Laser harp   

Demonstration effect: by hand in on the clavichord, strike, will hear a corresponding notes of the piano.
Scientific principle: it is a kind of using photosensitive components made of electronic instruments.Jean is arranged several light source, the top of the lower corresponding to arrange a few light sensitive receivers.When no beam keep out its corresponding receiver will produce an electrical signal, this signal after amplification drive the speaker voice.When you toggle on without the clavichord, with the hand, will block light, represents the corresponding notes to the viewer will hear the corresponding notes, have seemed to be in touch with strings of the harp realistic effects.