Practice Questions

Q22.An LCR circuit is equivalent to a damped pendulum. In an LCR circuit the capacitor is charged to Q0 and then connected to the L and R as shown below: If a student plots graphs of the square of maximum charge (Q2Max) on the capacitor with time (t) for two different values L1 and L2(L1 > L2) of L then which of the following represents this graph correctly? (plots are schematic and not drawn to scale) JEE Main 2015 (04 Apr) JEE Main Previous Year Paper (1) (2) (3) (4)

Q23.An inductor (L = 0.03 H) and a resistor (R = 0.15 kΩ) are connected in series to a battery of 15 V E.M.F. in a circuit shown below. The key K1 has been kept closed for a long time. Then at t = 0, K1 is opened and key K2 is closed simultaneously. At t = 1 ms , the current in the circuit will be : (Take, e5 ≈150) (1) 0. 67 mA (2) 100 mA (3) 67 mA (4) 6. 7 mA

Q24.A red LED emits light at 0. 1 watt uniformly around it. The amplitude of the electric field of the light at a distance of 1 m from the diode is: (1) 7. 75 V m−1 (2) 1. 73 V m−1 (3) 2. 45 V m−1 (4) 5. 48 V m−1

Q24.A telescope has an objective lens of focal length 150 cm and an eyepiece of focal length 5 cm. If a 50 m tall tower at a distance of 1 km is observed through this telescope in a normal setting, the angle formed by the image of the tower is θ, then θ is close to (1) 30° (2) 15° (3) 1° (4) 86°

Q24.For plane electromagnetic waves propagating in the +z-direction, which one of the following combinations → → gives the correct possible direction for E and B field respectively? + (1) (ˆi 2ˆj) and (2ˆi −j) (2) (−2ˆi −3ˆj) and (3ˆi −2ˆj) + + + (3) (2ˆi 3ˆj) and (ˆi 2ˆj) (4) (3ˆi 4ˆj) and (4ˆi −3ˆj)

Q25.You are asked to design a shaving mirror assuming that a person keeps it at 10 cm from his face and views the magnified image of the face at the closest comfortable distance of 25 cm. The radius of curvature of the mirror would then be: (1) 24 cm (2) 30 cm (3) 60 cm (4) −24 cm

Q25.A thin convex lens of focal length f is put on a plane mirror as shown in the figure. When an object is kept at a distance a from the lens-mirror combination, its image is formed at a distance a3 in front of the combination. JEE Main 2015 (11 Apr Online) JEE Main Previous Year Paper The value of a is: (1) 2f (2) 32 f (3) 3f (4) f

Q26.In a Young's double slit experiment with light of wavelength λ, the separation of slits is d and distance of screen is D such that D ≫d ≫λ . If the Fringe width is β , the distance from point of maximum intensity to the point where intensity falls to half of the maximum intensity on either side is: (1) β (2) β 4 3 (3) β (4) β 6 2

Q26.On a hot summer night, the refractive index of air is the smallest near the ground and increases with a height from the ground. When a light beam is directed horizontally, the Huygens' principle leads us to conclude that as it travels, the light beam, (1) bends upward. (2) becomes narrower. (3) goes horizontally without any deflection. (4) bends downward.

Q26.A parallel beam of electrons travelling in x - direction falls on a slit of width d (see figure). If after passing the slit, an electron acquires momentum py in the y - direction then for a majority of electrons passing through the JEE Main 2015 (10 Apr Online) JEE Main Previous Year Paper slit (h is Planck's constant): (1) |py|d < h (2) |py|d > h (3) |py|d ≃h (4) |py|d >> h

Q27.Unpolarized light of intensity I0 is incident on surface of a block of glass at Brewster's angle. In that case, which one of the following statements is true? (1) transmitted light is partially polarized with (2) transmitted light is completely polarized with intensity I0 intensity less than I0 2 2 (3) reflected light is partially polarized with intensity(4) reflected light is completely polarized with I0 intensity less than I0 2 2

Q27.Assuming that the human pupil has a radius of 0. 25 cm and a comfortable viewing distance of 25 cm. The minimum separation between two point objects that the human eye can resolve for the light of wavelength 500 nm is (1) 300 μm (2) 1 μm (3) 30 μm (4) 100 μm

Q28.The de-Broglie wavelength associated with the electron in the n = 4 level is: (1) Half of the de-Broglie wavelength of the electron (2) Four times the de-Broglie wavelength of the in the ground state electron in the ground state (3) 1 th of the de-Broglie wavelength of the electron (4) Two times the de-Broglie wavelength of the 4 in the ground state electron in the ground state

Q29.As an electron makes a transition from an excited state to the ground state of a hydrogen-like atom/ion (1) kinetic energy and total energy decrease but (2) its kinetic energy increases but potential energy potential energy increases and total energy decrease (3) kinetic energy, potential energy and total energy (4) kinetic energy decreases, potential energy decrease increases but total energy remains same

Q29.Let Nβ be the number of β particle emitted by 1 gram of Na24 radioactive nuclei having a half life of 15 h. In 7. 5 h, the number Nβ is close to [NA = 6 .023 ×1023 mole−1] (1) 1.75 × 1022 (2) 6.2 × 1021 (3) 7.5 × 1021 (4) 1.25 × 1022

Q30.The value of the resistor, RS , needed in the DC voltage regulator circuit shown here, equals: (1) (Vi+VL) (2) (Vi−VL) (n+1)IL n IL (3) (Vi+VL) (4) (Vi−VL) n IL (n+1)IL JEE Main 2015 (11 Apr Online) JEE Main Previous Year Paper

Q30.Diameter of a steel ball is measured using a Vernier calipers which has divisions of 0.1 cm on its main scale (MS) and 10 divisions of its Vernier scale (VS) match 9 divisions on the main scale. Three such measurements for a ball are given as: S.No. MS (cm) VS divisions 1. 0.5 8 2. 0.5 4 3. 0.5 6 If the zero error is - 0.03 cm, then mean corrected diameter is: (1) 0. 53 cm (2) 0. 56 cm (3) 0. 59 cm (4) 0. 52 cm

Q31.A sample of a hydrate of barium chloride weighing 61 g was heated until all the water of hydration is removed. The dried sample weighed 52 g. The formula of the hydrated salt is: (atomic mass, Ba = 137 amu, Cl = 35.5 amu) (1) BaCl2 ⋅H2O (2) BaCl2 ⋅3H2O (3) BaCl2 ⋅4H2O (4) BaCl2 ⋅2H2O JEE Main 2015 (10 Apr Online) JEE Main Previous Year Paper

Q31.The molecular formula of a commercial resin used for exchanging ions in water softening is C8H7SO3Na (molecular weight = 206). What would be the maximum uptake of Ca2+ ions by the resin if expressed in mol per gm? (1) 1 (2) 1 412 103 (3) 1 (4) 2 206 309

Q31.A 2 V battery is connected across AB as shown in the figure. The value of the current supplied by the battery when in first case battery's positive terminal is connected to A and in second case when positive terminal of battery is connected to B will respectively be: (1) 0.2 A and 0.1 A (2) 0.1 A and 0.2 A (3) 0.2 A and 0.4 A (4) 0.4 A and 0.2 A

Q32.In the following reaction: A + 2B + 3C ⇌AB2C3 6. 0 g of A, 6.0 × 1023 atoms of B and 0. 036 mol of C reacted and formed 4. 8 g of compound AB2C3 . If the atomic mass of A and C are 60 and 80 amu, respectively. What is the atomic mass of B in amu ? (Avogadro number = 6 × 1023 ) (1) 40 amu (2) 60 amu (3) 70 amu (4) 50 amu

Q33.The ionic radii (in Å) of N3−, O2− and F− are respectively: (1) 1. 71, 1. 36 and 1. 40 (2) 1. 36, 1. 40 and 1. 71 (3) 1. 36, 1. 71 and 1. 40 (4) 1. 71, 1. 40 and 1. 36

Q34.The intermolecular interaction that is dependent on the inverse cube of distance between the molecules is: (1) Hydrogen bond (2) Ion-ion interaction (3) Ion-dipole interaction (4) London force

Q34.The shape of XeOF4 by VSEPR theory is: (1) Trigonal bipyramidal (2) Square pyramidal (3) Pentagonal planar (4) Octahedral

Q35.The following reaction is performed at 298 K. 2NO(g) + O2(g) ⇌2NO2(g) The standard free energy of the formation of NO(g) is 86. 6 kJ mol−1 at 298 K. What is the standard free energy of the formation of NO2(g) at 298 K? (KP = 1.6 × 1012) (1) 0.5[2 × 86,600 −R(298) ln (1.6 × 1012)] (2) R(298) ln(1.6 × 1012)−86,600 (3) 86,600 + R(298) ln (1.6 × 1012) (4) 86,600 − ln(1.6×1012)R(298)