#### 12th Standard Physics Atomic and Nuclear physics English Medium Free Online Test One Mark questions 2020 - 2021

12th Standard

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Physics

Time : 00:20:00 Hrs
Total Marks : 20
20 x 1 = 20
1. Suppose an alpha particle accelerated by a potential of V volt is allowed to collide with a nucleus whose atomic number is Z, then the distance of closest approach of alpha particle to the nucleus is

(a)

$14.4\frac { Z }{ V } \mathring { A }$

(b)

$14.4\frac { V }{ Z } \mathring { A }$

(c)

$1.44\frac { Z }{ V } \mathring { A }$

(d)

$1.44\frac { V }{ Z } \mathring { A }$

2. The ratio of the wavelengths for the transition from n=2 to n=1 in Li++, He+ and H is

(a)

1:2:3

(b)

1:4:9

(c)

3:2:1

(d)

4:9:36

3. the nuclear radius of 27 al is 3.6 fermi, the approximate nuclear radius of 64Cu is

(a)

24

(b)

1.2

(c)

4.8

(d)

3.6

4. A radioactive nucleus (initial mass number A and atomic number Z) emits 2α and 2 positrons. The ratio of number of neutrons to that of proton in the final nucleus will be

(a)

$\frac{A-Z-4}{Z-2}$

(b)

$\frac{A-Z-2}{Z-6}$

(c)

$\frac{A-Z-4}{Z-6}$

(d)

$\frac{A-Z-12}{Z-4}$

5. A system consists of N0 nucleus at t=0. The number of nuclei remaining after half of a half-life (that is, at time t=$\frac{q}{2}T_\frac{1}{2}$)

(a)

$\frac{N_0}{2}$

(b)

$\frac{N_0}{\sqrt2}$

(c)

$\frac{N_0}{4}$

(d)

$\frac{N_0}{8}$

6. Bohr's postulate is based on

(a)

conservation of linear momentum

(b)

quantisation of angular momentum

(c)

conservation of quantum frequency

(d)

none of these

7. The ground state energy of hydrogen atom is 13.6 eV. The energy needed to ionize H2 atom from its second excited state.

(a)

1.51 eV

(b)

3.4 eV

(c)

13.6 eV

(d)

none

8. An alpha nucleus of energy 1/2 mv2 bombards a heavy nuclear target of charge Ze. Then the distance of closest approach for the alpha nucleus will be proportional to

(a)

v2

(b)

$\frac{1}{m}$

(c)

$\frac{1}{v^}$

(d)

$\frac{1}{Ze}$

9. The fig. represents the observed intensity of X-rays emitted by an X-ray tube as a function of wavelength. The sharp peaks A and B denote

(a)

continuous spectrum

(b)

band spectrum

(c)

characteristic spectrum

(d)

10. A beam of electron posses undeflected through mutually perpendicular electric and magnetic fields. If the electric field is switched off and the same magnetic field is maintained, the electrons move,

(a)

in a circular orbit

(b)

along a parabolic path

(c)

along a straight line

(d)

in an elliptical orbit

11. For first order X-ray diffraction, the wavelength in of the X-ray is equal to the lattice spacing at a glancing angle is

(a)

15°

(b)

60°

(c)

45°

(d)

30°

12. In the given nuclear fission reaction, 'X' denotes which particle?
92U235 + 0n1 56Ba141 + 36Kr92 + 3X + Q

(a)

electron

(b)

α -particle

(c)

neutron

(d)

neutrino

13. Elements having atomic number greater than ______ are radioactive.

(a)

48

(b)

68

(c)

88

(d)

83

14. Gamma rays are extensively used to destroy __________ affected cells

(a)

Sickle-cell anaemia

(b)

Cancer

(c)

HIV

(d)

Polio virus

15. Irene Curie and F. Joliot discovered ______ in the year 1934.

(a)

(b)

fluorescence

(c)

(d)

hydrogen bomb

16. Minimum size of a system in which at least 1 neutron is available for further fission is called __________

(a)

cut-off size

(b)

critical size

(c)

range of reactor

(d)

capability criteria

17. Pressurised heavy-water reactors in our country generally use _____ as fuel.

(a)

natural uranium oxide

(b)

(c)

titanium dioxide

(d)

plutonium

18. Graphite is used as a __________ in nuclear reactors.

(a)

moderator

(b)

coolant

(c)

detector

(d)

fuel

19. In a nuclear reactor, cadmium rods are used to _____________

(a)

speed up neutrons

(b)

slow down neutrons

(c)

absorb neutrons

(d)

remove heat

20. The explosion of hydrogen bomb is based on the principle of

(a)

uncontrolled fission reaction

(b)

nuclear fusion reaction

(c)

controlled fission

(d)

photo electric effect