Which of the following is a true statement? a. electromagnetic waves are longitudinal waves. b. electromagnetic waves do not always need a medium to travel. c. electromagnetic waves consist of only changing electric fields. d. electromagnetic waves can vary in speed, wavelength and frequency.

Ahuge (essentially infinite) horizontal nonconducting sheet 10.0 cm thick has charge uniformly spread over both faces. the upper face carries +95.0 nc/m2 while the lower face carries -25.0 nc/ m2. what is the magnitude of the electric field at a point within the sheet 2.00 cm below the upper face? (ε0 = 8.85 × 10-12 c2/n · m2)