[填空题]
The intensity at the threshold of qzl jr7z;if0u8b 1.fo hearing for the human ear;19gs*cs tvqwpwli e1,u3; yn at a frequency of about 1000 wq n,il;cvgu*sywt193e1;s p Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =
