In a $dc$ motor, induced $e.m.f.$ will be maximum

A coil of radius $1\, cm$ and of turns $100$ is placed in the middle of a long solenoid of  radius $5\, cm$. and having $5\, turns/cm$. parallel to the axis of solenoid The mutual  inductance in millihenery will be

An electric current $i_1$ can flow either direction through loop $(1)$ and induced current $i_2$ in loop $(2)$. Positive $i_1$ is when current is from $'a'$ to $'b'$ in loop $(1)$ and positive $i_2$ is when the current is from $'c'$ to $'d'$ in loop $(2)$ In an experiment, the graph of $i_2$ against time $'t'$ is as shown below Which one $(s)$ of the following graphs could have caused $i_2$ to behave as give above.

If a current of $3.0$ $amperes$ flowing in the primary coil is reduced to zero in $0.001$ $second,$ then the induced $e.m.f$ in the secondary coil is $15000$ $volts$. The mutual inductance between the two coils is....$henry$

Two coaxial coils are very close to each other and their mutual inductance is $5 \,mH$. If a current $50 sin 500 \,t$ is passed in one of the coils then the peak value of induced e.m.f in the secondary coil will be ........... $V$

A solenoid has $2000$ turns wound over a length of $0.3\,m$. The area of cross-section is $1.2\times10^{-3}\,m^2$. Around its central section a coil of $300$ turns is closely wound. If an initial current of $1\,A$ is reversed in $0.25\,s$. Find the emf induced in the coil.......$mV$