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 :
Respondre
(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)
Respondre
(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 :
Respondre
(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) :
Respondre
(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 T_A 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 T_B = (T_A – 1.5) eV. If the de-Broglie wavelength of these photoelectrons $$\lambda _B$$ = 2$$\lambda _A$$, then the work function of metal B is :
Respondre
(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 :
Respondre
(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 :
Respondre
(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 q_enc is charge enclosed by the Gaussian surface. The equation can be used in which of the following situation?
Respondre
(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)
Respondre
(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 :
Respondre
(A)
$${{m\ell {\omega ^2}} \over {k - m{\omega ^2}}}$$
11
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 :
Respondre
(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 _____$$\Omega $$.
Respondre
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 ___________.
Respondre
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 :
Respondre
(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 _____$$\Omega $$.
Respondre
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 :
Respondre
(A)
$${{m\ell {\omega ^2}} \over {k - m{\omega ^2}}}$$
17
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 :
Respondre
(C)
1.01
18
Boolean relation at the output stage-Y for the following circuit is :
Respondre
(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 :
Respondre
(C)
$${{\sqrt 3 q} \over {\pi {\varepsilon _0}{d^2}}}$$
20
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 :
Respondre
(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 :
Respondre
(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 ?
Respondre
(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 :
Respondre
(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)
Respondre
(A)