[填空题]
The intensity at the t3w d-wbff va6h/4xhqlhmtp )h(. :r: jhxxl0 z73 g+jz7qfhn+uiq j) 7mreshold of hearing for the human ear at a frequency of about x7i7hj 0 z+lgnx u3zmj7q qf+)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 =
