JEE MAIN - Physics (2020 - 8th January Morning Slot)
1
Consider two solid spheres of radii R1 = 1m,
R2 = 2m and masses M1 and M2, respectively.
The gravitational field due to sphere (1) and (2) are shown. The value of $${{{M_1}} \over {{M_2}}}$$ is :
Answer
(B)
$${1 \over 6}$$
2
The plot that depicts the behavior of the mean
free time t (time between two successive
collisions) for the molecules of an ideal gas, as
a function of temperature (T), qualitatively, is:
(Graphs are schematic and not drawn to scale)
Answer
(B)
3
The coordinates of centre of mass of a uniform
flag shaped lamina (thin flat plate) of mass 4kg.
(The coordinates of the same are shown in
figure) are :
Answer
(A)
(0.75m, 1.75m)
4
Photon with kinetic energy of 1MeV moves
from south to north. It gets an acceleration of
1012 m/s2 by an applied magnetic field (west to
east). The value of magnetic field : (Rest mass
of proton is 1.6 × 10–27 kg) :
Answer
(A)
0.71mT
5
When photon of energy 4.0 eV strikes the
surface of a metal A, the ejected photoelectrons
have maximum kinetic energy TA eV end
de-Broglie wavelength $$\lambda _A$$. The maximum
kinetic energy of photoelectrons liberated from
another metal B by photon of energy 4.50 eV
is TB = (TA – 1.5) eV. If the de-Broglie
wavelength of these photoelectrons $$\lambda _B$$ = 2$$\lambda _A$$,
then the work function of metal B is :
Answer
(B)
4eV
6
Consider a uniform rod of mass M = 4m and
length $$\ell $$ pivoted about its centre. A mass m
moving with velocity v making angle $$\theta = {\pi \over 4}$$ to
the rod's long axis collides with one end of the
rod and sticks to it. The angular speed of the
rod-mass system just after the collision is :
Answer
(A)
$${{3\sqrt 2 } \over 7}{v \over \ell }$$
7
Consider a solid sphere of radius R and mass
density $$\rho \left( r \right) = {\rho _0}\left( {1 - {{{r^2}} \over {{R^2}}}} \right)$$ , $$0 < r \le R$$ The
minimum density of a liquid in which it will
float is :
Answer
(B)
$${{2{\rho _0}} \over 5}$$
8
In finding the electric field using Gauss Law
the formula $$\left| {\overrightarrow E } \right| = {{{q_{enc}}} \over {{\varepsilon _0}\left| A \right|}}$$ is applicable. In the
formula $${{\varepsilon _0}}$$ is permittivity of free space, A is the
area of Gaussian surface and qenc is charge
enclosed by the Gaussian surface. The equation
can be used in which of the following situation?
Answer
(D)
Only when the Gaussian surface is an
equipotential surface and $$\left| {\overrightarrow E } \right|$$ is constant on
the surface.
9
The graph which depicts the results of
Rutherford gold foil experiment with
$$\alpha $$-particales is :
$$\theta $$ : Scattering angle
Y : Number of scattered $$\alpha $$-particles detected
(Plots are schematic and not to scale)
Answer
(C)
10
A particle of mass m is fixed to one end of a
light spring having force constant k and
unstretched length $$\ell $$. The other end is fixed. The
system is given an angular speed $$\omega $$ about the
fixed end of the spring such that it rotates in a
circle in gravity free space. Then the stretch in
the spring is :
At time t = 0 magnetic field of 1000 Gauss is
passing perpendicularly through the area
defined by the closed loop shown in the figure.
If the magnetic field reduces linearly to
500 Gauss, in the next 5s, then induced EMF
in the loop is :
Answer
(C)
56 μV
12
Four resistances of 15$$\Omega $$, 12$$\Omega $$, 4$$\Omega $$ and 10$$\Omega $$
respectively in cyclic order to form
Wheatstone's network. The resistance that
is to be connected in parallel with the
resistance of 10$$\Omega $$ to balance the network is
_____$$\Omega $$.
Answer
10
13
A body A, of mass m = 0.1 kg has an initial
velocity of 3$$\widehat i$$ ms-1 . It collides elastically with
another body, B of the same mass which has
an initial velocity of 5$$\widehat j$$ ms-1. After collision,
A moves with a velocity $$\overrightarrow v = 4\left( {\widehat i + \widehat j} \right)$$. The
energy of B after collision is written as $${x \over {10}}$$. The value of x is ___________.
Answer
1
14
Effective capacitance of parallel combination
of two capacitors C1 and C2 is 10 μF. When
these capacitors are individually connected to
a voltage source of 1V, the energy stored in the
capacitor C2 is 4 times that of C1. If these
capacitors are connected in series, their
effective capacitance will be :
Answer
(C)
1.6 μF
15
Four resistances of 15$$\Omega $$, 12$$\Omega $$, 4$$\Omega $$ and 10$$\Omega $$
respectively in cyclic order to form
Wheatstone's network. The resistance that
is to be connected in parallel with the
resistance of 10$$\Omega $$ to balance the network is
_____$$\Omega $$.
Answer
10
16
A particle of mass m is fixed to one end of a
light spring having force constant k and
unstretched length $$\ell $$. The other end is fixed. The
system is given an angular speed $$\omega $$ about the
fixed end of the spring such that it rotates in a
circle in gravity free space. Then the stretch in
the spring is :
A leak proof cylinder of length 1m, made of
a metal which has very low coefficient of
expansion is floating vertically in water at 0°C
such that its height above the water surface is
20 cm. When the temperature of water is
increased to 4°C, the height of the cylinder
above the water surface becomes 21 cm. The
density of water at T = 4°C, relative to the
density at T = 0°C is close to :
Answer
(C)
1.01
18
Boolean relation at the output stage-Y for the
following circuit is :
Answer
(C)
$$\overline A .\overline B $$
19
Three charged particle A, B and C with charges
–4q, 2q and –2q are present on the
circumference of a circle of radius d. the charged
particles A, C and centre O of the circle formed
an equilateral triangle as shown in figure. Electric
field at O along x-direction is :
The critical angle of a medium for a specific wavelength, if the medium has relative permittivity 3 and relative permeability $${4 \over 3}$$ for this wavelength, will be :
Answer
(C)
30°
21
At time t = 0 magnetic field of 1000 Gauss is
passing perpendicularly through the area
defined by the closed loop shown in the figure.
If the magnetic field reduces linearly to
500 Gauss, in the next 5s, then induced EMF
in the loop is :
Answer
(C)
56 μV
22
The magnifying power of a telescope with tube
60 cm is 5. What is the focal length of its eye
piece ?
Answer
(B)
10 cm
23
The dimension of stopping potential V0 in photoelectric effect in units of Planck's constant 'h', speed of light 'c' and Gravitational constant 'G' and ampere A is :
Answer
(B)
h0 c5 G-1 A-1
24
A thermodynamic cycle xyzx is shown on a V-T diagram.
The P-V diagram that best describes this cycle
is : (Diagrams are schematic and not to scale)