Question

A solenoid is connected to a source of constant e.m.f. for a long time. A soft iron piece is inserted into it. Then, which of the following is/are correct?

• A. Self-inductance of the solenoid gets increased
• B. Flux linked with the solenoid increases; hence, steady state current gets decreased
• C. Energy stored in the solenoid gets increased
• D. Magnetic moment of the solenoid gets increased

Answer 1

Answer: (A), (C), (D)

The correct options are
A Self-inductance of the solenoid gets increased
C Energy stored in the solenoid gets increased
D Magnetic moment of the solenoid gets increased

The presence of iron core will increase the magnetic field produced by the solenoid due to high magnetic permeability of iron. The equation of solenoid with no core is
$B={\mu }_{0}Ni/l$
and the equation of solenoid with core is
$B={\mu }_0{\mu }_{r}Ni/l$
where ${\mu }_r$ is the relative permeability of the material that the core is made of. In case of magnetic iron it is equal to 200.
Self-inductance increased with the increase of the magnetic permeability of core material. Magnetic moment and the energy will also increase as the magnetic field increases.