Problem 11-60.

The frequency of vibration is fixed by the vibrator. By adjusting the weight (to be determined) we tune the tension in the string and hence the velocity and the wavelength. The wavelength determines how many loops are there in the standing wave.

(a) one loop

(b) two loops

(c) five loops

Standing wave is formed by the superposition of two waves traveling in opposite direction (one forward and one backward). As a result, the antinode in the standing wave is vibrating at an amplitude two times as large as the traveling wave. Keep in mind that you are not really gaining anything extra. It is just a redistribution of energy. While the antinodes vibrate more, the nodes do not vibrate at all.