 JEE Mains Previous Years Questions with Solutions

4.5
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1

AIEEE 2002

Wavelength of light used in an optical instrument are ${\lambda _1} = 4000\mathop A\limits^ \circ$ and ${\lambda _2} = 5000\mathop A\limits^ \circ ,$ then ratio of their respective resolving powers (corresponding to ${\lambda _1}$ and ${\lambda _2}$ ) is
A
$16:25$
B
$9:1$
C
$4:5$
D
$5:4$

Explanation

${{{{\left( {R.P} \right)}_1}} \over {{{\left( {R.P} \right)}_2}}} = {{{\lambda _2}} \over {{\lambda _1}}} = {5 \over 4}$
2

AIEEE 2002

If two mirrors are kept at ${60^ \circ }$ to each other, then the number of images formed by them is
A
$5$
B
$6$
C
$7$
D
$8$

Explanation

KEY CONCEPT : When two plane mirrors are inclined a each other at an angle $\theta$ then the number of the images of a point object placed between the plane mirrors is

${{{{360}^ \circ }} \over \theta } - 1,\,\,if{{{{360}^ \circ }} \over \theta }$ is even

$\therefore$ Number of images formed

$= {{{{360}^ \circ }} \over {{{60}^ \circ }}} - 1 = 5$
3

AIEEE 2002

Electromagnetic waves are transverse in nature is evident by
A
polarization
B
interference
C
reflection
D
diffraction

Explanation

The phenomenon of polarisation is shown only by transverse waves.
4

AIEEE 2002

An astronomical telescope has a large aperture to
A
reduce spherical aberration
B
have high resolution
C
increase span of observation
D
have low dispersion

Explanation

KEY CONCEPT : The resolving power of a telescope

$R.P = {D \over {122\lambda }}$ where $D=$ diameter of the objective lens

$\lambda =$ wavelength of light.

Clearly, larger the aperture, larger is the value of $D,$

more is the resolving power or resolution.