Physics Lab Equipment

LEOI-24 Apparatus for Measuring Speed of Light

LEOI-24 Apparatus for Measuring Speed of Light

Note: oscilloscope not included 


  • Compact design

  • Phase method with high accuracy

  • Refractive index measurement

  • Optional media tube


This experimental system is designed to measure the speed of light in air/media using the well-known phase method. It employs a 100 MHz intensity-modulated optical beam. By measuring the corresponding phase delay of a mixed optical signal at 455 kHz from a corner reflector, placed at various locations on a rail of 60 cm in length, the speed of light can be precisely determined within 5% accuracy by means of curve-fitting.


In addition, it can be expanded to measure the refractive index of various media such as organic glass, synthetic quartz, and liquid by using an optional media tube.

The instruction manual contains comprehensive materials including experimental configurations, principle and step-by-step instructions. Please click Experiment Theoryand Contents to find more information about this apparatus.


Light SourceSemiconductor Laser<3 mW @ 650 nm
Length of Rail0.6 m
Signal Modulation Frequency100 MHz
Phase Measurement Frequency455 kHz
Length of Round-Trip Optical Path0 ~ 1.0 m (retroreflector travel 0 ~ 0.5 m)
Measurement Error of Speed of Light5% or better

Part List

Main Unit1
BNC Cable2
Transparent Liquid Tube with Support Carriersoptional

     LEOI-24 Apparatus for Measuring Speed of Light.jpg

Schematic of diagram

(Click figure to enlarge)


Position vs phase delay

(Click figure to enlarge)

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