3)The sound produced by ultrasonic waves makes photographers feel annoyed.

15.

The following data show the frequencies and sound intensity levels of some musical notes produced by a piano.

Note	Frequency / Hz	Intensity level / dB
C	256	64
D	288	68
E	320	65
F	341	63

Which of the following statements is/are correct ?

(1)The note F has the lowest pitch.

(2)The note D has the greatest loudness.

(3)The note C played on a guitar will sound differently from the same note produced by the piano.

16.

Which of the following statements about sound waves are correct ?

(1)Sound waves are longitudinal waves.

(2)Sound waves are electromagnetic waves.

(3)Sound waves cannot travel in a vacuum.

17.

Which of the following is a unit of sound intensity level ?

18.

Two musical notes are produced by two different kinds of musical instruments. The two notes have the same pitch but different loudness. Which of the following combinations of notes satisfies the above description ? Note : The settings of the CRO for displaying the notes are identical.

Four pairs of CRO traces labelled A to D

19.

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

20.

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