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.


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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