2. The figure shows an experimental set-up for the demonstration of the speed of sound. The electronic stop-clock can be turned on when microphone X receives a sound and it can then be turned off when microphone Y receives the same sound. The distance between X and Y is 5 m. A student claps his hands just next to X and the electronic clock records a time interval of 0.015 s. The speed of sound determined by the experiment is

2. 圖中展示了用於展示聲音速度的實驗設置。當麥克風 X 收到聲音時，電子秒表可以開啟，然後當麥克風 Y 收到相同聲音時可以關閉。X 和 Y 之間的距離為 5 米。一名學生在 X 旁邊拍手，電子時鐘記錄了一個時間間隔為 0.015 秒。由實驗確定的聲音速度是

3. 3. A thunder is heard 1.5 s after a lightning is seen. What is the distance between the observer and the place where the lightning occurs?

4. 3. 一道閃電被看見後 1.5 秒後聽到了一次雷聲。觀察者和閃電發生地點之間的距離是多少？

A boy measures the speed of sound of air. Initially he is at position P in front of a cliff. He shouts loudly and at the same time he starts his stop-watch. He stops his stop-watch once he hears the echo from the cliff. The time interval measured is 0.6 s. He then walks away from the cliff for a distance of 70 m to position Q and repeats the above procedure. The time interval measured this time is 1.0 s.

4. 4. What is the speed of sound measured by the boy?

5. 一名男孩測量了空氣中聲音的速度。起初，他站在懸崖前的位置 P。他大聲喊叫的同時啟動碼錶。一旦聽到懸崖回聲，他停止碼錶。所測得的時間間隔為 0.6 秒。然後，他從懸崖向遠處行走 70 米 到位置 Q，並重複上述程序。這次測得的時間間隔為 1.0 秒。

6. 4. 請問這位男孩測量到的聲音速度是多少？

4. A boy measures the speed of sound of air. Initially he is at position P in front of a cliff. He shouts loudly and at the same time he starts his stop-watch. He stops his stop-watch once he hears the echo from the cliff. The time interval measured is 0.6 s. He then walks away from the cliff for a distance of 70 m to position Q and repeats the above procedure. The time interval measured this time is 1.0 s.

5. 5. What is the distance between the cliff and position P?

6. 一名男孩測量了空氣中聲音的速度。起初，他站在懸崖前的位置 P。他大聲喊叫的同時啟動碼錶。一旦聽到懸崖回聲，他停止碼錶。所測得的時間間隔為 0.6 秒。然後，他從懸崖向遠處行走 70 米 到位置 Q，並重複上述程序。這次測得的時間間隔為 1.0 秒。

7. 5. 求位置P與懸崖的距離。

6. 6. We can hear the voice of a person behind an obstacle but we cannot see the person. Which of the following statements best explains the phenomenon?

7. 6. 我們能聽到一個人在障礙物後面的聲音，但看不到這個人。以下哪個描述最好地解釋了這種現象？

7. 7. Sound wave can undergo diffraction more easily than light wave because

8. 聲波較光波易進行繞射，原因是

8. 8. Which of the following statements concerning the diffraction of sound wave are incorrect?

9. (1) Loud sound diffracts more than soft sound

10. (2) High pitch sound diffracts more than low pitch sound.

11. (3) Sound wave diffracts more than electromagnetic wave.

12. 以下有關聲波繞射的敘述中，哪些是不正確的？

（1）強聲的聲音比較容易繞射，弱聲的聲音則不容易。

（2）高音的聲音比低音的聲音容易繞射。

（3）聲波比電磁波更容易繞射。

9. 9. Which of the following adjustments can increase the separation between positions of loud and soft sound the most?

10. 以下哪項調整最能增加強聲與弱聲訊號間的距離

10. 10. Which of the following statements correctly tells a difference between a sound wave and a light wave? 以下哪項能說明聲波及光波的分別？

11. 11. If the speeds of light in air, medium X and medium Y are 3*10⁸ms^-1, 2.5*10⁸ms^-1 and 2.0*10⁸ms^-1 respectively, which of the following statements about the refractive indexes of these media are correct?

12. (1) the refractive index of X is 1.2

13. (2) the refractive index of Y is 1.5

14. (3) the refractive index when light travels from X to Y is 1.25.

15. 如果光在空氣、在介質X和介質Y的速率分別是3*10⁸ms^-1, 2.5*10⁸ms^-1 及 2.0*10⁸ms^-1 ，下列有關些介質的折射率的敍述，哪些是正確的？

16. (1) X的折射率是1.2

17. (2) Y的折射率是1.5

18. (3) 當光從X進入Y時，折射率是1.25

12. 12. If $$\theta$$ _c is the critical angle of a medium, v is the speed of light in the medium and c is the speed of light in air, which of the following equations is correct?

13. 如果 $$\theta$$ _c是某介質的臨界角，v是光在這介質的速率，c是光在空氣的速率，下列哪條方程式是正確的？

13. 13. If the speed of light in a medium is 1.8*10⁸ms^-1, what is the critical angle of the medium?

14. 如果光在某介質的速率是1.8*10⁸ms^-1,這介質的臨界角是多少？

14. Two loudspeakers are facing each other at opposite ends of a room with a distance of 15 m in between. They are in phase and emit notes having the same frequency of 68Hz.

15. 14. How many points are there between X and Y (maximum) signal? (You may neglect the positions at the loudspeakers.)

16. 兩個面向對方的揚聲器分位於房間的兩端，揚聲器之間的距離為15m。它們發出的樂音是同相的，而且頻率為68Hz。

17. 14. 在X和Y之有多少點可探測到響(強度最高)的訊號？(不須考慮揚聲器所在的位置)

14. Two loudspeakers are facing each other at opposite ends of a room with a distance of 15 m in between. They are in phase and emit notes having the same frequency of 68Hz.

15. At which of the following positions, between X and Y, could a detector be placed and receive a weak (minimum) signal?

16. 兩個面向對方的揚聲器分位於房間的兩端，揚聲器之間的距離為15m。它們發出的樂音是同相的，而且頻率為68Hz。

17. 15. 在X和Y之間，下列哪位置可探測到弱(強度最低)的訊號？

18. (1) 1.25 m from X. 離X點1.25m的位置。

19. (2) 3.75m from X. 離X點3.75m的位置。

20. (3) 6.25m from X. 離X點6.25m的位置。