4. Write down the equations of transformations for electromagnetic fields in two inertial frames S and S' in relative motion. Use these to show that what is observed to be a pure electric or pure magnetic field in one frame is observed to have both electric as well as magnetic components in the other frame. 5. Derive an expression for the electric field generated by an electric charge in uniform motion relative to an observer. Explain how the field varies in the direction along and transverse to the motion of the charge. 6. An electric charge is in uniform motion relative to an inertial frame S. Obtain expressions for the electric and magnetic fields observed by an observer in frame S.