$A B$ is a part of an electrical circuit (see figure). The potential difference " $V_A-V_B$ ", at the instant when current $i=2 \mathrm{~A}$ and is increasing at a rate of $1 \mathrm{amp} /$ second is:

Let us consider two solenoids $$A$$ and $$B$$, made from same magnetic material of relative permeability $$\mu_r$$ and equal area of cross-section. Length of $$A$$ is twice that of $$B$$ and the number of turns per unit length in $$A$$ is half that of $$B$$. The ratio of self inductances of the two solenoids, $$L_A: L_B$$ is

An emf is generated by an ac generator having 100 turn coil, of loop area $$1 \mathrm{~m}^2$$. The coil rotates at a speed of one revolution per second and placed in a uniform magnetic field of $$0.05 \mathrm{~T}$$ perpendicular to the axis of rotation of the coil. The maximum value of emf is :-

The net magnetic flux through any closed surface is :