Question

A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, then the current in the coil

• A. will not change
• B. will increase
• C. will decrease
• D. may increase or decrease depending upon the direction of the current

Hint:

While the core is being pushed in, the flux grows, and the induced emf opposes the battery.

Answer 1

The Correct Option is C

Step 1: Understand the concept
The battery drives a steady current through the solenoid. Inserting an iron core increases the inductance, so the magnetic flux linked with the coil increases while the core moves in.

Step 2: Apply Lenz's law
A rising flux induces an emf that opposes the change, that is, an emf that acts against the battery emf. This opposing induced emf is \(-\dfrac{d\Phi}{dt}\) in size.

Step 3: Effect on the current
The net emf in the circuit is the battery emf minus the induced emf, so the current in the coil decreases while the core is being inserted.

Step 4: Result
The current decreases, option (C). The direction of the current does not matter, because the induced emf always opposes the change in flux, so (D) is not needed, and (A) and (B) ignore the induced emf.

Final Answer:
The current decreases during insertion because the induced emf opposes the battery. This is option (C). \[ \boxed{\text{(C) }\text{Decreases}} \]