Coupling

Q. Two parallel wires carrying equal currents in opposite directions are placed at x=±a parallel to y-axis with z=0. Magnetic field at origin O is B1 and at P(2a, 0, 0) is B2. Then, the ratio B1/B2 is. A .

Q. The restoring force for a magnet oscillating in a vibration magnetometer is provided by

1. Both (a) & (c)
2. torsion in the suspended thread
3. horizental component of earth's magnetic field
4. gravity

Q. Two coils of self inductance $L_1$and $L_2$ are placed closer to each other so that total flux in one coil is completely linked with other. If is mutual inductance between them, then

1. $M=L_1{L}_2$
2. $M=\frac{L_1}{L_2}$
3. $M=\sqrt{L_1}{L}_2$
4. $M=(L_1{L}_2{)}^2$

Q. The current density in a wire of radius $‘a^{\prime }$ varies with radial distance $‘r^{\prime }$ as $J=k{r}^2$ , where $k$ is a constant .

1. The total current passing through the cross section of the wire is $I=\frac{\pi k{a}^4}{2}$
2. The total current passing through the cross section of the wire is $I=\frac{3\pi k{a}^4}{2}$
3. The magnetic field at a distance $r>a$ is $B=\frac{{\mu }_{0}k{a}^4}{4r}$
4. The magnetic field at a distance $r<a$ is $B=\frac{{\mu }_{0}k{r}^3}{4}$