it just simply says sketch the form of the stationery wave set up in the tube. no mention of only half a wavelength
Ok what do u mean by certain rules?
The tube on the left show an anti node at the top,
To find the NEXT antinode, half a wavelength is drawn,
if we were to draw a complete wavelength instead, 3 anti nodes will result, but they want the NEXT antinode, which is formed by drawing half a wavelength
sorry but i dont know how to explain it more than that,
did that cover ur question?
maybe i didnt fully understand ur que