解 = (1)在空气中 V= 20HZ 340 =2 0 =17m 340 V=2000Hz =2×104=17×103m (2)在水中 V= 20HZ 2、1450 20=725m =2×104Hz2_1450 目录 20=72.5×103m20 =17m 340 l = n = 2000Hz n = 20Hz 340 l = 2×104 =17×10-3 m n = 20Hz 20 =72.5m 1450 l = n = 2×104 Hz 20 =72.5×10-3 m 1450 l = u n 解： l = (1)在空气中 (2)在水中 目录