When a positively charged particle enters into a uniform magnetic field with uniform velocity, its trajectory can be

(i) a straight line  (ii) a circle  (iii) a helix

• (i) only

• (i) or (ii)

• (i) or (iii)

• any one of (i), (ii) and (iii)

Assertion: Magnetic field lines are continuous and closed.

Reason: Magnetic monopole does not exist.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  Magnetic force between two short magnets, when they are co-axial follows inverse square law of distance. 

Reason:  The magnetic forces between two poles do not follow inverse square law of distance.

• If both assertion and reason are true and reaon is correct explanation of assertion.

• If both assertion and reason are true and reaon is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  If  a proton and an a-particle enter a uniform magnetic field perpendicularly with the same speed, the time period of revolution of a particle is double that of proton. 

Reason:  In a magnetic field, the period of revolution of a charged particle is directly proportional to the mass of the particle and is inversely proportional to charge of particle.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false.

A  moving  coil  galvanometer  has  a resistance  of  900 Ω.  In order  to send  only 10 % of  the  main  current through  this  galvanometer,  the  resistance  of  the required  shunt  is

• 0.9 Ω

• 100 Ω

• 405 Ω

• 90 Ω

The intensity of magnetic field due to an isolated pole of strength m_p at a point distant r from it will be

• m_p/r²

• m_p r²

• r²/ m_p

• m_p/r

87.

The  ratio of magnetic fields on the axis of a circular current carrying coil of radius a to the magnetic field at its centre will be

• $\frac{1}{{\left(1 + {\displaystyle \frac{{\mathrm{x}}^2}{{\mathrm{a}}^2}}\right)}^{{\displaystyle \raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}}$

• $\frac{1}{{\left(1 + {\displaystyle \frac{{\mathrm{a}}^2}{{\mathrm{x}}^2}}\right)}^{{\displaystyle \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}}$

• $\frac{1}{{\left(1 + {\displaystyle \frac{{\mathrm{a}}^2}{{\mathrm{x}}^2}}\right)}^2}$

• $\frac{1}{{\left(1 + {\displaystyle \frac{{\mathrm{a}}^2}{{\mathrm{x}}^2}}\right)}^3}$

Assertion:  When a radius of circular loop carrying current is doubled, its magnetic moment becomes four times.

Reason: Magnetic moment depends on area of the loop.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

What is the magnetic field at a distance R from a coil of radius r carrying current ?

• $\frac{{\mathrm{\mu }}_0 \mathrm{I} {\mathrm{R}}^2}{2 {\left( {\mathrm{R}}^2 + {\mathrm{r}}^2 \right)}^{{\displaystyle \raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}}$

• $\frac{{\mathrm{\mu }}_0\mathrm{I} {\mathrm{R}}^2}{2 {\left( {\mathrm{R}}^2 + {\mathrm{r}}^2 \right)}^{{\displaystyle \raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}}$

• $\frac{{\mathrm{\mu }}_0 \mathrm{I}}{2\mathrm{r}}$

• $\frac{{\mathrm{\mu }}_0 \mathrm{I}}{2\mathrm{R}}$

In the following diagram, which particle has highest e/m value?

• A

• B

• C

• D