As the air temperature increases, the fundamental frequency of the organ pipe in Balboa Park's outdoor organ (a) increases due to the corresponding rise in the speed of sound. So the option A is correct.
The fundamental frequency of an organ pipe in Balboa Park's outdoor organ is influenced by the speed of sound in the surrounding air, which, in turn, is affected by temperature. As the air temperature increases, the speed of sound generally also increases. The fundamental frequency (f) of a closed-end organ pipe is inversely proportional to the speed of sound in the air, according to the formula
where \(v\) is the speed of sound, and \(L\) is the length of the pipe.
With an increase in temperature causing a rise in the speed of sound (v), the fundamental frequency (f) of the organ pipe will consequently increase. This change occurs because sound waves travel more quickly through warmer air. Therefore, the option "a. increases" accurately describes the relationship between air temperature and the fundamental frequency of the organ pipe in Balboa Park. Understanding the physics behind sound propagation in different environmental conditions helps explain how temperature variations impact the acoustic properties of musical instruments like the outdoor organ, enhancing our comprehension of the interplay between atmospheric factors and musical performance.