物理聲音 DSE、CE 選擇題（第 5 頁）

41.

Which of the following can be reflected and diffracted ?

(1)sound waves

(2)infra-red radiation

(3)X-rays

42.

The depth of a lake can be found by the method of echo-sounding. The depth of a short pulse sent vertically down to the bottom of the lake was received after $0.6$ s. Given that the speed of sound in water is $1440\ \mathrm{m\,s^{-1}}$ , the depth of the lake will be

43.

Which of the following are longitudinal waves ?

(1)sound waves transmitted through a solid

(2)sound waves transmitted through water

(3)waves in a vibrating string

44.

Two sources A and B emitting waves towards the mid-point P

Two sound waves of the same frequency are emitted from 2 sources $A$ and $B$ as shown in the diagram. What kind of interference will occur at the mid-point $P$ when the 2 waves generated are (1) in phase; (2) anti-phase ?

	In phase	Anti-phase
	constructive	constructive
	constructive	destructive
	destructive	constructive
	cannot be determined	cannot be determined

45.

An ultrasonic wave is sent from a ship to find the depth of the sea-bed. A signal is received $0.2$ s later. Given that the speed of sound in sea water is $1500\ \mathrm{m\,s^{-1}}$ , what is the depth of the sea-bed ?

46.

Which of the following statements is/are correct ?

(1)Sound waves cannot be diffracted.

(2)A louder sound travels faster in air.

(3)Sound travels faster in water than in air.