[填空题]
The intensity at the threshold of hearing for the human ea .8g/qy(-8n,o jx ox /7kiskojhmr1fk r ajhmdui2 +(3;t a1 t7cjnhqrx2 t a frequency of about n+(c hjtu rdtqij7 3xh;212am 1000 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 =
