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 : JEE Main 2019 (Online) 10th April Morning Slot Physics - Current Electricity Question 238 English
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: JEE Main 2019 (Online) 10th April Morning Slot Physics - Geometrical Optics Question 161 English
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 : JEE Main 2019 (Online) 10th April Morning Slot Physics - Magnetic Effect of Current Question 150 English
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 : JEE Main 2019 (Online) 10th April Morning Slot Physics - Geometrical Optics Question 162 English
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 :
Answer
(A)
$${1 \over {\sqrt {\gamma g} }}{\tan ^{ - 1}}\left( {\sqrt {{\gamma \over g}} {V_0}} \right)$$
17
In a meter bridge experiment, the circuit diagram and the corresponding observation table are shown in figure JEE Main 2019 (Online) 10th April Morning Slot Physics - Current Electricity Question 239 English
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 : JEE Main 2019 (Online) 10th April Morning Slot Physics - Capacitor Question 110 English
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 : JEE Main 2019 (Online) 10th April Morning Slot Physics - Center of Mass and Collision Question 84 English
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 :
Answer
(A)
$$\sqrt {{2 \over m}} {\left( {{2 \over {15}}{{{q^2}} \over {4\pi {\varepsilon _0}a}}} \right)^{1/2}}$$
24
In the given circuit, an ideal voltmeter connected across the 10$$\Omega $$ resistance reads 2V. The internal resistance r, of each cell is: JEE Main 2019 (Online) 10th April Morning Slot Physics - Current Electricity Question 236 English
Answer
(C)
0.5 $$\Omega $$