JEE Main 2020 (Online) 7th January Evening Slot

An emf of 20 V is applied at time t = 0 to a circuit containing in series 10 mH inductor and 5 \(\Omega\)
resistor. The ratio of the currents at time t = \(\infty\) and at t = 40 s is close to : (Take e2 = 7.389)

The activity of a radioactive sample falls from 700 s–1 to 500 s–1 in 30 minutes. Its half life is close
to:

A 60 pF capacitor is fully charged by a 20 V supply. It is then disconnected from the supply and
is conneced to another uncharged 60 pF capacitor in parallel. The electrostatic energy that is lost
in this process by the time the charge is r...

In a building there are 15 bulbs of 45 W, 15 bulbs of 100 W, 15 small fans of 10 W and 2 heaters
of 1 kW. The voltage of electric main is 220 V. The minimum fuse capacity (rated value) of the
building will be :

The balancing length for a cell is 560 cm in a potentiometer experiment. When an external
resistance of 10 \(\Omega\) is connected in parallel to the cell, the balancing length changes by 60 cm. If
the internal resistance of the ceil is $$...

An electron (of mass m) and a photon have the same energy E in the range of a few eV. The ratio
of the de-Broglie wavelength associated with the electron and the wavelength of the photon is (c
= speed of light in vaccuum)

A planar loop of wire rotates in a uniform magnetic field. Initially at t = 0, the plane of the loop
is perpendicular to the magnetic field. If it rotates with a period of 10 s about an axis in its plane
then the magnitude of induced emf wi...

The electric field of a plane electromagnetic wave is given by
\(\overrightarrow E = {E_0}{{\widehat i + \widehat j} \over {\sqrt 2 }}\cos \left( {kz + \omega t} \right)\)
At t = 0, a positively charged particle is at the point (x, y, z) =...

In the figure, potential difference between A and B is :

A thin lens made of glass (refractive index = 1.5) of focal length f = 16 cm is immersed in a liquid
of refractive index 1.42. If its focal length in liquid is f1
, then the ratio \({{{f_1}} \over f}\) is closest to the
integer :

A box weight 196 N on a spring balance at the north pole. Its weight recorded on the same
balance if it is shifted to the equator is close to (Take g = 10 ms–2 at the north pole and the radius
of the earth = 6400 km) :

Two ideal Carnot engines operate in cascade (all heat given up by one engine is used by the other
engine to produce work) between temperature, T1
and T2
. The temperature of the hot reservoir of
the first engine is T1
and the temperature ...

M grams of steam at 100oC is mixed with 200 g of ice at its melting point in a thermally insulated
container. If it produced liquid water at 40oC [heat of vaporization of water is 540 cal/g and heat
of fusion of ice is 80 cal/g] the value o...

Under an adiabatic process, the volume of an ideal gas gets doubled. Consequently the mean
collision time between the gas molecule changes from \({\tau _1}\)
to \({\tau _2}\)
. If \({{{C_p}} \over {{C_v}}} = \gamma\) for this gas then a g...

A mass of 10 kg is suspended by a rope of length 4 m, from the ceiling. A force F is applied
horizontally at the mid point of the rope such that the top half of the rope makes an angle of 45o
with the vertical. Then F equal : (Take g = 10 m...

The figure gives experimentally measured B vs H variation in a ferromagnetic material. The
retentivity, coercivity and saturation, respectively, of the material are :

A particle of mass m and charge q has an initial velocity \(\overrightarrow v = {v_0}\widehat j\)
. If an electric field \(\overrightarrow E = {E_0}\widehat i\)
and
magnetic field \(\overrightarrow B = {B_0}\widehat i\)
act on the part...

An ideal fluid flows (laminar flow) through a pipe of non-uniform diameter. The maximum and
minimum diameters of the pipes are 6.4 cm and 4.8 cm, respectively. The ratio of the minimum
and the maximum velocities of fluid in this pipe is :

Consider a uniform cubical box of side a on a rough floor that is to be moved by applying
minimum possible force F at a point b above its centre of mass (see figure). If the coefficient of
friction is \(\mu\) = 0.4, the maximum possible v...

Mass per unit area of a circular disc of radius \(a\) depends on the distance r from its centre as \(\sigma \left( r \right)\) = A + Br
. The moment of inertia of the disc about the axis, perpendicular to the plane and
assing through its ce...

The dimension of \({{{B^2}} \over {2{\mu _0}}}\), where B is magnetic field and \({{\mu _0}}\)
is the magnetic permeability of vacuum,
is :

The sum of two forces \(\overrightarrow P\)
and \(\overrightarrow Q\)
is \(\overrightarrow R\)
such that \(\left| {\overrightarrow R } \right| = \left| {\overrightarrow P } \right|\)
. The angle \(\theta\) (in degrees) that the
resul...

In a Young's double slit experiment, the separation between the slits is 0.15 mm. in the experiment,
a source of light of wavelengh 589 nm is used and the interference pattern is observed on a
screen kept 1.5 m away. The separation between ...

A stationary observer receives sound from two identical tuning forks, one of which approaches
and the other one recedes with the same speed (much less than the speed of sound). The
observer hears 2 beats/sec. The oscillation frequency of ea...

An elevator in a building can carry a maximum of 10 persons, with the average mass of each
person being 68 kg, The mass of the elevator itself is 920 kg and it moves with a constant speed
of 3 m/s. The frictional force opposing the motion i...