[填空题]
The intensity at the thret-d b 2zzh,h1psholga q 3dk3a;vi bk1a7vy+.1 c5 zz mhjwq9t4t+fd of hearing for the human ear at a frequency of about 1000 Hz v 9q b4wya . 1+1f3qz5t mav;k+3ktjz7iahgcdis $I_0$ = $1 \times10^{12 } W / m^2$ 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 =
