解： = U V (1)在空气中 V=20Hz 340 20 =17m 340 V=2000Hz 2×104=17×10-3m 2)在水中 1= 1450 V=20Hz 20 -72.5m 1450 目录 V=2×104Hz2= 20 =72.5×10-3m 20 =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