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                                                  27    When you chat with your friend on a computer, you
                                                     send electronic messages across wires and radio waves, just

                                                     like the old telegraph machines did. Edison began working
                                                     as a telegraph operator in his teens.




































                                                  29    Today we use radio waves to transmit all types of
                                                     signals, including those from mobile phones, radar,
                                                     television, and radio.



                                                          radar  Radar is a way to find unseen objects by using radio signals.



















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