If a trumpet or a flute is flat, the pipe needs to be shortened in order to increase the pitch of the sound.
Explanation:
Trumpet or flute, a musical equipment that usually works on sound waves concept. It works like an empty pipe with several holes. When blowing air, longitudinal sound waves get generated by different wave frequencies.
If we reduce the length of the pipe; this causes a higher frequency in the pipe. Longer tubes produce low-frequency sound waves that produce deep sound. Therefore, the length of the flute or trumpet should be shortened when it is flat.