Question

why light travels in straight line?explain ​

Answer 1

in dusty atmosphere it is sometimes possible to see lights travelling and it does appear to be moving in a straight line

Answer 2

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Light travels in the straight line because it does not generally interact with the medium and wherever it interacts it does change its path like when it is entering a different medium with different permeability and permittivity(denser or rarer). This interaction and bending of light is called refraction..