JEE MAIN - Physics (2019 - 10th April Morning Slot)
1
A proton, an electron, and a Helium nucleus,
have the same energy. They are in circular
orbits in a plane due to magnetic field
perpendicualr to the plane. Let rp, re and rHe be
their respective radii, then
Answer
(B)
re < rp = rHe
2
The value of acceleration due to gravity at
Earth's surface is 9.8 ms–2. The altitude above
its surface at which the acceleration due to
gravity decreases to 4.9 ms–2, is close to :
(Radius of earth = 6.4 × 106 m)
Answer
(D)
2.6 × 106 m
3
A moving coil galvanometer allows a full scale
current of 10–4 A. A series resistance of 2 M$$\Omega $$
is required to convert the above galvanometer
into a voltmeter of range 0-5 V. Therefore the
value of shunt resistance required to convert the
above galvanometer into an ammeter of range
0.10 mA is :
Answer
(D)
None of the options are correct
4
In a photoelectric effect experiment the
threshold wavelength of the light is 380 nm. If
the wavelentgh of incident light is 260 nm, the
maximum kinetic energy of emitted electrons
will be:
Given E (in eV) = 1237/$$\lambda $$ (in nm)
Answer
(D)
1.5 eV
5
A transformer consisting of 300 turns in the
primary and 150 turns in the secondary gives
output power of 2.2 kW. If the current in the
secondary coil is 10A, then the input voltage
and current in the primary coil are :
Answer
(C)
440 V and 5A
6
In an experiment, the resistance of a material
is plotted as a function of temperature (in some
range). As shown in the figure, it is a straight
line. One may conclude that :
Answer
(D)
$$R(T) = {R_0}{e^{ - T_0^2/{T^2}}}$$
7
A ray of light AO in vacuum is incident on a
glass slab at angle 60° and refracted at angle 30°
along OB as shown in the figure. The optical path
length of light ray from A to B is:
Answer
(C)
2a + 2b
8
n moles of an ideal gas with constant volume
heat capcity CV undergo an isobaric expansion
by certain volume. The ratio of the work done
in the process, to the heat supplied is :
Answer
(D)
$${{nR} \over {{C_V} + nR}}$$
9
Two wires A & B are carrying currents I1 & I2
as shown in the figure. The separation between
them is d. A third wire C carrying a current I
is to be kept parallel to them at a distance x from
A such that the net force acting on it is zero.
The possible values of x are :
Answer
(D)
$$x = \pm {{{I_1}d} \over {{I_1} - {I_2}}}$$
10
A particle of mass m is moving along a
trajectory given by
x = x0 + a cos$$\omega $$1t
y = y0 + b sin$$\omega $$2t
The torque, acting on the particle about the
origin, at t = 0 is :
Answer
(B)
+my0a $$\omega _1^2$$$$\widehat k$$
11
The electric field of a plane electromagnetic
wave is given by
$$\overrightarrow E = {E_0}\widehat i\cos (kz)cos(\omega t)$$ The corresponding magnetic field $$\overrightarrow B $$ is then given by
Answer
(A)
$$\overrightarrow B = {{{E_0}} \over C}\widehat j\sin (kz)\sin (\omega t)$$
12
Two coaxial discs, having moments of inertia
I1 and I1/2, are rotating with respective angular
velocities $$\omega $$1 and
$$\omega $$1/2
, about their common axis.
They are brought in contact with each other and
thereafter they rotate with a common angular
velocity. If Ef and Ei are the final and initial total
energies, then (Ef - Ei) is:
Answer
(A)
$${{{I_1}\omega _1^2} \over {24}}$$
13
A thin disc of mass M and radius R has mass
per unit area $$\sigma $$(r) = kr2 where r is the distance
from its centre. Its moment of inertia about an
axis going through its centre of mass and
perpendicular to its plane is :
Answer
(C)
$${{2M{R^2}} \over 3}$$
14
A cylinder with fixed capacity of 67.2 lit
contains helium gas at STP. The amount of heat
needed to raise the temperature of the gas by
20°C is : [Given that R = 8.31 J mol–1 K–1]
Answer
(C)
748 J
15
One plano-convex and one plano-concave lens
of same radius of curvature 'R' but of different
materials are joined side by side as shown in
the figure. If the refractive index of the material
of 1 is $$\mu $$1 and that of 2 is $$\mu $$2, then the focal
length of the combination is :
Answer
(C)
$${R \over { {{\mu _1} - {\mu _2}}}}$$
16
A ball is thrown upward with an initial velocity
V0 from the surface of the earth. The motion
of the ball is affected by a drag force equal to
m$$\gamma $$u2 (where m is mass of the ball, u is its
instantaneous velocity and $$\gamma $$ is a constant).
Time taken by the ball to rise to its zenith is :
In a meter bridge experiment, the circuit
diagram and the corresponding observation
table are shown in figure
SI. No.
R($$\Omega $$)
l(cm)
1.
1000
60
2.
100
13
3.
10
1.5
4.
1
1.0
Which of the readings is inconsistent?
Answer
(A)
4
18
A current of 5 A passes through a copper
conductor (resistivity = 1.7 × 10–8 $$\Omega $$m) of radius
of cross-section 5 mm. Find the mobility of the
charges if their drift velocity is 1.1 × 10–3 m/s.
Answer
(B)
1.0 m2/Vs
19
Figure shows charge (q) versus voltage (V)
graph for series and parallel combination of two
given capacitors. The capacitances are :
Answer
(A)
40 $$\mu $$F and 10 $$\mu $$F
20
Two particles, of masses M and 2M, moving,
as shown, with speeds of 10 m/s and 5 m/s,
collide elastically at the origin. After the
collision, they move along the indicated
directions with speeds u1 and u2, respectively.
The values of u1 and u2 are nearly :
Answer
(B)
6.5 m/s and 6.3 m/s
21
The ratio of surface tensions of mercury and
water is given to be 7.5 while the ratio of thier
densities is 13.6. Their contact angles, with
glass, are close to 135° and 0°, respectively. It
is observed that mercury gets depressed by an
amount h in a capillary tube of radius r1, while
water rises by the same amount h in a capillary
tube of radius r2. The ratio, (r1/r2), is then close
to :
Answer
(A)
2/5
22
The value of acceleration due to gravity at
Earth's surface is 9.8 ms–2. The altitude above
its surface at which the acceleration due to
gravity decreases to 4.9 ms–2, is close to :
(Radius of earth = 6.4 × 106 m)
Answer
(D)
2.6 × 106 m
23
A uniformly charged ring of radius 3a and total
charge q is placed in xy-plane centred at origin.
A point charge q is moving towards the ring
along the z-axis and has speed u at z = 4a. The
minimum value of u such that it crosses the
origin is :