To produce a magnetic field, What does an electromagnet require? A) a solenoid with no current flowing through it.
B) a core made from a magnetic material.
C) a current flowing through a coil of wire.
D) a copper core.

1. do the particles in the medium material move in the same direction of the wave or at opposite direction to the wave? explain your answer. 2. by inputting more energy into the wave, i.e a large shake of the spring, which wave property also increases? 3. are there forces of friction acting while a wave is passing through a medium?