Question

A solenoid is a coil of wire that produces a magnetic field when carrying an electric current. The strength of the magnetic field produced by a solenoid can be increased in two basic ways: increasing the number of loops in the solenoid or increasing the amount of current running through the solenoid. A solenoid's magnetic field can be increased to an even greater degree by wrapping the wire around a material that can be magnetized. Four solenoids are shown below.

solenoid%20with%20wire%20only solenoid%20with%20wire%20only
Solenoid A
Copper Wire Only
Current: 6 amps Solenoid B
Copper Wire Only
Current: 8 amps

solenoid%20with%20iron%20core solenoid%20with%20iron%20core
Solenoid C
Copper Wire + Iron Core
Current: 6 amps Solenoid D
Copper Wire + Iron Core
Current: 8 amps

Based on the strength of the magnetic fields they produce, arrange the solenoids from strongest to weakest.

Solenoid A
Solenoid B
Solenoid C
Solenoid D
> > >

Answer 1

D (Solenoid D) > C (Solenoid C) > B (Solenoid B) > A (Solenoid A)

Reason: B ∝ μ n I. Adding an iron core (higher μ) increases the field more than the same increase in current, and higher current increases the field, so 8 A with iron (D) is strongest, 6 A with iron (C) next, then 8 A without iron (B), and 6 A without iron (A) weakest.