Dual Nature, Atoms & Nuclei · JEE Main previous year questions

2012 7 questions

1. Q562012 · 26 May 2012 · Shift 1
   
   1. A.$B$
   2. B.$D$
   3. C.$C$
   4. D.$A$
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   Answer: A

2. Q602012 · 26 May 2012 · Shift 1

   The counting rate observed from a radioactive source at $t=0$ was $1600\mathrm{counts}{\mathrm{s}}^{-1}$, and $t=8\mathrm{s}$, it was $100\mathrm{counts}{\mathrm{s}}^{-1}$. The counting rate observed as $\mathrm{counts}{\mathrm{s}}^{-1}$ at $t=6\mathrm{s}$ will be

   1. A.250
   2. B.400
   3. C.300
   4. D.200
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   Answer: D

3. Q542012 · 12 May 2012 · Shift 1

   A hypothetical atom has only three energy levels. The ground level has energy, $E_1=-8\mathrm{eV}$. The two excited states have energies, $E_2=-6\mathrm{eV}$ and $E_3=-2\mathrm{eV}$. Then which of the following wavelengths will not be present in the emission spectrum of this atom?

   1. A.$207\mathrm{nm}$
   2. B.$465\mathrm{nm}$
   3. C.$310\mathrm{nm}$
   4. D.$620\mathrm{nm}$
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   Answer: B

4. Q552012 · 12 May 2012 · Shift 1

   A doubly ionised $Li$ atom is excited from its ground state $(n=1)$ to $n=3$ state. The wavelengths of the spectral lines are given by ${\lambda }_{32},{\lambda }_{31}$ and ${\lambda }_{21}$. The ratio ${\lambda }_{32}/{\lambda }_{31}$ and ${\lambda }_{21}/{\lambda }_{31}$ are, respectively

   1. A.$8.1,0.67$
   2. B.$8.1,1.2$
   3. C.$6.4,1.2$
   4. D.$6.4,0.67$
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   Answer: C

5. Q562012 · 7 May 2012 · Shift 1

   The electron of a hydrogen atom makes a transition from the $(n+1{)}^{\mathrm{th}}$ orbit to the $n^{\mathrm{th}}$ orbit. For large $n$ the wavelength of the emitted radiation is proportional to

   1. A.$n$
   2. B.$n^3$
   3. C.$n^4$
   4. D.$n^2$
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   Answer: B

6. Q572012 · 7 May 2012 · Shift 1
   
   1. A.$D$
   2. B.$B$
   3. C.$C$
   4. D.$A$
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   Answer: C

7. Q592012 · 7 May 2012 · Shift 1

   A sample originally contained $10^{20}$ radioactive atoms, which emit $\alpha$-particles. The ratio of $\alpha$ particles emitted in the third year to that emitted during the second year is 0.3. How many $\alpha$ particles were emitted in the first year?

   1. A.$3\times 10^{18}$
   2. B.$3\times 10^{19}$
   3. C.$5\times 10^{18}$
   4. D.$7\times 10^{19}$
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   Answer: D