electromagnetic  waves    The Maxwell's equations* in free space

curl E = - [¶ B/¶ t]

and curl B =m _o e _o [¶ E/¶ t]

show that E and B  fields  are  interrelated,  that is whenever there is a changing B field there exists an associated E field, and similarly changing E field  has  an associated  B  field. This was first observed by Maxwell  who  proposed  the existence of electromagnetic waves in which  electric  and  magnetic  fields propagate simultaneously. Solving the equations written above, we obtain the equation of wave motion  for  E  and B fields, having exactly the same form as any other wave motion. These are

and (e6)

[¶ ²E/ ¶ x²] = m _o e _o [¶ ²E/ ¶ t²] and [¶ ²B/ ¶ x²] = m _o e _o [¶ ²B/ ¶ t²]

The velocity of the wave is (e _{0m 0})^-1/2, the numerical value of  which  is that of velocity of light. In fig.e3 the nature of the  waves  is  depicted. The electric field vector and magnetic field  vector  oscillate perpendicular to each other and they are perpendicular  to  the direction of propagation. In appendix V the spectrum  of electromagnetic  waves  is  given.  Only  a  small part in the spectrum produces sensation on our eyes and we call it light.