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What is the speed of light ? Which process is basically used for measurement ?

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- Numerically, it can be calculated using dielectric electric constant (
*ε*_{0) of vacuum and magnetic permeability constant (μ0) for vacuum. It has relation with speed of light as: c = sqrt(ε0 *μ0). The constants accurate values }are available, hence we have accurate value of c - Using light source and reflector at known distance, start flashing the light at certain interval and receive light back at source. Measure time taken (t) to travel to and fro distance from source to reflector and back. If distance between source and reflector is ‘d’ than light has taken time to travel ‘2d’. From this one can find velocity v=2d/t. The time counter to be started when light flash is transmitted and counter to be stopped when flash is received back. Time interval can be measured accurately to calculate the speed of light.