D. C. Pandey Solutions for Chapter: Magnetic Effects of Current, Exercise 7: [ Level 2 ]

Assertion: Net torque in the current-carrying loop placed in a uniform magnetic field (pointing inwards) is zero.

Reason: Magnetic moment is inwards.

Assertion: A charged particle is rotating in a circle. Then, magnetic field at centre of circle and magnetic moment produced by motion of charged particle are parallel to each other.

Reason: $M$ and $B$ are always parallel to each other.

Assertion: If a charged particle enters from outside in uniform magnetic field then it will keep on rotating in a circular path.

Reason: Magnetic force is always perpendicular to velocity vector.

Assertion: Magnetic field and electric field are present in a region. The net force on a charged particle in this region is zero if

$\overrightarrow{E}=\overrightarrow{B}\times \overrightarrow{v}$.

Reason: $\frac{E}{B}$ has the dimensions of velocity.

Assertion: An $\alpha -$particle and a deuteron having the same kinetic energy enter in uniform magnetic field perpendicular to the field. Then the radius of the circular path of $\alpha$-particle will be more.

Reason: $\frac{q}{m}$ ratio of an $\alpha -$particle is more than the $\frac{q}{m}$ ratio of a deuteron.

Assertion: A charged particle is rotating in a circular path in uniform magnetic field. Then, plane of circle is perpendicular to the magnetic field.

Reason: Circular motion is a two-dimensional motion.

Assertion: At the centre of a circular current carrying loop $I_1$, there is an infinitely long straight current carrying wire $I_2$ perpendicular to the plane of the circle. Then, magnetic force of attraction between two is zero.

Reason: Magnetic field of $I_1$ at centre is inwards, parallel to $I_2$.

Assertion: If the velocity of charged particle in a uniform magnetic field at some instant is, $\left(a_1\hat{\mathrm{i}}-a_2\hat{\mathrm{j}}\right)$ and at some other instant is $\left(b_1\hat{\mathrm{i}}+b_2\hat{\mathrm{j}}\right)$, then $a_1^2+a_2^2=b_1^2+b_2^2$.

Reason: Magnetic force cannot change velocity of a charged particle.