[填空题]
The intensity at the threshold on6 8mn*5 x6qboetl mdag.o;v 2f hearing for the0mjyma-zlb2 cpr97- zp;m dy2 human ear at a frequency of ab2b -mzmy-ld y;7rm j0p2zca9pout 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 =
