Magnetism and Electromagnetism
A certain amount of current flows through a ring shaped coil with fixed number of turns. How does the magnetic induction B varies inside the coil if an iron core is threaded into coil without dimensional change of coil?

Decreases
First increases and then decreases depending on the depth of iron in¬sertion
Increases
Remains same

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Magnetism and Electromagnetism
The magnetomotive force is

The passage of magnetic field through an exciting coil
The flow of an electric current
The voltage across the two ends of exciting coil
The sum of all currents embraced by one line of magnetic field

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