The flux linked with the coil at any instant ' t ' is given by $\phi=12 t^2-60 t+275$. The magnitude of induced e.m.f. at $\mathrm{t}=3 \mathrm{~second}$ is

A coil of area $12 \mathrm{~cm}^2$ has 250 turns. Magnetic field of $0.2 \mathrm{~Wb} / \mathrm{m}^2$ is perpendicular to the plane of the coil. The field is reduced to $0.1 \mathrm{~Wb} / \mathrm{m}^2$ in 0.1 second. The magnitude of induced e.m.f. in the coil is

Two different coils have self - inductance $\mathrm{L}_1=9 \mathrm{mH}$ and $\mathrm{L}_2=3 \mathrm{mH}$. The current in first coil is increased at a constant rate. The current in the second coil is also increased at the same constant rate. At certain instant of time, the power given to the two coils is same. At that time, there was current and induced voltage in the two coils. At the same instant, the ratio of the energy stored in the first coil to that in second coil is

Figure shows a rectangular frame situated in a constant magnetic field. A wire BC of length 1 m is moved out with velocity $4 \mathrm{~m} / \mathrm{s}$. Magnetic field strength is 0.15 T . Force acting on the wire $B C$ is