### JEE Mains Previous Years Questions with Solutions

4.5
star star star star star
1

### AIEEE 2002

If an electron and a proton having same momentum enter perpendicular to a magnetic field, then
A
curved path of electron and proton will be same (ignoring the sense of revolution)
B
they will move undeflected
C
curved path of electron is more curved than that of the proton
D
path of proton is more curved.

## Explanation

KEY CONCEPT : When a charged particle enters perpendicular to a magnetic field,

then it moves in a circular path of radius.

$r = {p \over {qB}}$

where $q=$ Charge of the particle

$p=$ Momentum of the particle

$B=$ Magnetic field

Here $p,q$ and $B$ are constant for electron and proton, therefore the radius will be

same.
2

### AIEEE 2002

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

## Explanation

KEY CONCEPT : We know that the magnetic field produced by a current carrying circular coil of radius $r$

at its center is $B = {{{\mu _0}} \over {4\pi }}{I \over r} \times 2\pi$

Here ${B_A} = {{{\mu _0}} \over {4\pi }}{I \over R} \times 2\pi$ and

${B_B} = {{{\mu _0}} \over {4\pi }}{{2I} \over {2R}} \times 2\pi$

$\Rightarrow {{{B_A}} \over {B{}_B}} = 1$