Keep trying until you find the correct answer.

1. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
   

   1.   ?    0
   2.   ?    ¹/₄λ
   3.   ?    ¹/₂λ
   4.   ?    ³/₄λ

2. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
   

   1.   ?    0
   2.   ?    ¹/₄λ
   3.   ?    ¹/₂λ
   4.   ?    ³/₄λ

3. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
   

   1.   ?    0
   2.   ?    ¹/₄λ
   3.   ?    ¹/₂λ
   4.   ?    ³/₄λ

4. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
   

   1.   ?    0
   2.   ?    ¹/₄λ
   3.   ?    ¹/₂λ
   4.   ?    ³/₄λ

5. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
   

   1.   ?    0
   2.   ?    ¹/₄λ
   3.   ?    ¹/₂λ
   4.   ?    ³/₄λ

6. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
   

   1.   ?    0
   2.   ?    ¹/₄λ
   3.   ?    ¹/₂λ
   4.   ?    ³/₄λ

7. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
   

   1.   ?    0
   2.   ?    ¹/₄λ
   3.   ?    ¹/₂λ
   4.   ?    ³/₄λ

8. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
   

   1.   ?    0
   2.   ?    ¹/₄λ
   3.   ?    ¹/₂λ
   4.   ?    ³/₄λ

9. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
   

   1.   ?    0
   2.   ?    ¹/₄λ
   3.   ?    ¹/₂λ
   4.   ?    ³/₄λ

10. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

11. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

12. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

13. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

14. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

15. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

16. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

17. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

18. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

19. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

20. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

21. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

22. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

23. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

24. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

25. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

26. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

27. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

28. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

29. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

30. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

31. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

32. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

33. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

34. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

35. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

36. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

37. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

38. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

39. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

40. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

41. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

42. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

43. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

44. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

45. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

46. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

47. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

48. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

49. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

50. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

51. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

52. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

53. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

54. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

55. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

56. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

57. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

58. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

59. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

60. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

61. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

62. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

63. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

64. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

65. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

66. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

67. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

68. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

69. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

70. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

71. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

72. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

73. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

74. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

75. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

76. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

77. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

78. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

79. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ

80. Consider the two loudspeakers in the diagram below. The loudspeakers, shown at t = 0, are playing sound of the same frequency. How far do you have to move the bottom speaker to the right (→) to get constructive interference?
    

    1.   ?    0
    2.   ?    ¹/₄λ
    3.   ?    ¹/₂λ
    4.   ?    ³/₄λ