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Set 7 of 14 · Questions 181-210 of 394

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Mere Teacher · Previous Year Questions NEET Physics · Atoms · Set 7 (Q181-210)
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181. $Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes, respectively, Initially, the samples have equal number of nuclei. After 80 minutes, the ratio of decayed numbers of A and B nuclei will be :$ (1) $4 : 1$ (2) $1 : 4$ (3) $5 : 4$ (4) $1 : 16$ 182. $An excited H e^{+} ion emits two photons in succession, with wavelengths 108.5 nm and 30.4 nm, in making a transition to ground state. The quantum number n, corresponding to its initial excited state is (for photon of wavelength λ, energy E = \frac{1240 eV}{λ ( innm )})$ (1) $n = 4$ (2) $n = 5$ (3) $n = 7$ (4) $n = 6$ 183. $Out of the following which one is not a possible energy for a photon to be emitted by hydrogen atom according to Bohr’s atomic model?$ (1) $1.9 eV$ (2) $11.1 eV$ (3) $13.6 eV$ (4) $0.65 eV$ 184. $If ' μ' is the magnetic moment of an electron revolving around hydrogen nucleus in an orbit of principal quantum number ' n', then$ (1) $μ \propto n^{2}$ (2) $μ \propto n$ (3) $μ \propto \frac{1}{n}$ (4) $μ \propto \frac{1}{n ^{2}}$ 185. $A sample of radioactive material A, that has an activity of 10 mCi (1 Ci = 3.7 \times 1 0^{10} decays/s), has twice the number of nuclei as another sample of a different radioactive material B which has an activity of 20 mCi. The correct choices for half-lives of A and B would then be respectively:$ (1) $10 days and 40 days$ (2) $20 days and 5 days$ (3) $5 days and 10 days$ (4) $20 days and 10 days$ 186. $In photoelectric emission process from a metal of work function 1.8 eV, the kinetic energy of most energetic electrons is 0.5 eV. The corresponding stopping potential is:$ (1) $1.8 V$ (2) $1.2 V$ (3) $0.5 V$ (4) $2.3 V$ 187. $Statement-I: A nucleus having energy E_{1} decays by β^{-} emission to daughter nucleus having energy E_{2}, but the β^{-} rays are emitted with a continuous energy spectrum having end point energy E_{1} - E_{2} . Statement-II: To conserve energy and momentum in β^{-} decay at least three particles must take part in the transformation.$ (1) $Statement-I is correct but statement-II is not correct.$ (2) $Statement-I and statement-II both are correct and statement-II is the correct explanation of statement-I.$ (3) $Statement-I is correct, statement-II is correct and statement-II is not the correct explanation of statement-I$ (4) $Statement-I is incorrect, statement-II is correct.$ 188. $If radius of the_{13}^{27} Al nucleus is taken to be R_{AI}, then the radius of_{53}^{125} Te nucleus is nearly$ (1) $(\frac{53}{13})^{\frac{1}{3}} R_{Al}$ (2) $\frac{5}{3} R_{Al}$ (3) $\frac{3}{5} R_{Al}$ (4) $(\frac{13}{53})^{\frac{1}{3}} R_{Al}$ 189. $An electron in an excited state of Li^{2 +} ion has angular momentum \frac{3 h}{2 π} . The de Broglie wavelength of electron in this state is Pπ a_{n} (where a_{0} = Bohr radius). The value of P is$ (1) $3$ (2) $2$ (3) $1$ (4) $4$ 190. $The mass number of nucleus having radius equal to half of the radius of nucleus with mass number 192 is:$ (1) $24$ (2) $32$ (3) $40$ (4) $20$ 191. $An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius r . The Coulomb force F between the two is (where K = \frac{1}{4 π ϵ _{0}})$ (1) $K \frac{e ^{2}}{r ^{2}} r$ (2) $- K \frac{e ^{2}}{r ^{2}} r$ (3) $K \frac{e ^{2}}{r ^{3}} r$ (4) $- K \frac{e ^{2}}{r ^{3}} r$ 192. $The total energy of an electron revolving in the second orbit of hydrogen atom is$ (1) $- 13.6 eV$ (2) $- 1.51 eV$ (3) $- 3.4 eV$ (4) $zero$ 193. $If an electron in a hydrogen atom jumps from the 3^{rd} orbit to the 2^{nd} orbit, it emits a photon of wavelength λ . When it jumps from the 4^{th} orbit to the 3^{rd} orbit, the corresponding wavelength of the photon will be$ (1) $\frac{16}{25} λ$ (2) $\frac{9}{16} λ$ (3) $\frac{20}{7} λ$ (4) $\frac{20}{13} λ$ 194. $Hydrogen ion and singly ionized helium atom are accelerated, from rest, through the same potential difference. The ratio of final speeds of hydrogen and helium ions is close to$ (1) $02:01$ (2) $01:02$ (3) $10:07$ (4) $05:07$ 195. $In Bohr's theory of Hydrogen atom, the electron jumps from higher orbit n to lower orbit p . The wavelength will be minimum for the transition$ (1) $n = 5 to p = 4$ (2) $n = 4 to p = 3$ (3) $n = 3 to p = 2$ (4) $n = 2 to p = 1$ 196. $If an electron in hydrogen atom jumps from an orbit of level n = 3 to an orbit of level n = 2, the emitted radiation has a frequency (R = Rydberg constant, C = velocity of light)$ (1) $\frac{RC}{25}$ (2) $\frac{5 RC}{36}$ (3) $\frac{3 RC}{27}$ (4) $\frac{8 RC}{9}$ 197. $The potential difference that must be applied to stop the fastest photoelectrons emitted by a nickel surface, having work function 5.01 eV, when ultraviolet light of 200 nm falls on it, must be$ (1) $2.4 V$ (2) $-1.2 V$ (3) $- 2.4 V$ (4) $1.2 V$ 198. $An electron is moving in an orbit of a hydrogen atom from which there can be a maximum of six transitions. An electron is moving in an orbit of another hydrogen atom from which there can be a maximum of three transitions. The ratio of the velocity of the electron in these two orbits is$ (1) $½$ (2) $2/1$ (3) $5/4$ (4) $3/4$ 199. $If the series limit frequency of the Lyman series is v_{L}, then the series limit frequency of the Pfund series is :$ (1) $v_{L} /16$ (2) $v_{L} /25$ (3) $25 v_{L}$ (4) $16 v_{L}$ 200. $The half life of a radioactive substance is 20 minutes. The approximate time interval (t_{2} - t_{1}) between the time t_{2} when \frac{2}{3} of it has decayed and time t_{1} when \frac{1}{3} of it had decayed is:$ (1) $7 min$ (2) $14 min$ (3) $20 min$ (4) $28 min$ 201. $When a metallic surface is illuminated with radiation of wavelength λ the stopping potential is V. If the same surface is illuminated with radiation of wavelength 2 λ, the stopping potential is \frac{V}{4} . The threshold wavelength for the metallic surface is:$ (1) $3 λ$ (2) $4 λ$ (3) $5 λ$ (4) $\frac{5}{2} λ$ 202. $The centripetal acceleration ' a' of an electron in an orbit of hydrogen and the principal quantum number ' n' of the orbit are related by$ (1) $a \propto n^{2}$ (2) $a \propto \frac{1}{n ^{2}}$ (3) $a \propto n^{4}$ (4) $\propto \frac{1}{n ^{4}}$ 203. $Considering the Bohr model of hydrogen like atoms, the ratio of the radius of 5^{th} orbit of the electron in Li^{2 +} and He^{+} is$ (1) $\frac{3}{2}$ (2) $\frac{2}{3}$ (3) $\frac{4}{9}$ (4) $\frac{9}{4}$ 204. $Ratio of longest wavelength corresponding to Lyman and Balmer series in Hydrogen spectrum is$ (1) $\frac{7}{29}$ (2) $\frac{9}{31}$ (3) $\frac{5}{27}$ (4) $\frac{3}{23}$ 205. $A hydrogen atom in ground state is given an energy of 10.2 eV . How many spectral lines will be emitted due to transition of electrons?$ (1) $6$ (2) $3$ (3) $10$ (4) $1$ 206. $Taking the wavelength of first Balmer line in hydrogen spectrum (n = 3 to n = 2) as 660 nm, the wavelength of the 2ndBalmer line (n = 4 to n = 2) will be;$ (1) $889.2 nm$ (2) $488.9 nm$ (3) $642.7 nm$ (4) $388.9 nm$ 207. $Which of the following spectral series of hydrogen atom is lying in visible range of electromagnetic wave?$ (1) $Lyman series$ (2) $Paschen series$ (3) $Balmer series$ (4) $Pfund series$ 208. $The atomic hydrogen emits a line spectrum consisting of various series. Which series of hydrogen atomic spectra is lying in the visible region?$ (1) $Brackett series$ (2) $Paschen series$ (3) $Lyman series$ (4) $Balmer series$ 209. $The ionization energy of Li^{++} is equal to$ (1) $9 hcR$ (2) $6 hcR$ (3) $2 hcR$ (4) $hcR .$ 210. $The ratio of wavelengths of the last line of Balmer series and the last line of Lyman series is$ (1) $1$ (2) $4$ (3) $0.5$ (4) $2$