JEE MAIN - Physics (2020 - 2nd September Morning Slot)

• 1

  The least count of the main scale of a vernier callipers is 1 mm. Its vernier scale is divided into 10 divisions and coincide with 9 divisions of the main scale. When jaws are touching each other, the 7^th division of vernier scale coincides with a division of main scale and the zero of vernier scale is lying right side of the zero of main scale. When this vernier is used to measure length of a cylinder the zero of the vernier scale between 3.1 cm and 3.2 cm and 4^th VSD coincides with a main scale division. The length of the cylinder is : (VSD is vernier scale division)

  پاسخ دهید

  (C)

  3.07 cm
• 2

  A spherical mirror is obtained as shown in the figure from a hollow glass sphere. If an object is positioned in front of the mirror, what will be the nature and magnification of the image of the object?
  (Figure drawn as schematic and not to scale)

  پاسخ دهید

  (A)

  Inverted, real and unmagnified
• 3

  In a reactor, 2 kg of ₉₂U²³⁵ fuel is fully used up in 30 days. The energy released per fission is 200 MeV. Given that the Avogadro number, N = 6.023 $$ \times $$ 10²⁶ per kilo mole and 1 eV = 1.6 × 10^–19 J. The power output of the reactor is close to

  پاسخ دهید

  (B)

  60 MW
• 4

  Consider four conducting materials copper, tungsten, mercury and aluminium with resistivity $$\rho $$_C, $$\rho $$_T, $$\rho $$_M and $$\rho $$_A respectively. Then :

  پاسخ دهید

  (B)

  $$\rho $$_M > $$\rho $$_A > $$\rho $$_C
• 5

  A particle of mass m with an initial velocity $$u\widehat i$$ collides perfectly elastically with a mass 3 m at rest. It moves with a velocity $$v\widehat j$$ after collision, then, v is given by :

  پاسخ دهید

  (C)

  $$v = {u \over {\sqrt 2 }}$$
• 6

  A gas mixture consists of 3 moles of oxygen and 5 moles of argon at temperature T. Assuming the gases to be ideal and the oxygen bond to be rigid, the total internal energy (in units of RT) of the mixture is :

  پاسخ دهید

  (C)

  15
• 7

  The mass density of a spherical galaxy varies as $${K \over r}$$ over a large distance ‘r’ from its centre. In that region, a small star is in a circular orbit of radius R. Then the period of revolution, T depends on R as :

  پاسخ دهید

  (A)

  T² $$ \propto $$ R
• 8

  Train A and train B are running on parallel tracks in the opposite directions with speeds of 36 km/hour and 72 km/hour, respectively. A person is walking in train A in the direction opposite to its motion with a speed of 1.8 km/ hour. Speed (in ms^–1) of this person as observed from train B will be close to :
  (take the distance between the tracks as negligible)

  پاسخ دهید

  (B)

  29.5 ms^–1
• 9

  If speed V, area A and force F are chosen as fundamental units, then the dimension of Young’s modulus will be

  پاسخ دهید

  (A)

  FA^–1V⁰
• 10

  
  A small block starts slipping down from a point B on an inclined plane AB, which is making an angle $$\theta $$ with the horizontal section BC is smooth and the remaining section CA is rough with a coefficient of friction $$\mu $$. It is found that the block comes to rest as it reaches the bottom (point A) of the inclined plane. If BC = 2AC, the coefficient of friction is given by $$\mu $$ = ktan $$\theta $$ . The value of k is _________.

  پاسخ دهید

  3
• 11

  A uniform cylinder of mass M and radius R is to be pulled over a step of height a (a < R) by applying a force F at its centre ‘O’ perpendicular to the plane through the axes of the cylinder on the edge of the step (see figure). The minimum value of F required is :

  پاسخ دهید

  (A)

  $$Mg\sqrt {1 - {{\left( {{{R - a} \over R}} \right)}^2}} $$
• 12

  
  Shown in the figure is rigid and uniform one meter long rod AB held in horizontal position by two strings tied to its ends and attached to the ceiling. The rod is of mass ‘m’ and has another weight of mass 2 m hung at a distance of 75 cm from A. The tension in the string at A is :

  پاسخ دهید

  (D)

  1 mg
• 13

  A bead of mass m stays at point P(a, b) on a wire bent in the shape of a parabola y = 4Cx² and rotating with angular speed $$\omega $$ (see figure). The value of $$\omega $$ is (neglect friction) :

  پاسخ دهید

  (A)

  $$2\sqrt {2gC} $$
• 14

  Two identical strings X and Z made of same material have tension T_X and T_Z in them. If their fundamental frequencies are 450 Hz and 300 Hz, respectively, then the ratio T_X/T_Z is

  پاسخ دهید

  (A)

  2.25
• 15

  Interference fringes are observed on a screen by illuminating two thin slits 1 mm apart with a light source ($$\lambda $$ = 632.8 nm). The distance between the screen and the slits is 100 cm. If a bright fringe is observed on a screen at a distance of 1.27 mm from the central bright fringe, then the path difference between the waves, which are reaching this point from the slits is close is

  پاسخ دهید

  (A)

  1.27 $$\mu $$m
• 16

  A cylindrical vessel containing a liquid is rotated about its axis so that the liquid rises at its sides as shown in the figure. The radius of vessel is 5 cm and the angular speed of rotation is $$\omega $$ rad s^–1. The difference in the height, h (in cm) of liquid at the centre of vessel and at the side will be :

  پاسخ دهید

  (C)

  $${{25{\omega ^2}} \over {2g}}$$
• 17

  A charged particle (mass m and charge q)
  moves along X-axis with velocity V₀. When it
  passes through the origin it enters a region having uniform electric field
  $$\overrightarrow E = - E\widehat j$$ which extends upto x = d.
  Equation of path of electron in the region x > d is

  پاسخ دهید

  (B)

  y = $${{qEd} \over {mV_0^2}}\left( {{d \over 2} - x} \right)$$
• 18

  A plane electromagnetic wave, has
  frequency of 2.0 $$ \times $$ 10¹⁰ Hz and its energy density is 1.02 $$ \times $$ 10^–8 J/m³ in vacuum. The amplitude of the magnetic field of the wave is close to
  ( $${1 \over {4\pi {\varepsilon _0}}} = 9 \times {10^9}{{N{m^2}} \over {{C^2}}}$$ and speed of light
  = 3 $$ \times $$ 10⁸ ms^–1)

  پاسخ دهید

  (C)

  160 nT
• 19

  A 5 $$\mu $$F capacitor is charged fully by a 220 V supply. It is then disconnected from the supply and is connected in series to another uncharged 2.5 $$\mu $$F capacitor. If the energy change during the charge redistribution is $${X \over {100}}J$$ then value of X to the nearest integer is _____.

  پاسخ دهید

  4
• 20

  A circular coil of radius 10 cm is placed in a uniform magnetic field of 3.0 $$ \times $$ 10^–5 T with its plane perpendicular to the field initially. It is rotated at constant angular speed about an axis along the diameter of coil and perpendicular to magnetic field so that it undergoes half of rotation in 0.2 s. The maximum value of EMF induced (in $$\mu $$V) in the coil will be close to the integer _______.

  پاسخ دهید

  15
• 21

  When radiation of wavelength $$\lambda $$ is used to illuminate a metallic surface, the stopping potential is V. When the same surface is illuminated with radiation of wavelength 3$$\lambda $$, the stopping potential is $${V \over 4}$$. If the threshold wavelength for the metallic surface is n$$\lambda $$ then value of n will be __________.

  پاسخ دهید

  9
• 22

  A beam of protons with speed 4 × 10⁵ ms^–1 enters a uniform magnetic field of 0.3 T at an angle of 60° to the magnetic field. The pitch of the resulting helical path of protons is close to :
  (Mass of the proton = 1.67 $$ \times $$ 10^–27 kg, charge
  of the proton = 1.69 $$ \times $$ 10^–19 C)

  پاسخ دهید

  (D)

  4 cm
• 23

  An engine takes in 5 moles of air at 20^oC and 1 atm, and compresses it adiabatically to 1/10^th of the original volume. Assuming air to be a diatomic ideal gas made up of rigid molecules, the change in its internal energy during this process comes out to be X kJ. The value of X to the nearest integer is________.

  پاسخ دهید

  46