निम्नलिखित में से कौन-सा ध्वनि तरंग की मूल विशेषता/गुण (जैसे आवृत्ति या आयाम) होने के बजाय अनुदैर्ध्य तरंगों से जुड़ी एक संरचनात्मक घटना है?

The second overtone of an open organ pipe has the same frequency as the first overtone of a closed organ pipe of length L. The length of the open pipe will be:

A siren on a tall pole radiates sound waves uniformly in all directions. At a distance of 15 m from the siren, the sound intensity is 0.250 W/m2. The intensity of sound at a distance of 75 m from the siren is: