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

12th Standard

Reg.No. :
•
•
•
•
•
•

Physics

Time : 00:20:00 Hrs
Total Marks : 20
20 x 1 = 20
1. In a hydrogen atom, the electron revolving in the fourth orbit, has angular momentum equal to

(a)

h

(b)

$\frac{h}{\pi}$

(c)

$\frac{4h}{\pi}$

(d)

$\frac{2h}{\pi}$

2. The electric potential between a proton and an electron is given by $V={ V }_{ 0 }in\left( \frac { r }{ { r }_{ 0 } } \right)$, where r0 is a constant. Assume that Bohr atom model is applicable of nth orbit rn with the principal quantum number n is

(a)

${ r }_{ n }\alpha \frac { 1 }{ n }$

(b)

${ r }_{ n }\alpha n$

(c)

${ r }_{ n }\alpha n\frac { 1 }{ { n }^{ 2 } }$

(d)

${ r }_{ n }\alpha { n }^{ 2 }$

3. The nucleus is approximately spherical in shape. Then the surface area of nucleus having mass number A varies as

(a)

A2/3

(b)

A4/3

(c)

A1/3

(d)

A5/3

4. The half-life period of a radioactive element A is same as the mean life time of another radioactive element B. Initially both have the same number of atoms. Then

(a)

A and B have the same decay rate initially

(b)

A and B decay at the same rate always

(c)

B will decay at faster rate than A

(d)

A will decay at faster rate than B.

5. The circumference of an electron's orbit of radius r must be an integral multiple of de Broglie wavelength that is

(a)

0.529 nl

(b)

$\sqrt nλ$

(c)

13.61

(d)

2ㅠr = nλ

6. In terms of Bohr radius a0, the radius of the third Bohr orbit of a hydrogen atom is given by

(a)

8ao

(b)

9ao

(c)

6ao

(d)

$\sqrt 3$ ao

7. The total energy of electrons in the ground state of hydrogen atom is -13.6 eV. The k.E of an electron in the first excited state is

(a)

6.8 eV

(b)

13.6 eV

(c)

1.7 eV

(d)

3.4 eV

8. The minimum wavelength. of the X-rays produced by electrons accelerated through a potential difference of V volts is directly proportional to

(a)

$\frac { 1 }{ \sqrt { V } }$

(b)

$\frac { 1 }{ V }$

(c)

$\sqrt { V }$

(d)

V2

9. J.J. Thomson's experiment demonstrated that

(a)

cathode rays are streams of negatively charged ions

(b)

all the mass of an atom is in the nucleus

(c)

specific charge of electrons is much greater than the protons.

(d)

e/m ratio changes when different gases is placed in the discharge tube

10. In a discharge tube, the source of positive rays is

(a)

cathode

(b)

anode

(c)

gas atoms present in the discharge tube

(d)

fluorescent screen

11. When an electric field is applied to an atom each of the spectral lines split into several lines. This effect is known as

(a)

Zeeman effect

(b)

Stark effect

(c)

Raman effect

(d)

Seebeck effect

12. In Millikan's experiment, the plates are kept at a distance of 16mm and are maintained at a poential difference of 10,000 V. The electric intensity is

(a)

62.5 V/m

(b)

6.25 x 105 V/m

(c)

6.25 x 103 V/m.

(d)

1.6 x 105 Vim

13. The wave number of a spectral line of hydrogen atom is equal to Rydberg's constant. The line is

(a)

first line of lyman series

(b)

series limit of lyman series

(c)

first line of pfund series

(d)

series limit of pfund sereis

14. Arrange the spectral lines Hα, Hβ, Hγ, Hδ in the increasing order of their wavelength

(a)

Hα, Hβ, H, Hδ

(b)

Hδ, H, Hβ, Hα

(c)

Hβ, Hα Hδ, H

(d)

Hα, Hβ, Hγ, Hδ

15. The direction of deflection shows that cathode rays are _________ in charge

(a)

negative

(b)

positive

(c)

neutral

(d)

oscillatory

16. In Millikan's experiment an oil drop of mass 4.9 x 10-14 kg is balanced by applying potential difference of 2 kV between the two plates which are 2 mm apart. The charge of the drop is ________________

(a)

1.96 x 10-18C

(b)

1.602 x 10-19C

(c)

12 C

(d)

4.9 x 10-19C

17. The orbits in which electrons supposed to be revolving according to Rutherford are ___________

(a)

square-shaped

(b)

circular

(c)

rectangular

(d)

linear

(a)

first

(b)

second

(c)

third

(d)

fourth

19. When the electron jumps from any of the outer orbits to the first orbit, spectral lines are emitted in the ________ region.

(a)

visible

(b)

IR

(c)

X-ray

(d)

UV

20. Paschen series of hydrogen atom comes under ___________ region.

(a)

IR

(b)

UV

(c)

X-ray

(d)

Gamma ray