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: Energy and flux
Moving the iron into the coil raises the flux linkage of the coil.

Step 2: Induced emf
By Faraday's law, an emf appears in the coil. By Lenz's law it opposes the flux increase, which means it opposes the current that produces the flux.

Step 3: Current
With the induced emf acting against the battery, $I = \dfrac{\varepsilon - |\varepsilon_{ind}|}{R}$ is less than before.

Step 4: Answer
The current decreases, option (C).

Final Answer:
The current decreases while the core is inserted. This is option (C). \[ \boxed{\text{(C) }\text{Decreases}} \]