JEE MAIN - Physics (2018 - 16th April Morning Slot)

• 1

  A heating element has a resistance of 100 $$\Omega $$ at room temperature. When it is connected to a supply of 220 V, a steady current of 2 A passes in it and temperature is 500^oC more than room temperature. what is the temperature coefficient of resistance of the heating element ?

  Odpověď

  (D)

  2 $$ \times $$ 10^{$$-$$4 o}C^$$-$$1
• 2

  Both the nucleus and the atom of some element arein their respective first excited states. They get de-excted by emitting photons of wavelengths ^{$$\lambda $$}N, ^{$$\lambda $$}A respectively. The ratio $${{{}^\lambda N} \over {{}^\lambda A}}$$is closest to :

  Odpověď

  (A)

  10^$$-$$6
• 3

  The de-Broglie wavelength ($$\lambda $$_B) associated with the electron orbiting in the second excited state of hydrogen atom is related to that in the ground state ($$\lambda $$_G) by :

  Odpověď

  (B)

  $$\lambda $$_B = 3$$\lambda $$_G
• 4

  Unpolarized light of intensity I is incident on a system of two polarizers, A followed by B. The intensity of emergent light is I/2. If a third polarizer C is placed between A and B, the intensity of emergent light is reduced to I/3. The angle between the polarizers A and C is $$\theta $$. Then :

  Odpověď

  (B)

  cos$$\theta $$ = $${\left( {{2 \over 3}} \right)^{{\raise0.5ex\hbox{$\scriptstyle 1$} \kern-0.1em/\kern-0.15em \lower0.25ex\hbox{$\scriptstyle 4$}}}}$$
• 5

  A ray of light is incident at an angle of 60^o on one face of a prism of angle 30^o. The emergent ray of light makes an angle of 30^o with incident ray. The angle made by the emergent ray with second face of prism will be :

  Odpověď

  (B)

  90^o
• 6

  A charge q is spread uniformly over an insulated loop of radius r. If it is rotated with an angular velocity $$\omega $$ with resect to normal axis then the magnetic moment of the loop is :

  Odpověď

  (D)

  $${1 \over 2}$$ q $$\omega $$r²
• 7

  A plane electromagnetic wave of wavelength $$\lambda $$ has an intensity I. It is propagatting along the positive Y-direction. The allowed expressions for the electric and magnetic fields are givn by :

  Odpověď

  (A)

  
• 8

  A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns, giving the output power at 230 V. If the current in the primary of the transformer is 5 A, and its efficiency is 90%, the output current would be ;

  Odpověď

  (B)

  45 A
• 9

  A coil of cross-sectional area A having n turns is placed in a uniform magnetic field B. When it is rotated with an angular velocity $$\omega ,$$ the maxium e.m.f. induced in the coil will be:

  Odpověď

  (C)

  nBA$$\omega $$
• 10

  A galvanometer with its coil resistance 25 $$\Omega $$ requires a current of 1 mA for its full deflection. In order to construct an ammeter to read upto a current of 2 A, the approximate value of the shunt resistance should be :

  Odpověď

  (B)

  $$1.25 \times {10^{ - 2}}\Omega $$
• 11

  Two identical conducting spheres A and B, carry equal charge. They are separated by a distance much larger than their diameters, and the force between theis F. A third identical conducting sphere, C, is uncharged. Sphere C is first touhed to A, then to B, and then removed. As a result, the force between A and B would be equal to :

  Odpověď

  (C)

  $${{3F} \over 8}$$
• 12

  Two moles of helium are mixed with n moles of hydrogen. If $${{Cp} \over {Cv}} = {3 \over 2}$$ for the mixture, then the value of n is :

  Odpověď

  (C)

  2
• 13

  A particle executes simple harmonic motion and is located at x = a, b and c at times t₀, 2t₀ and 3t₀ respectively. The freqquency of the oscillation is :

  Odpověď

  (A)

  $${1 \over {2\,\pi \,{t_0}}}{\cos ^{ - 1}}\left( {{{a + c} \over {2b}}} \right)$$
• 14

  A small soap bubble of radius 4 cm is trapped inside another bubble of radius 6 cm without any contact. Let P₂ be the pressure inside the inner bubble and P₀, the pressure outside the outer bubble. Radius of another bubble with pressure difference P₂ $$-$$ P₀ between its inside and outside would be :

  Odpověď

  (B)

  2.4 cm
• 15

  An oscillator of mass M is at rest in its equilibrium position in a potential
  V = $${1 \over 2}$$ k(x $$-$$ X)². A particle of mass m comes from right with speed u and collides completely inelastically with M and sticks to it. This process repeats every time the oscillator crosses its equilibrium position. The amplitude of oscillations after 13 collisions is : (M = 10, m = 5, u = 1, k = 1)

  Odpověď

  (A)

  $${1 \over {\sqrt 3 }}$$
• 16

  Suppose that the angular velocity of rotation of earth is increased. Then, as a consequence :

  Odpověď

  (D)

  Except at poles, weight of the object on the earth will decrease.
• 17

  The relative uncertainly in the period of a satellite orbiting around the earth is 10^-2. If the relative uncertainty in the radius of the orbit is negligible, the relative uncertainty in the mass of the earth is :

  Odpověď

  (B)

  2 $$ \times $$ 10^$$-$$2
• 18

  A body of mass m starts moving from rest along x-axis so that its velocity varies as $$\upsilon = a\sqrt s $$ where a is a constant and s is the distance covered by the body. The total work done by all the forces acting on the body in the first t seconds after the start of the motion is :

  Odpověď

  (A)

  $${1 \over 8}\,$$ m a⁴ t²
• 19

  Two particles of the same mass m are moving in circular orbits because of force, given by $$F\left( r \right) = {{ - 16} \over r} - {r^3}$$
  
  The first particle is at a distance r = 1, and the second, at r = 4. The best estimate for the ratio of kinetic energies of the first and the second particle is closest to :

  Odpověď

  (A)

  $$6 \times {10^{ - 2}}$$
• 20

  Let $$\overrightarrow A $$ = $$\left( {\widehat i + \widehat j} \right)$$ and, $$\overrightarrow B = \left( {2\widehat i - \widehat j} \right).$$ The magnitude of a coplanar vector $$\overrightarrow C $$ such that $$\overrightarrow A .\overrightarrow C = \overrightarrow B .\overrightarrow C = \overrightarrow A .\overrightarrow B ,$$ is given by :

  Odpověď

  (B)

  $$\sqrt {{{5} \over 9}} $$
• 21

  The percentage errors in quantities P, Q, R and S are 0.5%, 1%, 3% and 1.5% respectively in the measurement of a physical quantity A = $${{{P^3}{Q^2}} \over {\sqrt R S}}.$$
  
  The maximum percentage error in the value of A will be :

  Odpověď

  (D)

  6.5%
• 22

  A thin circular disk is in the xy plane as shown in the figure. The ratio of its moment of inertia about z and z' axes will be :
  
  

  Odpověď

  (A)

  1 : 3
• 23

  In the following circuit, the switch S is closed at t = 0. The charge on the capacitor C₁ as a function of time will be given by $$\left( {{C_{eq}} = {{{C_1}{C_2}} \over {{C_1} + {C_2}}}} \right)$$
  
  

  Odpověď

  (C)

  $${C_{eq}}E\left[ {1 - \exp \left( { - t/R{C_{eq}}} \right)} \right]$$
• 24

  One mole of an ideal monoatomic gas is taken along the path ABCA as show in the PV diagram. The maximum temperature attained by the gas along the path BC is given by :
  
  

  Odpověď

  (B)

  $${{25} \over {8}}\,{{{P_o}{V_o}} \over R}$$
• 25

  In the given circuit, the current through zener diode is :
  
  

  Odpověď

  (D)

  3.3 mA
• 26

  In a circuit for finding the resistance of a galvanometer by half deflection method, a 6 V battery and a high resistance of 11 k$$\Omega $$ are used. The figure of merit of the galvanometer is 60 $$\mu A/$$division. In the absence of shunt resistance, the galvanometer produces a deflection of $$\theta $$ = 9 divisions when current flows in the circuit. The value of the shunt resistance that can cause the deflection of $$\theta /2,$$ is closest to :

  Odpověď

  (D)

  110 $$\Omega $$
• 27

  The end correction of a resonance column is 1 cm. If the shortest length resonating with the tunning fork is 10 cm, the next resonating length should be :

  Odpověď

  (B)

  32 cm