In AM modulation how is an electrical signal mixed with the carrier wave?
In AM modulation how is an electrical signal mixed with the carrier
  wave?


For AM the usual way is to use analogue multiplication i.e. the two signals are fed to a multiplier. The output consists of sum and difference signals i.e. you get sidebands. There is no longer any baseband (well there is no intention but a little will leak through): -



Picture taken from here

You get sum and difference frequencies because that is what happens when you multiply sin a with sin b: -