Measuring the velocity of light is typically not done by directly comparing it to the velocity of electrons in a circuit. Instead, various indirect methods are used that rely on the known properties of light and its interactions with matter. Here are a few commonly used techniques:
Time of Flight: One method involves measuring the time it takes for light to travel a known distance. By accurately measuring the distance and the time it takes for light to traverse that distance, the velocity of light can be calculated. This can be done using precise timing devices and carefully calibrated equipment.
Interferometry: Interferometry involves splitting a beam of light into two paths and recombining them. By measuring the interference pattern produced when the paths are combined, the wavelength of light can be determined. When combined with the frequency of light, which can be measured with high accuracy using atomic clocks, the velocity of light can be calculated.
Resonance Methods: Certain materials exhibit resonance effects when exposed to specific frequencies of light. By studying the resonant behavior of these materials, the velocity of light can be determined indirectly. For example, Fabry-Perot etalons or cavity resonators can be used to study the resonant behavior of light within them, allowing for measurements of the velocity of light.
Electromagnetic Constants: The velocity of light is related to other fundamental constants of nature, such as the permeability and permittivity of free space. Precise measurements of these constants, combined with the relationships between them, allow for the calculation of the velocity of light.
It's important to note that the maximum velocity of electrons in a circuit, which you mentioned as 10^6 m/s, is unrelated to the measurement of the velocity of light. The velocity of electrons in a circuit is determined by the properties of the conducting material, the electrical potential, and the resistance encountered in the circuit. It is not directly related to the speed of light.