Question

By inserting an iron core in a coil carrying current, the strength of its magnetic field will :

• A. increase
• B. decrease
• C. remain Same
• D. become Zero

Answer 1

Answer: (A)

Answer is A.

If a soft iron rod called core is placed inside a solenoid, then the strength of the magnetic field becomes very large because the iron ore is magnetized by induction. This combination of a solenoid and a soft iron core is called an electromagnet.
The soft iron core helps in concentrating the magnetic lines of forces through the solenoid, so that the magnetic field is almost uniform at the end face of the core. In the absence of a core, the magnetic lines of forces start to diverge by curving sharply immediately outside the coils. The smaller the space between the coils and the core, the stronger is the magnetism induced in the core. Therefore, the best electromagnets have coils wound tightly around the core.
Hence, the strength of the magnetic field increases when a soft iron core is inserted inside a solenoid.