Which scientist showed that by changing magnetic field an electric field can be obtained?

The negative sign in Faraday's law represents which fact?

Two circular coils $A$ and $B$ are facing each other as shown in the figure. The current $i$ through coil $A$ can be altered.

As shown in the figure,a bar magnet is moving towards a stationary coil with a constant speed $v$. The direction of the induced current in the coil as observed by the observer on the $R$.$H$.$S$. is . . . . . . .

The magnetic flux through a coil perpendicular to its plane and directed into the paper is varying according to the relation $\phi = 5t^2 + 10t + 5$ milliweber. The $e.m.f.$ induced in the loop after $5 \, s$ is ..... $V$.

The coil of area $0.1 \ m^2$ has $500$ turns. After placing the coil in a magnetic field of strength $4 \times 10^{-4} \ Wb/m^2$,if it is rotated through $90^o$ in $0.1 \ s$,the average emf induced in the coil is......$V$