How does the device work?

        The microphone we are using is the Dynamic microphone, this microphone is an acoustic-to-electric transducer that will convert sound into an electrical signal.

Therefore,when we speak, It induces the current to the op amp,then the op amp will amplify the voltage large enough to turn on the transistor. The transistor acts like a switch, so once it's turned
on by the amplified voltage, the entire circuit would then become a complete
circuit

After that,the current from the 3V power supply wouldthen flow through from collector to emitter and then the laser pointer would bepowered.
        However, the intensity of the laser beam would change based on the loudness, or the amplitude of the sound produced. Italso means when you speak louder, the intensity of the laser beam  should
be larger, and when you speak quieter, the intensity of the laser beam shouldbe smaller

Therefore, different amount of energy would then be transmitted by the laser pointer to the solar panel.When the laser beam reaches the solar panel,which is a semiconductor,the solar panel would absorb the energy,and the energywould  knock off and free the electron on the solar cells
Those freed electrons would then flow andfinally become the current which input the signal to the speaker and allows itto convert the light signal back to the sound signal

The Circuit Diagram