In this paper we have reported a simple and cost effective lab level experiment to determine the revolution of DC motor at various voltages.This experiment is designed on the basis of laser light pulses observed in cathode ray oscilloscope（CRO）output through an aperture.These output waveforms are directly related with the revolution of DC motor.A laser light beam was allowed to pass through a slot attached with the shaft of DC motor.The outcoming light is in the form of light pulses that falls on the photodetector which was connected to CRO.The frequency of light pulses is the function of applied voltage to DC motor.The CRO output was measured at different voltages.The visual waveforms on CRO interpret the different values of revolutions per minute（rpm）at different values of voltages given to DC motor.Analysis was made to determine the voltage depended revolution.
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