[填空题]
The intensity at the threshold of hearing for the human ear *l)j-sq srg.+w y:(8 i a nrq6aomqw5qr fr;ppi+ e -5a5)lj -y )ocjxnmwrr./at a frequency of about 1000 Hz + p5cf)wye-r5 ir.mprrnjx/a;o-j )l 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 =
