<Ul> <Li> e − i ω t (\ displaystyle \, e ^ (- i \ omega t)) (mainly used by physicists) </Li> <Li> e + j ω t (\ displaystyle \, e ^ (+ j \ omega t)) (mainly used by engineers) </Li> </Ul> <Li> e − i ω t (\ displaystyle \, e ^ (- i \ omega t)) (mainly used by physicists) </Li> <Li> e + j ω t (\ displaystyle \, e ^ (+ j \ omega t)) (mainly used by engineers) </Li> <Li> The sign for the imaginary part of permittivity (in fact dictated by the choice of sign for time - dependence) </Li>

What is meant by an appropriate sign convention