Practice Questions

Q52.The length of a given cylindrical wire is increased by 100%. Due to the consequent decrease in diameter the change in the resistance of the wire will be (1) 200% (2) 100% (3) 50% (4) 300%

Q54.A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through 60∘ . The torque needed to maintain the needle in this position will be (1) √3 W (2) W (3) √3 2 W (4) 2 W JEE Main 2003 JEE Main Previous Year Paper

Q58.A particle of charge −16 × 10−18 coulomb moving with velocity 10 ms−1 along the x-axis enters a region where a magnetic field of induction B is along the y-axis, and an electric field of magnitude 104 V/m is along the negative z-axis. If the charged particle continues moving along the x-axis, the magnitude of B is (1) 103 Wb/m2 (2) 105 Wb/m2 (3) 1016 Wb/m2 (4) 10−3 Wb/m2

Q60.When the current changes from +2 A to −2 A in 0.05 second, an e.m.f. of 8 V is induced in a coil. The coefficient of self-induction of the coil is (1) 0.2H (2) 0.4H (3) 0.8H (4) 0.1H

Q61.In an oscillating LC circuit the maximum charge on the capacitor is Q. The charge on the capacitor when the energy is stored equally between the electric and magnetic field is (1) Q (2) Q 2 √3 (3) Q (4) Q √2

Q63.A metal wire of linear mass density of 9.8 g/m is stretched with a tension of 10 kg-wt between two rigid supports 1 metre apart. The wire passes at its middle point between the poles of a permanent magnet, and it vibrates in resonance when carrying an alternating current of frequency n. The frequency n of the alternating source is JEE Main 2003 JEE Main Previous Year Paper (1) 50 Hz (2) 100 Hz (3) 200 Hz (4) 25 Hz

Q67.Two identical photocathodes receive light of frequencies f1 and f2 . If the velocities of the photo electrons (of mass m ) coming out are respectively v1 and v2 , then (1) v21 −v22 = 2hm (f1 −f2) (2) v1 + v2 = [ 2hm (f1 + f2)] 1/2 (3) v21 + v22 = 2hm (f1 + f2) (4) v1 −v2 = [ 2hm (f1 −f2)] 1/2

Q69.The wavelengths involved in the spectrum of deuterium (21D) are slightly different from that of hydrogen spectrum, because (1) the size of the two nuclei are different (2) the nuclear forces are different in the two cases (3) the masses of the two nuclei are different (4) the attraction between the electron and the nucleus is different in the two cases

Q70.If the binding energy of the electron in a hydrogen atom is 13.6eV, the energy required to remove the electron from the first excited state of Li++ is (1) 30.6eV (2) 13.6eV (3) 3.4eV (4) 122.4eV

Q72.When a U 238 nucleus originally at rest, decays by emitting an alpha particle having a speed ' u ', the recoil speed of the residual nucleus is (1) 238 4u (2) −4u234 (3) 234 4u (4) −4u238 JEE Main 2003 JEE Main Previous Year Paper

Q73.A radioactive sample at any instant has its disintegration rate 5000 disintegrations per minute. After 5 min− utes, the rate is 1250 disintegrations per minute. Then, the decay constant (per minute) is (1) 0.4 ln 2 (2) 0.2 ln 2 (3) 0.1 ln 2 (4) None of these

Q74.A nucleus with Z = 92 emits the following in a sequence: α, β−, β−α, α, α, α, α, β−, β−, α, β+, β+, α. Then Z of the resulting nucleus is (1) 76 (2) 78 (3) 82 (4) 74

Q75.Which of the following cannot be emitted by radioactive substances during their decay? (1) Protons (2) Neutrinoes (3) Helium nuclei (4) Electrons

Q76.The difference in the variation of resistance with temperature in a metal and a semiconductor arises essentially due to the difference in the (1) crystal structure (2) variation of the number of charge carriers with temperature (3) type of bonding (4) variation of scattering mechanism with temperature

Q77.In the middle of the depletion layer of a reverse biased p-n junction, the (1) electric field is zero (2) potential is maximum (3) electric field is maximum (4) potential is zero

Q79.What volume of hydrogen gas, at 273 K and 1 atm, pressure will be consumed in obtaining 21.6 g of elemental boron (atomic mass = 10.8 ) from the reducti on of boron trichloride by hydrogen? (1) 67.2 L (2) 44.8 L (3) 22.4 L (4) 89.6 L Q80. 25ml of a solution of barrium hydroxide on titration with a 0.1 molar solution of hydrochloric acid gave a litre value of 35ml. The molarity of barium hydroxide solution was (1) 0.14 (2) 0.28 (3) 0.35 (4) 0.07

Q81.The orbital angular momentum for an electron revolving in an orbit is given by √l(l + 1) ⋅ 2πh . This momentum for an s-electron will be given by (1) zero (2) h 2π (3) √2 ⋅ 2πh (4) + 21 ⋅ 2πh JEE Main 2003 JEE Main Previous Year Paper

Q84.The de Broglie wavelength of a tennis ball of mass 60 g moving with a velocity of 10 metres per second is approximately (1) 10−31 metres (2) 10−16 metres (3) 10−25 metres (4) 10−33 metres Planck's constant, h = 6.63 × 10−34Js.

Q86.According to the Periodic Law of elements, the variation in properties of elements is related to their (1) nuclear masses (2) atomic numbers (3) nuclear neutron-proton number ratios (4) atomic masses

Q88.Which one of the following pairs of molecules will have permanent dipole moments for both members? (1) NO2 and CO2 (2) NO2 and O3 (3) SiF4 and CO2 (4) SiF4 and NO2

Q89.Which one of the following compounds has the smallest bond angle in its molecule? (1) OH2 (2) SH2 (3) NH3 (4) SO2

Q90.The pair of species having identical shapes for molecules of both species is (1) XeF2, CO2 (2) BF3, PCl3 (3) PF5, IF5 (4) CF4, SF4

Q91.According to the kinetic theory of gases, in an ideal gas, between two successive collisions a gas molecule travels (1) in a wavy path (2) in a straight line path (3) with an accelerated velocity (4) in a circular path JEE Main 2003 JEE Main Previous Year Paper

Q93.If at 298 K the bond energies of C −H, C −C, C = C and H −H bonds are respectively 414, 347, 615 and 435 kJ mol−1 , the value of enthalpy change for the reaction H2C = CH2( g) + H2( g) →H3C −CH3( g) at 298 K will be (1) −250 kJ (2) +125 kJ (3) −125 kJ (4) +250 kJ

Q94.In an irreversible process taking place at constant T and P and in which only pressure-volume work is being done, the change in Gibbs free energy (dG) and change in entropy (dS), satisfy the criteria (1) (dS)V,E > 0, (dG)T,P < 0 (2) (dS)V:E = 0, (dG)TPP = 0 (3) (dS)V,E = 0, (dG)T,P > 0 (4) (dS)V,E < 0, (dG)T,P < 0