2017年秋九年级物理下册练习（人教版 pdf版）：21.3广播、电视和移动通信

!"#$%#&$23$#"""!!"!"»v%¼¶ª½'¦¾{=¿‹ë#ÀÃ-Á!üÐá6!ü'+݋ÎTæÎýö68Ý$+Ý%',‚T-Âö!ü'X+Ý/'ì"-3z!üA+݋ë¾##("#("ì""X68Ý',-TÒ¾.ŽöÅA!ü'ƒÝTÈýö!üƒ¾Âö!ü'/ÁT–²áÁÂ#!!"$"%À'¦¾{=¿‹ë#01Ò21!üÐù6!ü'‹ë¥Ò6!ü'Xýö68Ý/'¤1ì"‹ë¾##("#ì"("Xýö68Ý',-TÒ¾3ŽöÅA68Ý'ƒÝTƒ¾21!ü'4i67-21!ü4i'51ˆ–²21#!!"%"Á™%§žžŸ6l6À˜—žŸ’"6á!7-SAÁ„Ðùýö6!ü‹ëXZ!´88GX®žŸ"Â¥!9:ZA68Ý!]S("X¤Àß}í¦A!$#!#"#EFG&HIJ:KL56"!"»v%¼¶ª½'¦¾{=¿!#!t2$á÷S4,0z&!f&S4@ïˆ$S4&TkÎ,šw=#"&"$'#ûü"(#‡(Z&#>‡Z)#­®$#ì„i(¼`rˆ¹«,zW!ÎõO*!ºˆzWN„ÕOO½üˆ#¯ˆ$!K¶ºˆzW°º,=#")"$'#Ç2(#x‹Z&#‡(Z)#‡±Z91!à?¯Ø6¸4àí¶(ò—ß0(áâ!Hø¸T[À?b(U!²DYñ¢!à?¯£¤ø(šJtQÀ>šJZ!´V-Z=®6Þ(ò#!"ø{‚a=0(òñŽ!uà?¯ËÌ°e¥?#%#z$!+%+!=D×$Ñ,‹˜ƒ­z!‡z<Rˆ)·ï,=#")"$z$!+%+!'#ˆ$Ñ(#)*$Ñ&#0ˆ$Ñ)#ˆ$Ñ56"$"%À'¦¾{=¿,#zW%$0W%áW\=ôY$͋AwU>S#“F,#-#$0S4ì²zËS43&S4!$0S4@$0ˆØWO$00zW,“FÓ>&!5aDJK,=#"'"$'#&S43zËS4\=`_!$͋¸,(#&S43zËS4\=`_!$Ѹ,&#zËS4=`_!$Ѹ,!&S4=`_!$͋¸,)#&S4=`_!$Ѹ,!zËS4=`_!$͋¸,.#5a.C$0S4Ø,D&!JK,=#")"$'#³ËW=f$S4Q_ðS4(#ûü=f$NQ_&N&#%&Z=f&S4Q_$S4)#ØWØ$͋fS4“0zW91!¦§¯šø˜šJtQ!(šJ"6!šø>¸tQ!(¸"¨>?šø(šJtQ!>šJ"—߯—ß(áâø