Archive for 27th September 2015

Direct Measurement of the Speed of Light using a Cheap Laser Diode – I

Speed of light c in air can be measured either directly or indirectly. There are many ways to infer c with indirect measurements. For instance, we can measure the propagation delay of a signal through a coaxial cable (or an optical fiber) using the TDR analysis. With the length of the coax or optical fiber known, the speed of light can be calculated using the known velocity factor (or the refractive index of the fiber) and the measured propagation delay. Another example of indirect measurement is to measure the wavelength of a known frequency standing wave (e.g. a microwave signal) and derive the phase velocity of the electromagnetic wave in air. Continue reading ‘Direct Measurement of the Speed of Light using a Cheap Laser Diode – I’ »