Abstract: Acoustic-optic effect in the experiment measuring for the speed of light with optical beat is studied based on modification of the light speed apparatus LM2000C. This modification makes frequency shift of the scattered light visible on an oscilloscope. Student can obtain the relationship between frequency shift and the modulated ultrasonic frequency. This help them to get better understanding of acoustic-optic effect and optical beat formation in the experiment measuring for the speed of light with optical beat.

Key words: Acoustic-optic effect, scanning confocal interferometer, optical beat