Magnetic Effects of Current & Magnetism · JEE Main previous year questions

A magnetic needle is kept in a non-uniform magnetic field. It experiences :

1. A.neither a force nor a torque
2. B.a torque but not a force
3. C.a force but not a torque
4. D.a force and a torque

1. A.$-Blv$
2. B.$Blv$
3. C.$2Blv$
4. D.$\mathrm{zero}$

A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is $B$. It is then bent into a circular loop of $n$ turns. The magnetic field at the center of the coil will be

1. A.$2nB$
2. B.$n^{2}B$
3. C.$nB$
4. D.$2n^{2}B$

The magnetic field due to a current carrying circular loop of radius $3\mathrm{cm}$ at a point on the axis at a distance of $4\mathrm{cm}$ from the centre is $54\mu \mathrm{T}$. What will be its value at the center of loop?

1. A.$125\mu \mathrm{T}$
2. B.$150\mu \mathrm{T}$
3. C.$250\mu \mathrm{T}$
4. D.$75\mu \mathrm{T}$

A metal conductor of length $1\mathrm{m}$ rotates vertically about one of its ends at angular velocity $5$ radians per second. If the horizontal component of earth's magnetic field is $0.2\times 10^{-4}\mathrm{T}$, then the $e.m.f.$ developed between the two ends of the conductor is

1. A.$5\mathrm{mV}$
2. B.$50\mu \mathrm{V}$
3. C.$5\mu \mathrm{V}$
4. D.$50\mathrm{mV}$

If in a circular coil $A$ of radius $R$, current $I$ is flowing and in another coil $B$ of radius $2R$ a current $2I$ is flowing, then the ratio of the magnetic fields $B_A$ and $B_B$, produced by them will be

1. A.$1$
2. B.$2$
3. C.$1/2$
4. D.$4$

If an electron and a proton having same momentum enter perpendicular to a magnetic field, then

1. A.curved path of electron and proton will be same (ignoring the sense of revolution)
2. B.they will move undeflected
3. C.curved path of electron is more curved than that of the proton
4. D.path of proton is more curved.

The time period of a charged particle undergoing a circular motion in a uniform magnetic field is independent of its

1. A.speed
2. B.mass
3. C.charge
4. D.magnetic induction

1. A.$\frac{{\mu }_0}{2\pi r}{i}_1{i}_{2}dl\tan \theta$
2. B.$\frac{{\mu }_0}{2\pi r}{i}_1{i}_{2}dl\sin \theta$
3. C.$\frac{{\mu }_0}{2\pi r}{i}_1{i}_{2}dl\cos \theta$
4. D.$\frac{{\mu }_0}{4\pi r}{i}_1{i}_{2}dl\sin \theta$

At a specific instant emission of radioactive compound is deflected in a magnetic field. The compound can emit (i) electrons (ii) protons (iii) $\mathrm{H}{\mathrm{e}}^{2+}$ (iv) neutrons The emission at instant can be

1. A.$i,ii,iii$
2. B.$i,ii,iii,iv$
3. C.$iv$
4. D.$ii,iii$