The second LED is required for the capacitive example because without it all of the charge would eventually accumulate on one plate. This isn't a problem with t

The second LED is required for the capacitive example because without it all of the charge would eventually accumulate on one plate. This isn't a problem with the coil as there is a complete circuit for the charge to move around. He is not saying the magnetic field is not alternating (he even says the coil is being driven by a 1 MHz sine wave). The current in the coil is not alternating, because of the LED.