Electromagnets are created by (2 points) a. applying a charge to a magnetic material, wrapped in an insulator, which creates an electromagnetic field around the magnet. b. covering a magnet with insulation and applying an alternating electrical current to the magnet. c. twisting a ferromagnetic material, wrapping in an insulator, and applying a direct current to the coil. d. wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.

I believe the correct answer is B

The answer is D

Explanation:

i took the test

a solenoid is created by wrapping a l = 90 m long wire around a hollow tube of diameter d = 4.5 cm.   the wire diameter is d = 0.9 mm.   the solenoid wire is then connected to a power supply so that a current of i = 9 a flows through the wire.

randomized variablesl = 90 m

d = 4.5 cm

d = 0.9 mm

i = 9 a                                          

write an expression for the number of turns, n, in the solenoid. you do not need to take into account the diameter of the wire in this calculation.

calculate the number of turns, n, in the solenoid.

write an expression for the length of the solenoid (l2) in terms of the diameter of the hollow tube d.

calculate the length of the solenoid (l2)   in meters.

calculate the magnitude of the magnetic field at the center of the solenoid in teslas.

explanation:

answer: electrons