Question

As the length of a vibrating column increases, its frequency "

• A. Decreases
• B. Inceases
• C. Remains the same
• D. Increases if the vibrating column is not in air

Answer 1

The correct option is A Decreases

Answer is A.
The tube of any wind instrument acts as a container for a vibrating air column. The air inside the tube will be set into vibration by a vibrating reed or the vibrations of a musician's lips against a mouthpiece. While the speed of sound waves within the air column is not alterable by the musician. They can only be altered by changes in room temperature and the length of the air column.
For a trombone, the length is altered by pushing the tube outward away from the mouthpiece to lengthen it or pulling it in to shorten it. This causes the length of the air column to be changed, and subsequently changes the wavelength of the waves it produces. And of course, a change in wavelength will result in a change in the frequency. So the natural frequency of a wind instrument such as the trombone is dependent upon the length of the air column of the instrument. Therefore, as the length of a vibrating column increases, its frequency decreases and vice versa.