JEE MAIN - Physics (2019 - 12th January Evening Slot)

1
A load of mass M kg is suspended from a steel wire of length 2m and radius 1.0 mm in Searle's apparatus experiment. The increase in length produced in the wire is 4.0 mm. Now the load is fully immersed in a liquid of relative density 2. The relative density of the material of load is 8.

The new value of increase in length of the steel wire is:
پاسخ دهید
(C)
3.0 mm
2
In the circuit shown, find C if the effective capacitance of the whole circuit is to be 0.5 $$\mu $$F. All values in the circuit are in $$\mu $$F.

پاسخ دهید
(B)
$${7 \over 11}\mu F$$
3
Two particles A, B are moving on two concentric circles of radii R₁ and R₂ with equal angular speed $$\omega $$. At t = 0, their positions and direction of motion are shown in the figure. :

The relative velocity $${\overrightarrow V _A} - {\overrightarrow V _B}$$ at t = $${\pi \over {2\omega }}$$ is given by :
پاسخ دهید
(B)
$$\omega \left( {{R_2} - {R_1}} \right)\,\widehat i$$
4
A soap bubble, blown by a mechanical pump at the mouth of a tube, increases in volume, with time, at a constant rate. The graph that correctly depicts the time dependence of pressure inside the bubble is given by :
پاسخ دهید
(B)
5
The mean intensity of radiation on the surface of the Sun is about 10⁸ W/m² . The rms value of the corresponding magnetic field is closet to :
پاسخ دهید
(C)
10^$$-$$4 T
6
A 10 m long horizontal wire extends from North East to South West. It is falling with a speed of 5.0 ms^–1, at right angles to the horizontal component of the earth's magnetic field of 0.3 $$ \times $$ 10^–4 Wb/m². The value of the induced emf in wire is :
پاسخ دهید
(D)
1.1 $$ \times $$ 10^–3 V
7
A resonance tube is old and has jagged end. It is still used in the laboratory to determine velocity of sound in air. A tuning fork of frequency 512 Hz produces first resonance when the tube is filled with water to a mark 11 cm below a reference mark, near the open end of the tube. The experiment is repeated with another fork of frequency 256 Hz which produces first resonance when water reaches a mark 27 cm below the reference mark. The velocity of sound in air, obtained in the experiment, is close to :
پاسخ دهید
(B)
328 ms^–1
8
An alpha-particle of mass m suffers 1-dimensional elastic collision with a nucleus at rest of unknown mass. It is scattered directly backwards losing, 64% of its initial kinetic energy. The mass of the nucleus is
پاسخ دهید
(B)
4m
9
A vertical closed cylinder is separated into two parts by a frictionless piston of mass m and of negligible thickness. The piston is free to move along the length of the cylinder. The length of the cylinder above the piston is $$\ell $$₁, and that below the piston is $$\ell $$₂, such that $$\ell $$₁ > $$\ell $$₂. Each part of the cylinder contains n moles of an ideal gas at equal temperature T. If the piston is stationary, its mass, m, will be given by :
(R is universal gas constant and g is the acceleration due to gravity)
پاسخ دهید
(A)
$${{nRT} \over g}\left[ {{{{\ell _1} - {\ell _2}} \over {{\ell _1}{\ell _2}}}} \right]$$
10
A parallel plate capacitor with plates of area 1 m² each, are at a separation of 0.1 m. If the electric field between the plates is 100 N/C, the magnitude of charge on each plate is :

(Take $$\varepsilon $$₀ = 8.85 $$ \times $$ 10^$$-$$12 $${{{C^2}} \over {N - {m^2}}}$$)
پاسخ دهید
(B)
8.85 $$ \times $$ 10^–10 C
11
When a certain photosensitive surface is illuminated with monochromatic light of frequency v, the stopping potential for the current is –V₀/2. When the surface is illuminated by monochromatic light of frequency v/2, the stopping potential is – V₀. The threshold frequency for photoelectric emission is :
پاسخ دهید
(C)
$${{3v} \over 2}$$
12
A paramagnetic material has 10²⁸ atoms/m³. Its magnetic susceptibility at temperature 350 K is 2.8 $$ \times $$ 10^–4. Its susceptibility at 300 K is :
پاسخ دهید
(D)
3.267 $$ \times $$ 10^$$-$$4
13
In a Frank-Hertz experiment, an electron of energy 5.6 eV passes through mercury vapour and emerges with an energy 0.7 eV. The minimum wavelength of photons emitted by mercury atoms is close to :
پاسخ دهید
(B)
250 nm
14
The moment of inertia of a solid sphere, about an axis parallel to its diameter and at a distance of x from it, is 'I(x)'. Which one of the graphs represents the variation of I(x) with x correctly ?
پاسخ دهید
(C)
15
In the given circuit diagram, the currents, I₁ = – 0.3 A, I₄ = 0.8 A and I₅ = 0.4 A, are flowing as shown. The currents I₂, I₃ and I₆, respectively, are :

پاسخ دهید
(D)
1.1 A, 0.4 A, 0.4 A
16
A plano-convex lens (focal length f₂, refractive index $$\mu $$₂, radius of curvature R) fits exactly into a plano-concave lens (focal length f₁, refractive index $$\mu $$₁, radius of curvature R). Their plane surfaces are parallel to each other. Then, the focal length of the combination will be :
پاسخ دهید
(C)
$${R \over {{\mu _2} - {\mu _1}}}$$
17
A block kept on a rough inclined plane, as shown in the figure, remains at rest upto a maximum force 2 N down the inclined plane. The maximum external force up the inclined plane that does not move the block is 10 N. The coefficient of static friction between the block and the plane is : [Take g = 10 m/s²]

پاسخ دهید
(C)
$${{\sqrt 3 } \over 2}$$
18
Let $$\ell $$, r, C and V represent inductance, resistance, capacitance and voltage, respectively. The dimension of $${\ell \over {rCV}}$$ in SI units will be :
پاسخ دهید
(A)
[A^–1]
19
A simple harmonic motion is represented by :

y = 5 (sin 3 $$\pi $$ t + $$\sqrt 3 $$ cos 3 $$\pi $$t) cm

The amplitude and time period of the motion are :
پاسخ دهید
(D)
10 cm, $${2 \over 3}$$ s
20
Two satellites, A and B, have masses m and 2m respectively. A is in a circular orbit of radius R, and B is in a circular orbit of radius 2R around the earth. The ratio of their kinetic energies, T_A/T_B, is ;
پاسخ دهید
(D)
1
21
A galvanometer, whose resistance is 50 ohm, has 25 divisions in it. When a current of 4 $$ \times $$ 10^–4 A passes through it, its needle ( pointer) deflects by one division. To use this galvanometer as a voltmeter of range 2.5 V, it should be connected to a resistance of :
پاسخ دهید
(A)
200 ohm
22
A particle of mass 20 g is released with an initial velocity 5 m/s along the curve from the point A, as shown in the figure. The point A is at height h from point B. The particle slides along the frictionless surface. when the particle reaches point b, its angular momentum about O will be :
(Take g = 10 m/s²)

پاسخ دهید
(A)
6 kg-m²/s
23
An ideal gas is enclosed in a cylinder at pressure of 2 atm and temperature 300 K. The mean time between two successive collisions is 6 $$ \times $$ 10^–8 s. If the pressure is doubled and temperature is increased to 500 K, the mean time between two successive collisions will be close to
پاسخ دهید
(B)
4 $$ \times $$ 10^$$-$$8 s
24
In the circuit shown, find C if the effective capacitance of the whole circuit is to be 0.5 $$\mu $$F. All values in the circuit are in $$\mu $$F.

پاسخ دهید
(B)
$${7 \over 11}\mu F$$
25
Formation of real image using a biconvex lens is shown below :

If the whole set up is immersed in water without disturbing the object and the screen positions, what will one observe on the screen ?
پاسخ دهید
(A)
Image disappears
26
In the above circuit, C = $${{\sqrt 3 } \over 2}$$$$\mu $$F, R₂ = 20 $$\Omega $$, L = $${{\sqrt 3 } \over {10}}$$ H and R₁ = 10 $$\Omega $$. Current in L-R₁ path is I₁ and in C-R₂ path it is I₂ . The voltage of A.C. source is given by, V = 200 $${\sqrt 2 }$$ sin (100 t) volts . The phase difference between I₁ and I₂ is :

پاسخ دهید
(C)
30^o
27
A soap bubble, blown by a mechanical pump at the mouth of a tube, increases in volume, with time, at a constant rate. The graph that correctly depicts the time dependence of pressure inside the bubble is given by :
پاسخ دهید
(B)