Practice Questions

Q25.Hydrogen atom is excited from ground state to another state with principal quantum number equal to 4. Then the number of spectral lines in the emission spectra will be (1) 2 (2) 3 (3) 5 (4) 6

Q27.Assume that a neutron breaks into a proton and an electron. The energy released during this process is (Mass of neutron = 1.6725 × 10−27 kg; mass of proton = 1.6725 × 10−27 kg; mass of electron = 9 × 10−31 kg) (1) 0.73 MeV (2) 7.10 MeV (3) 6.30 MeV (4) 5.4 MeV

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

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.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

Q15.If the terminal speed of a sphere of gold (density = 19.5 kg/m3 ) is 0.2 m/s in a viscous liquid (density = 1.5 kg/m3 ) of the same size in the same liquid. (1) 0.2 m/s (2) 0.4 m/s (3) 0.133 m/s (4) 0.1 m/s

Q51.If the binding energy per nucleon in 73Li and 42He nuclei are 5.60MeV and 7.06MeV respectively, then in the reaction p + 73Li →242He energy of proton must be (1) 39.2MeV (2) 28.24MeV (3) 17.28MeV (4) 1.46MeV

Q52.If the ratio of the concentration of electrons that of holes in a semiconductor is 7 and the ratio of currents is 7 , 5 4 then what is the ratio of their drift velocities? (1) 4 (2) 5 7 8 (3) 4 (4) 5 5 4

Q53.In a common base mode of a transistor, t collector current is 5.488 mA for an emit current of 5.60 mA. The value of the base current amplification factor (β) will be (1) 48 (2) 49 (3) 50 (4) 51

Q56.The circuit has two oppositely connect ideal diodes in parallel. What is the current following in the circuit? (1) 1.33 A (2) 1.71 A (3) 2.00 A (4) 2.31 A

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

Q65.To get three images of a single object, one should have two plane mirrors at an angle of (1) 60∘ (2) 90∘ (3) 120∘ (4) 30∘

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

Q24.A cylinder of height 20 m is completely filled with water. The velocity of efflux of water (in ms−1 ) through a small hole on the side wall of the cylinder near its bottom is (1) 10 (2) 20 (3) 25.5 (4) 5

Q57. The inductance between A and D is (1) 3.66 H (2) 9 H (3) 0.66 H (4) 1 H JEE Main 2002 JEE Main Previous Year Paper