Practice Questions

Q28.A sample originally contained 1020 radioactive atoms, which emit α-particles. The ratio of α particles emitted in the third year to that emitted during the second year is 0.3. How many α particles were emitted in the first year? JEE Main 2012 (07 May Online) JEE Main Previous Year Paper (1) 3 × 1018 (2) 3 × 1019 (3) 5 × 1018 (4) 7 × 1019

Q28.Truth table for system of four NAND gates as shown in figure is (1) (2) (3) (4)

Q28.Which one of the following is the Boolean expression for NOR gate? –– (1) Y = A + B (2) Y = A ⋅B (3) Y = A ⋅B (4) Y = ¯A

Q28.Which of the plots shown in the figure represents speed (v) of the electron in a hydrogen atom as a function of the principal quantum number (n) ? (1) B (2) D (3) C (4) A

Q29.Given the electric field of a complete amplitude modulated wave as Em →E = ^iEc + cos cos ωct (1 Ec ωmt) Where the subscript c stands for the carrier wave and m for the modulating signal. The frequencies present in the modulated wave are (1) ωc and √ω2c + ω2m (2) ωc, ωc + ωm and ωc −ωm (3) ωc and ωm (4) ωc and √ωcωm

Q29.A radar has a power of 1 Kw and is operating at a frequency of 10 GHz. It is located on a mountain top of height 500 m. The maximum distance upto which it can detect object located on the surface of the earth (Radius of earth = 6.4 × 106 m ) is (1) 80 km (2) 16 km (3) 40 km (4) 64 km

Q29.Which logic gate with inputs A and B performs the same operation as that performed by the following circuit? (1) NAND gate (2) OR gate (3) NOR gate (4) AND gate

Q29.The counting rate observed from a radioactive source at t = 0 was 1600 counts s−1 , and t = 8 s, it was 100 counts s−1 . The counting rate observed as counts s−1 at t = 6 s will be (1) 250 (2) 400 (3) 300 (4) 200

Q29.This question has Statement 1 and Statement 2. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement 1: A pure semiconductor has negative temperature coefficient of resistance. Statement 2: On raising the temperature, more charge carriers are released into the conduction band. (1) Statement 1 is false, Statement 2 is true. (2) Statement 1 is true, Statement 2 is false. (3) Statement 1 is true, Statement 2 is true, (4) Statement 1 is true, Statement 2 is true, Statement 2 is not a correct explanation of Statement 2 is the correct explanation of Statement 1. Statement 1.

Q30.A 10 kW transmitter emits radio waves of wavelength 500 m. The number of photons emitted per second by the transmitter is of the order of (1) 1037 (2) 1031 (3) 1025 (4) 1043 JEE Main 2012 (12 May Online) JEE Main Previous Year Paper

Q30.Broadcasting antennas are generally (1) vertical type (2) both vertical and horizontal type (3) omni directional type (4) horizontal type

Q30.A spectrometer gives the following reading when used to measure the angle of a prism. Main scale reading: 58.5 degree Vernier scale reading : 09 divisions Given that 1 division on main scale corresponds to 0.5 degree. Total divisions on the vernier scale is 30 and match with 29 divisions of the main scale. The angle of the prism from the above data (1) 58.59∘ (2) 58.77∘ (3) 58.65∘ (4) 59∘

Q30. N divisions on the main scale of a vernier calliper coincide with (N + 1) divisions of the vernier scale. If each division of main scale is ' a ' units, then the least count of the instrument is (1) a (2) Na (3) N+1 N × a (4) N+1a

Q30.The figure shows a combination of two NOT gates and a NOR gate. JEE Main 2012 (26 May Online) JEE Main Previous Year Paper The combination is equivalent to a (1) NAND gate (2) NOR gate (3) AND gate (4) OR gate

Q31.The concentrated sulphuric acid that is peddled commercial is 95%H2SO4 by weight. If the density of this commercial acid is 1.834 g cm−3 , the molarity of this solution is (1) 17.8M (2) 12.0M (3) 10.5M (4) 15.7M

Q31.An aqueous solution of oxalic acid dihydrate contains its 6.3 g in 250ml. The volume of 0.1 N NaOH required to completely neutralize 10ml of this solution (1) 4ml (2) 20ml (3) 2ml (4) 40ml Q32. 5 g of benzene on nitration gave 6.6 g of nitrobenzene. The theoretical yield of the nitrobenzene will be (1) 4.5 g (2) 5.6 g (3) 8.09 g (4) 6.6 g

Q31.When CO2( g) is passed over red hot coke it partially gets reduced to CO(g). Upon passing 0.5 L of CO2(g) over red hot coke, the total volume of the gases increased to 700 mL. The composition of the gaseous mixture at STP is (1) CO2 = 300 mL; CO = 400 mL (2) CO2 = 0.0 mL; CO = 700 mL (3) CO2 = 200 mL; CO = 500 mL (4) CO2 = 350 mL; CO = 350 mL

Q31.A transition metal M forms a volatile chloride which has a vapour density of 94.8 . If it contains 74.75% of chlorine the formula of the metal chloride will be (1) MCl3 (2) MCl2 (3) MCl4 (4) MCl5

Q31.The density of a solution prepared by dissolving 120 g of urea (mol. Mass = 60u ) in 1000 g of water is 1.15 g/mL. The molarity of this solution is : (1) 0.50 M (2) 1.78 M (3) 1.02 M (4) 2.05 M JEE Main 2012 (Offline) JEE Main Previous Year Paper

Q32.The electrons identified by quantum numbers n and I : (a) n = 4, I = 1 (b) n = 4, l = 0 (c) n = 3, I = 2 (d) n = 3, I = 1 Can be placed in order of increasing energy as: (1) (c) < (d) < (b) < (a) (2) (d) < (b) < (c) < (a) (3) (b) < (d) < (a) < (c) (4) (a) < (c) < (b) < (d)

Q32.The ratio of number of oxygen atoms (O) in 16.0 g ozone (O3), 28.0 g carbon monoxide (CO) and 16.0 oxygen (O2) is (Atomic mass : C = 12, O = 16 and Avogadro's constant NA = 6.0 × 1023 mol−1 ) (1) 3 : 1 : 2 (2) 1 : 1 : 2 (3) 3 : 1 : 1 (4) 1 : 1 : 1

Q32.The following sets of quantum numbers represent four electrons in an atom. (i) n = 4, l = 1 (ii) n = 4, l = 0 (iii) n = 3, l = 2 (iv) n = 3, l = 1 The sequence representing increasing order of energy, is (1) (iii) < (i) < (iv) < (ii) (2) (iv) < (ii) < (iii) < (i) (3) (i) < (iii) < (ii) < (iv) (4) (ii) < (iv) < (i) < (iii)

Q32.Which of the following paramagnetic ions would exhibit a magnetic moment (spin only) of the order of 5BM ? (At. Nos. Mn = 25, Cr = 24, V = 23, Ti = 22 ) (1) Mn2+ (2) Ti2+ (3) V2+ (4) Cr2+

Q33.The limiting line in Balmer series will have a frequency of (Rydberg constant, R∞= 3.29 × 1015 cycles /s ) (1) 8.22 × 1014 s−1 (2) 3.29 × 1015 s−1 (3) 3.65 × 1014 s−1 (4) 5.26 × 1013 s−1

Q33.If the radius of first orbit of H atom is a0 , the deBroglie wavelength of an electron in the third orbit is (1) 4πa0 (2) 8πa0 (3) 6πa0 (4) 2πa0