CLARIFICATION AND DISCUSSION OF THE TIME TERM OF PLUS OR MINUS SIGN FOR ELECTROMAGNETIC WAVE FUNCTION IN THE TEXTBOOK OF PHYSICAL OPTICS

In textbooks on electromagnetic waves or optics, the time term of the electromagnetic field wave function is usually represented with a negative sign. However, in the "College Physics" textbook, the wavefunction of the wave for the time term is typically represented with a positive sign when deriving the wave equation from the vibration equation. During my teaching, students often raise such questions, so it is necessary to discuss the concept and physical significance of the positive and negative signs of the time term to better help students understand the physical significance. This paper starts from the definition of vibration, provides related concepts of wave motion, and discusses in detail the physical connotation of the positive and negative signs of the time term in the wave function of electromagnetic field. In addition, it further analyzes the practical considerations of expressing the time term of the wave function as a negative sign when dealing with electromagnetic wave or optical problems, clarifying and explaining the doubts about the wave function of electromagnetic waves usually being represented with a negative sign.