$A$ coil of $n$ turns and resistance $R \text{ } \Omega$ is connected in series with a resistance $R/4$. The combination is moved for time $t$ second through flux $\phi_1$ to $\phi_2$. The induced current in the circuit is

$A$ coil with an area of $500 \ cm^2$ and $1000$ turns is placed in a magnetic field of $2 \times 10^{-5} \ Wb/m^2$ perpendicular to its plane. If the coil is rotated by $180^o$ in $0.2 \ s$,the induced $emf$ in $milli-volts$ is:

$A$ magnetic field of flux density $1.0 \,Wb \,m^{-2}$ acts normal to a $80$ turn coil of $0.01 \,m^2$ area. If this coil is removed from the field in $0.2 \,s$, then the emf induced in it is (in $\,V$)

An aluminium ring $B$ faces an electromagnet $A$. The current $I$ through $A$ can be altered.

$A$ circular coil of radius $10 \; cm$, $500$ turns, and resistance $2 \; \Omega$ is placed with its plane perpendicular to the horizontal component of the earth's magnetic field. It is rotated about its vertical diameter through $180^{\circ}$ in $0.25 \; s$. The induced e.m.f. in the coil is (Take $B_H = 3.0 \times 10^{-5} \; T$).

$A$ long solenoid having $100$ turns per $cm$ carries a current of $\frac{4}{\pi} \,A$. At the centre of it is placed a coil of $200$ turns of cross-sectional area $25 \,cm^2$ having its axis parallel to the field produced by the solenoid. When the direction of the current in the solenoid is reversed within $0.04 \,s$, the induced emf in the coil is (in $\,V$)