Usually, the longer the tube, the lower the note. The three valves of the trumpet add lengths of tubing to the instrument to decrease the pitch. The first valve lowers it by a whole tone, then the second by a semitone, and the third by a minor third. For example, the valves are shown here in order to play the notes of the scale.
The first valve extends the trumpet’s tube by 160 mm, the second by 70 mm, and lastly the third by 270 mm. These measurements are just the right distance for changing the pitch by the expected interval. When the trumpet valve is raised, the air goes directly through, and when it is lowered, a different airway is opened which attaches a section of tubing. The distance to add for the three valve intervals is found by using the known information that the frequency of an air column is inversely proportional to