Atoms And Nuclei(12th Grade > Physics ) Questions and answers for exam Preparation

12th Grade > Physics

ATOMS AND NUCLEI MCQs

Atoms, Nuclei (12th Grade)

Total Questions : 60 | Page 4 of 6 pages

Question 31. Unit of radioactivity is rutherford. Its value is

3.7×1010 disintegrations/sec
3.7×106 disintegrations/sec
1.0×1010 disintegrations/sec
1.0×106 disintegrations/sec

Discuss Question

Answer: Option D. -> 1.0×106 disintegrations/sec
:
D

1.0 \times 10^{6}

disintegrations/sec

Question 32. When

_{92} U^{235}

undergoes fission. 0.1% of its original mass is changed into energy. How much energy is released if 1 kg of

_{92} U^{235}

undergoes fission

9×1010J
9×1011J
9×1012J
9×1013J

Discuss Question

Answer: Option D. -> 9×1013J
:
D
By using

E = Δ m . c^{2} \Rightarrow E = (\frac{0.1}{100} \times 1) (3 \times 10^{8})^{2} = 9 \times 10^{13} J

Question 33. Which of the following statement is correct

The rest mass of a stable nucleus is equal to the sum of the rest masses of its separated nucleons
The rest mass of a stable nucleus is greater than the sum of the rest masses of its separated nucleons.
In nuclear fusion, energy is released by fusing two nuclei of medium mass (approximately 100 a.m.u.)
In nuclear fission, energy is released by fragmentation of a very heavy nucleus

Discuss Question

Answer: Option D. -> In nuclear fission, energy is released by fragmentation of a very heavy nucleus
:
D
In nuclear fission, energy is released by fragmentation of a very heavy nucleus

Question 34. The transition from the state n = 4 to n = 3 in a hydrogen like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition from :

3→2
4→2
5→4
2→1

Discuss Question

Answer: Option C. -> 5→4
:
C
Infra- red radiation has lesser energy than Ulta-Violet radiation. Hence the transition should take place between energy levels which have lesser energy.

5 \to 4

Question 35. The ground state energy of hydrogen atom is -13.6eV. The kinetic energy of the electron in this state is:

1.85 eV
13.6 eV
6.8 eV
3.4 eV

Discuss Question

Answer: Option B. -> 13.6 eV
:
B
KE=-E
K.E. = 13.6 eV

Question 36. Energy required for the electron excitation in

L i^{+ +}

from the first to the third Bohr orbit is :

36.3 eV
108.8 eV
122.4 eV
12.1 eV

Discuss Question

Answer: Option B. -> 108.8 eV
:
B

E = - 13.6 \frac{z^{2}}{n^{2}}

E_{1} = - 13.6 \times \frac{3^{2}}{1} = - 13.6 \times 9

E_{3} = - 13.6 \times \frac{3^{2}}{3^{2}} = - 13.6

E_{3} - E_{1} = - 13.6 + (13.6 \times 9)

= 108.8 e V

Question 37. If 13.6 ev energy is required to ionise the hydrogen atom, then the energy required to remove an electron from first exited state (n = 2) is

10.2 eV
0 eV
3.4 eV
6.8 eV

Discuss Question

Answer: Option C. -> 3.4 eV
:
C

E_{2} = - \frac{13.6}{n^{2}} = - \frac{13.6}{2^{2}}

= - 3.4 e V

E = 3.4 e V

Question 38. The energy of the ground electronic state of hydrogen atom is -13.6 eV. The energy of the first excited stae will be :

– 52.4 eV
– 27.2 eV
– 68 eV
– 3.4 eV

Discuss Question

Answer: Option D. -> – 3.4 eV
:
D

E = - \frac{13.6}{n^{2}} n = 2

= - \frac{13.6}{n^{2}} = - 3.4 e V

Question 39. In Bohr’s model of hydrogen atom, the ratio between the period of revolution of an electron in orbit n = 1 to the period of the electron in the orbit n = 2 is

1 : 2
2 : 1
1 : 4
1 : 8

Discuss Question

Answer: Option D. -> 1 : 8
:
D