JEE MAIN - Physics (2020 - 4th September Morning Slot)

1
A two point charges 4q and -q are fixed on the x-axis at x = $$ - {d \over 2}$$ and x = $${d \over 2}$$ respectively. If a third point charge 'q' is taken from the origin to x = d along the semicircle as shown in the figure, the energy of the charge will :
Risposta
(D)
decrease by $${{4{q^2}} \over {3\pi {\varepsilon _0}d}}$$
2
Dimensional formula for thermal conductivity is (here K denotes the temperature):
Risposta
(A)
MLT^–3K^–1
3
Starting from the origin at time t = 0, with initial velocity 5$$\widehat j$$ ms^-1 , a particle moves in the x-y plane with a constant acceleration of $$\left( {10\widehat i + 4\widehat j} \right)$$ ms^-2. At time t, its coordinates are (20 m, y₀ m). The values of t and y₀ are, respectively:
Risposta
(B)
2s and 18 m
4
Choose the correct option relating wave lengths of different parts of electromagnetic wave spectrum:
Risposta
(A)
$$\lambda $$_{radio waves} > $$\lambda $$_{micro waves} > $$\lambda $$_visible > $$\lambda $$_x-rays
5
Given figure shows few data points in a phot electric effect experiment for a certain metal. The minimum energy for ejection of electron from its surface is:
(Plancks constant h = 6.62 × 10^–34 J.s)
Risposta
(B)
2.27 eV
6
A air bubble of radius 1 cm in water has an upward acceleration 9.8 cm s^–2. The density of water is 1 gm cm^–3 and water offers negligible drag force on the bubble. The mass of the bubble is (g = 980 cm/s²).
Risposta
(D)
4.15 gm
7
A Tennis ball is released from a height h and after freely falling on a wooden floor it rebounds and reaches height $${h \over 2}$$. The velocity versus height of the ball during its motion may be represented graphically by :
(graph are drawn schematically and on not to scale)
Risposta
(C)
8
Particle A of mass m_A = $${m \over 2}$$ moving along the x-axis with velocity v₀ collides elastically with another particle B at rest having mass m_B = $${m \over 3}$$. If both particles move along the x-axis after the collision, the change $$\Delta $$$$\lambda $$ in de-Broglie wavlength of particle A, in terms of its de-Broglie wavelength ($$\lambda $$₀) before collision is :
Risposta
(D)
$$\Delta $$$$\lambda $$ = 4$$\lambda $$₀
9
A battery of 3.0 V is connected to a resistor dissipating 0.5 W of power. If the terminal voltage of the battery is 2.5 V, the power dissipated within the internal resistance is :
Risposta
(C)
0.10 W
10
Blocks of masses m, 2m, 4m and 8m are arranged in a line on a frictionless floor. Another block of mass m, moving with speed v along the same line (see figure) collides with mass m in perfectly inelastic manner. All the subsequent collisions are also perfectly inelastic. By the time the last block of mass 8m starts moving the total energy loss is p% of the original energy. Value of 'p' is close to :
Risposta
(D)
94
11
For a transverse wave travelling along a straight line, the distance between two peaks (crests) is 5 m, while the distance between one crest and one trough is 1.5 m. The possible wavelengths (in m) of the are :
Risposta
(B)
$${1 \over 1},{1 \over 3},{1 \over 5},$$ .....
12
A small bar magnet is moved through a coil at constant speed from one end to the other. Which of the following series of observations will be seen on the galvanometer G attached across the coil?
Three positions shown describe :
(a) the magnet's entry
(b) magnet is completely inside and
(c) magnet's exit.
Risposta
(C)
13
A wire A, bent in the shape of an arc of a circle, carrying a current of 2 A and having radius 2 cm and another wire B, also bent in the shape of arc of a circle, carrying a current of 3 A and having radius of 4 cm, are placed as shown in the figure. The ratio of the magnetic fields due to the wires A and B at the common centre O is :
Risposta
(D)
6 : 5

Match the $${{{C_P}} \over {{C_V}}}$$ ratio for ideal gases with different type of molecules :

Molecule Type	C_P/C_V
(A) Monatomic	(I) 7/5
(B) Diatomic rigid molecules	(II) 9/7
(C) Diatomic non-rigid molecules	(III) 4/3
(D) Triatomic rigid molecules	(IV) 5/3

Risposta

(C)

(A)-(IV), (B)-(I), (C)-(II), (D)-(III)

15
A beam of plane polarised light of large
cross-sectional area and uniform intensity
of 3.3 Wm^-2 falls normally on a
polariser (cross sectional area 3 $$ \times $$ 10^-4 m²) which
rotates about its axis with an angular speed
of 31.4 rad/s. The energy of light passing through
the polariser per revolution, is close to :
Risposta
(B)
1.0 $$ \times $$ 10^-4 J
16
The specific heat of water
= 4200 J kg^-1K^-1 and the latent heat of
ice = 3.4 $$ \times $$ 10⁵ J kg^–1. 100 grams of ice at
0^oC is placed in 200 g of water at 25^oC. The
amount of ice that will melt as the temperature
of water reaches 0^oC is close to (in grams) :
Risposta
(B)
61.7
17
Take the breakdown voltage of the
zener diode used in the given circuit as 6V.
For the input voltage shown in figure below,
the time variation of the output voltage is:
(Graphs drawn are schematic and not to scale)
Risposta
(C)
18
A small bar magnet placed with its axis
at 30^o with an external field of 0.06 T
experiences a torque of 0.018 Nm. The
minimum work required to rotate it from its
stable to unstable equilibrium position is :
Risposta
(C)
7.2 $$ \times $$ 10^-2 J
19
Two charged thin infinite plane sheets of
uniform surface charge density $${\sigma _ + }$$ and $${\sigma _ - }$$,
where |$${\sigma _ + }$$| > |$${\sigma _ - }$$|, intersect at right angle.
Which of the following best represents the
electric field lines for this system :
Risposta
(B)
20
In a compound microscope, the magnified virtual image is formed at a distance of 25 cm from the eye-piece. The focal length of its objective lens is 1 cm. If the magnification is 100 and the tube length of the microscope is 20 cm, then the focal length of the eye-piece lens (in cm) is __________.
Risposta
6.25
21
A circular disc of mass M and radius R is rotating about its axis with angular speed $${\omega _1}$$ . If another stationary disc having radius $${R \over 2}$$ and same mass M is droped co-axially on to the rotating disc. Gradually both discs attain constant angular speed $${\omega _2}$$ the energy lost in the process is p% of the initial energy. Value of p is __________.
Risposta
20
22
A closed vessel contains 0.1 mole of a monoatomic ideal gas at 200 K. If 0.05 mole of the same gas at 400 K is added to it, the final equilibrium temperature (in K) of the gas in the vessel will be close to _______.
Risposta
266
23
On the x-axis and at a distance x from the origin, the gravitational field due a mass distribution is given by $${{Ax} \over {{{\left( {{x^2} + {a^2}} \right)}^{3/2}}}}$$ in the x-direction. The magnitude of gravitational potential on the x-axis at a distance x, taking its value to be zero at infinity, is:
Risposta
(C)
$${A \over {{{\left( {{x^2} + {a^2}} \right)}^{1/2}}}}$$