Question

If a ferromagnetic material is inserted in a current carrying solenoid, the magnetic field inside the solenoid

• A. increases
• B. decreases
• C. remains unchanged
• D. becomes zero

Hint:

Ferromagnets have very large relative permeability.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The field inside an air-filled solenoid is \(B_0 = \mu_0 n I\). With a core of relative permeability \(\mu_r\), the field becomes \(B = \mu_r \mu_0 n I\).

Step 2: Ferromagnetic core:
For ferromagnetic materials such as iron, \(\mu_r\) is very large, from hundreds to thousands. So \(B\) becomes much larger than \(B_0\).

Step 3: Why the other options fail:
The field cannot fall or vanish because \(\mu_r > 1\). It cannot stay unchanged because the domains of the core align with the field and add their own magnetisation.

Final Answer:
The magnetic field inside the solenoid increases. \[ \boxed{\text{Increases}} \]