Practice Questions

Q18.When photon of energy 4.0eV strikes the surface of a metal A, the ejected photoelectrons have maximum kinetic energy TAeV and de-Broglie wavelength λA. The maximum kinetic energy of photoelectrons liberated from another metal B by photon of energy 4.50eV is TB = (TA −1.5)eV. If the de-Broglie wavelength of these photoelectrons λB = 2λA, then the work function of metal B is: (1) 4eV (2) 2eV (3) 1.5eV (4) 3eV

Q18.A double convex lens has power P and same radii of curvature r of both the surfaces. The radius of curvature of a surface of a plano-convex lens made of the same material with power 1. 5 P is : JEE Main 2020 (06 Sep Shift 2) JEE Main Previous Year Paper (1) 2R (2) R2 (3) 3R (4) R 2 3 ¯

Q18.A particle is moving 5 times as fast as an electron. The ratio of the de-Broglie wavelength of the particle to that of the electron is 1. 878 × 10–4 . The mass of the particle is close to : (1) 4. 8 × 10−27 kg (2) 9. 1 × 10−31 kg (3) 1. 2 × 10−28 kg (4) 9. 7 × 10−28 kg

Q18.In a double – slit experiment, at a certain point on the screen the path difference between the two interfering waves is 1 8 th of a wavelength. The ratio of the intensity of light at that point to that at the center of a bright fringe is: (1) 0.853 (2) 0.672 (3) 0.568 (4) 0.760 →

Q18.You are given that 73Li = 7. 0160u,Mass of Mass of 42He = 4. 0026u and Mass of 11He = 1. 0079H When 20g of 73Li is converted into 42 He by proton capture, the energy liberated, (in kWh ), is : [Mass of nucleon = 1 GeV /c2 ] (1) 4. 5 × 105 (2) 8 × 106 (3) 6. 82 × 105 (4) 1. 33 × 106

Q18.An electron of mass m and magnitude of charge e at rest, gets accelerated by a constant electric field E . The rate of change of de-Broglie wavelength of this electron at a time t is (ignore relativistic effects) (1) dλ dt = − eEth (2) dλdt = −2heEt (3) dλ dt = −2heEt2 (4) dλdt = − eEt2h

Q19.An electron (of mass m ) and a photon have the same energy E in the range of a few eV . The ratio of the de- Broglie wavelength associated with the electron and the wavelength of the photon is ( c = speed of light in vacuum) (1) 1 c ( 2Em ) 1/2 (2) c(2mE)1/2 (3) 1 E 1/2 (4) E 1/2 c ( 2m ) ( 2m )

Q19.Find the Binding energy per nucleon for 12050Sn. Mass of proton mp = 1. 00783 U , mass of neutron mn = 1. 00867 U and mass of tin nucleus msn = 119. 902199 U . (take 1U = 931 MeV ) (1) 7 .5 MeV (2) 9. 0MeV (3) 8.0MeV (4) 8 .5 MeV

Q19.The radius R of a nucleus of mass number A can be estimated by the formula R = (1. 3 × 10−15)A1/3m . It follows that the mass density of n nucleus is of the order of: (Mprot ≅Mneut ≃1. 67 × 10−27 kg) (1) 103 kg m−3 (2) 1010 kg m−3 (3) 1024 kg m−3 (4) 1017 kg m−3

Q19.When a diode is forward biased, it has a voltage drop of 0. 5 V . the safe limit of current through the diode is 10 mA . If a battery of emf 1. 5 V is used in the circuit, the value of minimum resistance to be connected in series with the diode so that the current does not exceed the safe limit is : (1) 300 Ω (2) 50 Ω (3) 100 Ω (4) 200 Ω

Q19.A radioactive nucleus decays by two different processes. The half-life for the first process is 10 s and that for the second is 100 s. The effective half-life of the nucleus is close to: (1) 9 s (2) 6 s (3) 55 s (4) 12 s

Q19.An amplitude modulated waves is represented by expression vm = 5(1 + 0. 6 cos 6280t) sin(211 × 104t) V. The minimum and maximum amplitudes of the amplitudes modulated wave are, respectively: (1) 2 3 V, 5V (2) 52 V, 8V (3) 5V, 8V (4) 3V, 5V

Q19.A particle moving with kinetic energy E has de Broglie wavelength λ . If energy ΔE is added to its energy, the wavelength become λ . Value of ΔE, is: 2 (1) E (2) 4E (3) 3E (4) 2E

Q19.Identify the correct output signal Y in the given combination of gates (as shown n) for the given inputs A and B JEE Main 2020 (06 Sep Shift 1) JEE Main Previous Year Paper (1) (2) (3) (4)

Q19.The energy required to ionise a hydrogen like ion in its ground state is 9 Rydbergs. What is the wavelength of the radiation emitted when the electron in this ion jumps from the second excited stale to the ground state? (1) 24. 2nm (2) 11.4nm (3) 35.8nm (4) 8.6nm

Q19.Activities of three radioactive substances A, B and C are represented by the curves A, B and C, in the figure. Then their half-lives T 1 (A) : T 1 (B) : T 1 (C) are in the ratio: 2 2 2 JEE Main 2020 (05 Sep Shift 1) JEE Main Previous Year Paper (1) 2 : 1 : 1 (2) 3 : 2 : 1 (3) 2 : 1 : 3 (4) 4 : 3 : 1

Q19.The time period of revolution of electron in its ground state orbit in a hydrogen atom is 1.6 × 10−16s. The frequency of revolution of the electron in its first excited state (in s−1 ) is: (1) 1.6 × 1014 (2) 7.8 × 1014 (3) 6.2 × 1015 (4) 5.6 × 1012

Q19.Given figure shows few data points in a photo-electric effect experiment for a certain metal. The minimum energy for ejection of electrons from its surface is: (Planck's constant h = 6.62 × 10–34 J.s) (1) 2.27 eV (2) 2.59 eV (3) 1.93 eV (4) 2.10 eV

Q19.In a hydrogen atom the electron makes a transition from (n + 1)th level to the nth level. If n >> 1 , the frequency of radiation emitted is proportional to : (1) 1 (2) 1 n n3 (3) 1 (4) 1 n2 n4

Q19.The graph which depicts the results of Rutherford gold foil experiment with α -particles is: θ : Scattering angle Y : Number of scattered α -particles detected (Plots are schematic and not to scale) JEE Main 2020 (08 Jan Shift 1) JEE Main Previous Year Paper (1) (2) (3) (4)

Q19.An electron (mass m ) with initial velocity →v= v0ˆi + v0ˆj is in an electric filed E = −E0ˆk. If λ0 is initial de- Broglie wavelength of electron, its de-Broglie wave length at time t is given by: (1) λ0√2 (2) λ0 m2v2 0 √1+ e2E2t2m2v20 √1+ e2E2t2 (3) λ0 (4) λ0 m2v2 √1+ e2E2t22m2v20 √2+ e2E2t2 0

Q19.Given the masses of various atomic particles mP = 1, 0072 u , mn = 1, 0087 u , me = 0 .000548 u , mv = 0 , ¯¯md = 2 .0141 u , where p =proton, n ≡neutron, e ≡electron, v ≡antineutrino and d ≡deuteron. Which of the following process is allowed by momentum and energy conservation : ¯(1) n + n → deuterium atom (electron bound to the (2) p →n + e+ + v nucleus) (3) n + p →d + γ (4) e+ + e−→γ

Q20.The activity of a radioactive sample falls from 700s−1 to 500s−1 in 30 minutes. Its half life is close to: (1) 72min (2) 62min (3) 66min (4) 52min → → → → → → → →

Q20.If a semiconductor photo diode can detect a photon with a maximum wavelength of 400 nm, then its band gap energy is: Planck's constant h = 6. 63 × 10−34 J. s Speed of light c = 3 × 108 m s−1 (1) 1. 1 eV (2) 2. 0 eV (3) 1. 5 eV (4) 3. 1 eV

Q20.The current i in the network is (1) 0.2 A (2) 0.6 A (3) 0.3 A (4) 0 A