Practice Questions

Q24.An EM wave from air enters a medium. The electric fields are E1 = E01ˆx cos[2πv( c −t)] → E2 = E02ˆx cos[k(2z −ct)]in medium, where the wave number k and frequency v refer to their values in the air. The medium is non-magnetic. If ϵr1 and ϵr2 refer to relative permittivities of air and medium respectively, which of the following options, is correct? ϵr1 1 ϵr1 (1) ϵr2 = 2 (2) ϵr2 = 4 ϵr1 ϵr1 1 (3) = 2 (4) = 4 ϵr2 ϵr2

Q25.Unpolarized light of intensity I is incident on a system of two polarizers, A followed by B. The intensity of emergent light is I . If a third the polarizer C is placed between A and B the intensity of emergent light is 2 reduced to I . The angle between the polarizers A and C is θ , then 3 (1) 2 41 (2) 1 41 cos θ = ( 3 ) cos θ = ( 3 ) (3) 1 21 (4) 2 21 cos θ = ( 3 ) cos θ = ( 3 )

Q25.Unpolarized light of intensity I passes through an ideal polariser A . Another identical polariser B is placed behind A . The intensity of light beyond B is found to be I . Now another identical polariser C is placed 2 between A and B. The intensity beyond B is now found to be I . The angle between polariser A and C is 8 (1) 60° (2) 0° (3) 30° (4) 45°

Q25.A plane polarized light is incident on a polariser with its pass axis making angle θ with x -axis, as shown in the figure. At four different values of θ, θ = 8∘, 38∘, 188∘ and 218∘ , the observed intensities are same. What is the angle between the direction of polarization and x -axis (1) 203∘ (2) 45∘ (3) 98∘ (4) 128∘

Q26.The energy required to remove the electron from a singly ionized Helium atom is 2.2 times the energy required to remove an electron from Helium atom. The total energy required to ionize the Helium atom completely is: (1) 20eV (2) 79eV (3) 109eV (4) 34eV JEE Main 2018 (15 Apr Shift 1 Online) JEE Main Previous Year Paper

Q26.The de-Broglie wavelength (λB) associated with the electron orbiting in the second excited state of hydrogen atom is related to that in the ground state (λG) by: (1) λB = 3λG (2) λB = 2λG (3) λB = λ G (4) λB = λ G 3 2

Q26.The energy required to remove the electron from a singly ionized Helium atom is 2. 2 times the energy required to remove an electron from helium atom. The total energy required to ionize the Helium atom completely is close to JEE Main 2018 (15 Apr) JEE Main Previous Year Paper (1) 34 eV (2) 20 eV (3) 79 eV (4) 109 eV

Q27.A solution containing active cobalt 6027Co having an activity of 0 .8 μCi and decay constant λ is injected in an animal's body. When 1 cm3 blood is drawn from the animal's body after 10 h of injection, the activity was found to be 300 dpm(decays per minute), then the total volume of blood in the animal's body is close to [1 Ci = 3 .7 ×1010 dps(decays per second) and at t = 10 h the value of e−λt = 0.84] (1) 4 L (2) 6 L (3) 5 L (4) 7 L

Q28.In a common emitter configuration with suitable bias, it is given that RL is the load resistance and RBE is small-signal dynamic resistance (input side). Then, voltage gain, current gain and power gain are given, respectively, by: β is current gain, IB , IC and IE are respectively base, collector, and emitter currents. (1) β RL , ΔIC , β2 RL (2) β RL , ΔIE , β2 RL RBE ΔIB RBE RBE ΔIB RBE (3) β2 RL , ΔIC , β RL (4) β2 RL , ΔIC , β2 RL RBE ΔIB RBE RBE ΔIE RBE

Q28.At some instant, a radioactive sample S1 having an activity 5μCi has twice the number of nuclei as another sample S2 which has an activity of 10μCi. The half lives of S1 and S2 are : (1) 4 : 1 (2) 1 : 4 (3) 1 : 2 (4) 2 : 1

Q28.If the series limit frequency of the Lyman series is VL, then the series limit frequency of the Pfund series is: (1) VL25 (2) 25 VL (3) 16 VL (4) VL16

Q28.In a common emitter configuration with suitable bias, it is given than RL is the load resistance and RBE is small signal dynamic resistance (input side). Then, voltage gain, current gain and power gain are given, respectively, by: [ β is current gain, IB, IC, IE are respectively base, collector and emitter currents] (1) β RL , ΔIE , β2 RL (2) β2 RL , ΔIC , β RL RBE ΔIB RBE RBE ΔIB RBE (3) β2 RL , ΔIC , β2 RL (4) β RL , ΔIC , β2 RL RBE ΔIE RBE RBE ΔIB RBE

Q28.An unstable heavy nucleus at rest breaks into two nuclei which move away with velocities in the ratio of 8 : 27 . The ratio of the radii of the nuclei (assumed to be spherical ) is: (1) 8 : 27 (2) 2 : 3 (3) 3 : 2 (4) 4 : 9 JEE Main 2018 (15 Apr Shift 2 Online) JEE Main Previous Year Paper

Q29.In the given circuit the current through zener diode is: (1) 3. 3 mA (2) 2. 5 mA (3) 5. 5 mA (4) 6. 7 mA

Q30.The carrier frequency of a transmitter is provided by a tank circuit of a coil of inductance 49μH and a capactiance of 2.5nF. It is modulated by an audio signal of 12kHz. The frequency range occupied by the side bands is: (1) 18kHz −30kHz (2) 63kHz −75kHz (3) 442kHz −466kHz (4) 13482kHz −13494kHz

Q30.In a screw gauge, 5 complete rotations of the screw cause it to move a linear distance of 0.25 cm. There are 100 circular scale divisions. The thickness of a wire measured by this screw gauge gives a reading of 4 main scale divisions and 30 circular scale divisions. Assuming negligible zero error, the thickness of the wire is: (1) 0.0430 cm (2) 0.3150 cm (3) 0.4300 cm (4) 0.2150 cm

Q31.A sample of NaClO3 is converted by heat to NaCl with a loss of 0. 16 g of oxygen. The residue is dissolved in water and precipitated as AgCl. The mass of AgCl (in g) obtained will be: (Given: Molar mass of AgCl = 143 .5 g mol−1 ) (1) 0. 35 (2) 0. 54 (3) 0. 41 (4) 0. 48

Q31.An unknown chlorohydrocarbon has 3.55 % of chlorine. If each molecule of the hydrocarbon has one chlorine atom only; chlorine atoms present in 1 g of chlorohydrocarbon are :(Atomic wt. of Cl = 35 .5 u; Avogadro constant = 6 .023 ×1023 mol–1 ) (1) 6.023 × 109 (2) 6.023 × 1023 (3) 6.023 × 1021 (4) 6.023 × 1020

Q31.For per gram of reactant, the maximum quantity of N2 gas is produced in which of the following thermal decomposition reactions? (Given: Atomic wt. : Cr = 52u, Ba = 137u ). (1) Ba(N3)2 (s) ⟶Ba(C) + 3 N2( g) (2) (NH4)2Cr2O7( s) ⟶ N2( g) + 4H2O(g) + Cr2O3( s) (3) 2NH3( g) ⟶N2( g) + 3H2( g) (4) 2NH4NO3( s) ⟶ 2 N2( g) + 4H2O(g) + O2( g)

Q31.The ratio of mass percent of C and H of an organic compound (CXHYOZ) is 6 : 1. If one molecule of the above compound (CXHYOZ) contains half as much oxygen as required to burn one molecule of compound CXHY completely to CO2 and H2O. The empirical formula of the compound CXHYOZ is (1) C2H4O3 (2) C3H6O3 (3) C2H4O (4) C3H4O2

Q31.A sample of NaClO3 is converted by heat to NaCl with a loss of 0.16 g of oxygen. The residue is dissolved in water and precipitated as AgCl. The mass of AgCl (in g) obtained will be: (Given: Molar mass of AgCl = 143.5 g mol−1 ) (1) 0.35 (2) 0.54 (3) 0.41 (4) 0.48

Q32.Which of the following statements is false? (1) Splitting of spectral lines in electrical field is (2) Frequency of emitted radiation from a black body called Stark effect goes from a higher wavelength to lower wavelength as the temperature increases (3) Photon has momentum as well as wavelength (4) Rydberg constant has unit of energy

Q32.The de-Broglie's wavelength of electron present in first Bohr orbit of ' H ' atom is: (1) 4 × 0.529Å (2) 2π × 0.529Å (3) 0.529 Å (4) 0.529Å 2π

Q32.According to molecular orbital theory, which of the following molecule will not be available? (1) H2−2 (2) He2+2 (3) He+2 (4) H−2

Q32.Ejection of the photoelectron from metal in the photoelectric effect experiment can be stopped by applying 0. 5 V , when the radiation of 250 nm is used. The work function of the metal is (1) 4 eV (2) 5. 5 eV (3) 4. 5 eV (4) 5 eV