Practice Questions

Q18.The half-life of 198Au is 3 days. If atomic weight of 198Au is 198 g mol-1, then the activity of 2 mg of 198Au is [in disintegration second-1]: (1) 2 . 67 × 1012 (2) 6 . 06 × 1018 (3) 32 . 36 × 1012 (4) 16 . 18 × 1012

Q18.A monochromatic neon lamp with wavelength of 670. 5 nm illuminates a photo-sensitive material which has a stopping voltage of 0. 48 V . What will be the stopping voltage if the source light is changed with another source of wavelength of 474. 6 nm ? (1) 0. 24 V (2) 1. 5 V (3) 1. 25 V (4) 0. 96 V

Q18.A ray of light entering from air into a denser medium of refractive index 4 , as shown in figure. 3 The light ray suffers total internal reflection at the adjacent surface as shown. The maximum value of angle θ should be equal to: JEE Main 2021 (25 Jul Shift 2) JEE Main Previous Year Paper (1) sin−1 √73 (2) sin−1 √54 (3) sin−1 √74 (4) sin−1 √53

Q18.The temperature of an ideal gas in three dimensions is 300 K . The corresponding de-Broglie wavelength of the electron approximately at 300 K is: 𝑚𝑒= mass of electron = 9 × 10-31 kg, ℎ= Planck constant = 6 . 6 × 10-34 J s, 𝑘𝐵= Boltzmann constant = 1 . 38 × 10-23 J K-1 (1) 2 . 26 nm (2) 3 . 25 nm (3) 8 . 46 nm (4) 6 . 26 nm

Q19.Consider a situation in which reverse biased current of a particular P −N junction increases when it is exposed to a light of wavelength ≤621 nm. During this process, enhancement in carrier concentration takes place due to generation of hole-electron pairs. The value of band gap is nearly. (1) 2 eV (2) 4 eV (3) 1 eV (4) 0. 5 eV

Q19.A nucleus of mass M emits γ -ray photon of frequency v. The loss of internal energy by the nucleus is: [Take c as the speed of electromagnetic wave] (1) hv (2) 0 (3) hv[1 − 2Mc2hv ] (4) hv[1 + 2Mc2hv ]

Q19.The output of the given combination gates represents: JEE Main 2021 (17 Mar Shift 1) JEE Main Previous Year Paper (1) XOR Gate (2) NAND Gate (3) AND Gate (4) NOR Gate

Q19.There are 1010 radioactive nuclei in a given radioactive element. Its half-life time is 1 min. How many nuclei = 1. will remain after 30 s? (√2 414) (1) 7 × 109 (2) 105 (3) 2 × 1010 (4) 4 × 1010

Q19.In the given figure, the energy levels of hydrogen atom have been shown along with some transitions marked 𝐴, 𝐵, 𝐶, 𝐷 and 𝐸. The transitions 𝐴, 𝐵 and 𝐶 respectively represent (1) The ionization potential of hydrogen, second (2) The series limit of Lyman series, second member member of Balmer series and third member of of Balmer series and second member of Paschen Paschen series. series. (3) The series limit of Lyman series, third member of (4) The first member of the Lyman series, third Balmer series and second member of Paschen member of Balmer series and second member of series. Paschen series.

Q19.Four NOR gates are connected as shown in figure. The truth table for the given figure is : (1) A B Y (2) A B Y 0 0 1 0 0 0 0 1 0 0 1 1 1 0 1 1 0 1 1 1 0 1 1 0 (3) A B Y (4) A B Y 0 0 1 0 0 0 0 1 0 0 1 1 1 0 0 1 0 0 1 1 1 1 1 1

Q19.Given below are two statements: Statement I : A speech signal of 2 kHz is used to modulate a carrier signal of 1 MHz. The bandwidth requirement for the signal is 4 kHz. Statement II : The side band frequencies are 1002 kHz and 998 kHz. In the light of the above statements, choose the correct answer from the options given below: (1) Statement I is false but Statement II is true (2) Both Statement I and Statement II are true (3) Statement I is true but Statement II is false (4) Both Statement I and Statement II are false

Q19.The half life period of a radioactive element 𝑥 is same as the mean life time of another radioactive element 𝑦. Initially they have the same number of atoms. Then: (1) 𝑥 and 𝑦 decay at the same rate always. (2) 𝑥-will decay faster than 𝑦. (3) 𝑦-will decay faster than 𝑥. (4) 𝑥 and 𝑦 have same decay rate initially and later on different decay rate. JEE Main 2021 (01 Sep Shift 2) JEE Main Previous Year Paper

Q19.Consider the following statements: A . Atoms of each element emit characteristics spectrum. B. According to Bohr's Postulate, an electron in a hydrogen atom revolves in a certain stationary orbit. C. The density of nuclear matter depends on the size of the nucleus. D. A free neutron is stable but a free proton decay is possible. E. Radioactivity is an indication of the instability of nuclei. Choose the correct answer from the options given below. (1) A, B, C, D and E (2) A, B and E only. (3) B and D only (4) A, C and E only

Q19.Statement I: By doping silicon semiconductors with pentavalent material, the electrons density increases. Statement II: The n−type of semiconductor has a net negative charge. In the above statements, choose the most appropriate answer from the options given below: (1) Both Statement I and Statement II are false. (2) Statement I is true but Statement II is false. (3) Statement I is false but Statement II is true. (4) Both Statement I and Statement II are true.

Q19.An electron moving with speed v and a photon moving with speed c, have the same D-Broglie wavelength. The ratio of the kinetic energy of the electron to that of a photon is: (1) 3c (2) v v 3c (3) v (4) 2c 2c v

Q19.An electron having de-Broglie wavelength λ is incident on a target in a X -ray tube. Cut-off wavelength of emitted X -ray is: (1) 0 (2) 2 m2c2λ2 h2 (3) 2mcλ2 (4) hc h mc

Q19.A radioactive sample is undergoing α decay, At any time t1, its activity is A and another time t2, the activity is A . What is the average life time for the sample ? 5 (1) ln 5 (2) ln(t2+t1) t2−t1 2 (3) t2−t1 (4) t1−t2 ln 5 ln 5

Q19.The decay of a proton to neutron is : (1) not possible as proton mass is less than the (2) possible only inside the nucleus neutron mass (3) not possible but neutron to proton conversion is (4) always possible as it is associated only with β+ possible decay

Q19.A radioactive sample disintegrates via two independent decay processes having half lives T (1) and T (2) 1/2 1/2 respectively. The effective half- life T1/2 of the nuclei is : (1) (2) T 1/2+T 1/2 (1) T (2) (2) T1/2 = T 1/2(1) + 1/2 T1/2 = (1) (2) T 1/2−T 1/2 (3) T 1/2T(1) 1/2(2) (4) None of the above T1/2 = (1) (2) T 1/2+T 1/2

Q19.Choose the correct waveform that can represent the voltage across R of the following circuit, assuming the diode is ideal one: JEE Main 2021 (31 Aug Shift 1) JEE Main Previous Year Paper (1) (2) (3) (4)

Q19.For extrinsic semiconductors; when doping level is increased; (1) Fermi-level of p and n- type semiconductors will not be affected. (2) Fermi-level of p-type semiconductor will go upward and Fermi-level of n-type semiconductors will go downward. (3) Fermi-level of both p-type and n-type semiconductors will go upward for T > TF K and downward for T < TF K, where TF is Fermi temperature. (4) Fermi-level of p- type semiconductors will go downward and Fermi-level of n- type semiconductor will go upward.

Q19.If f denotes the ratio of the number of nuclei decayed (Nd) to the number of nuclei at t = 0, (N0) then for a collection of radioactive nuclei, the rate of change of f with respect to time is given as: [λ is the radioactive decay constant] (1) −λ(1 −e−λt) (2) λ(1 −e−λt) (3) λe−λt (4) −λe−λt

Q19.If λ1 and λ2 are the wavelengths of the third member of Lyman and first member of the Paschen series respectively, then the value of λ1 : λ2 is : (1) 7 : 135 (2) 1 : 9 (3) 1 : 3 (4) 7 : 108

Q20.The vernier scale used for measurement has a positive zero error of 0. 2 mm. If while taking a measurement it was noted that 0 on the vernier scale lies between 8. 5 cm and 8. 6 cm. Vernier coincidence is 6, then the correct value of measurement is cm. (least count = 0. 01 cm ) (1) 8. 36 cm (2) 8. 54 cm (3) 8. 58 cm (4) 8. 56 cm

Q20.For the circuit shown below, calculate the value of Iz : JEE Main 2021 (20 Jul Shift 1) JEE Main Previous Year Paper (1) 25 mA (2) 0. 15 A (3) 0. 1 A (4) 0. 05 A