In the context of magnetic circuits, if a bar magnet is placed on paper and iron filings are sprinkled around the magnet, the iron filings form closed lines. These lines are called lines of _______.

In a magnetic circuit, the Magnetomotive Force (MMF) is equal to the product of _________.

If the permeability μ of a material is increased, the reluctance of the composite magnetic circuit ___________.

An air gap is introduced into a closed magnetic circuit. What happens to the magnetic flux if the MMF remains constant?