In which of the following diagrams is the length of the tube equal…
In which of the following diagrams is the length of the tube equal to one wavelength?

QUICK ANSWER…
A
DETAILS…
The simplified illustration is given in the sketch below so that you can quickly and easily solve problems like this in the future:

For any problem featuring tubes with wave lines as shown above, please always note that the length of each half circle = λ/4 = one-fourth of the wavelength.
For this featured sketch, the total length of the tube will be = addition of each λ/4 = λ/4 + λ/4 + λ/4 + λ/4 + λ/4 + λ/4 + λ/4 = 7λ/4
So, L = 7 λ/4
Applying this idea to each option to determine the option with L = λ, we proceed to each option.
Now for the right answer to the above question:
- Option A is correct. L = λ/4 + λ/4 + λ/4 + λ/4 = 4λ/4 = λ
- Option B is incorrect. L = λ/4 + λ/4 = 2 λ/4 = λ/2
- C is incorrect. for tube C, L = λ/4
- D is not the correct answer. for this option, L = λ/4 + λ/4 + λ/4 + λ/4 + λ/4 = 5 λ/4
KEY-POINTS…
You may please note these/this:
- The length of each half cycle = λ/4.
- The length of any kind of tube can be resolved by dividing the wave lines into half cycles and adding each individual unit as λ/4.
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/ culled from 2020 JAMB-UTME physics past question 38 /