物理聲音 DSE、CE 選擇題（第 4 頁）

31.

Which of the following statements about ultrasonics is INCORRECT ?

32.

Which of the following is/are longitudinal waves ?

(1)Ultrasonic transmitted through air.

(2)Infrared transmitted through water.

(3)Gamma rays transmitted through outer space.

33.

Which of the following is an application of ultrasonic in everyday life ?

34.

Oscilloscope traces of musical notes X and Y

The diagrams above show the traces of two musical notes $X$ and $Y$ on an oscilloscope. Which of the following statements is/are true ?

(1)

X

has a higher pitch than

Y

.

(2)The loudness of

X

is greater than that of

Y

.

(3)

X

and

Y

are longitudinal waves.

35.

Two loudspeakers L1 and L2, 3 m apart, each 4 m from the line XY; Q and P are marked on the line XY

In the figure shown, the two loudspeakers $L_1$ and $L_2$ emit sound waves of wavelength $2$ m. The waves emitted are exactly opposite in phase. Which of the following graphs best represents the variation of sound intensity $I$ along the line $XY$ ?

Four graphs A to D of sound intensity I against position along XY

36.

Which of the following statements about sound is/are correct ?

(1)Sound cannot travel through water.

(2)Loudness increases with the amplitude of the sound wave.

(3)Pitch increases with the wavelength of the sound wave.

37.

A bat emits sound waves of frequency $30$ kHz and receives a reflected signal from an obstacle after $0.15$ s. The speed of the sound in air is $340\ \mathrm{m\,s^{-1}}$ . How far is the obstacle away from the bat ?

38.

The wavelength and velocity of a sound in air are $25$ cm and $330\ \mathrm{m\,s^{-1}}$ respectively. When this sound enters a medium, its wavelength becomes $75$ cm. Find the velocity of the sound in the medium.

39.

The range of sound that a boy can hear is from $30$ Hz to $16500$ Hz. If it is given that the speed of sound in air is $330\ \mathrm{m\,s^{-1}}$ , what is the shortest wavelength of sound in air that the boy can hear ?

40.

The wavelength and velocity of a sound in air are $25$ cm and $340\ \mathrm{m\,s^{-1}}$ respectively. When this sound enters a medium, its wavelength becomes $75$ cm. Find the velocity of the sound in the medium.