CBSE Class 12 Physics Atoms Important Questions Worksheet

1 What is the cause for continuous EMR emitted by condensed matter and dense gases at all temperatures 

2 Give the difference between the radiation given out by condensed matter and rarefied gases heated in a flame.

3 What is nuclear model of atom?

4 Draw a neat labelled diagram showing the Geiger-Marsden scattering experiment. 

5 Show the graphical variation of Number of scattered particles detected with scattering angle obtained by Geiger-Marsden. 

6 Give the experimental results of Rutherford α-ray scattering experiment. 

7 What are α-particles?

8 Define impact parameter. 

9 Name the factor on which the trajectory traced out by a α-particle depends upon. What is its impact on the trajectory of the α-particle? 

10 Derive an expression to find the total energy of an electron in a hydrogen atom.

11 Give the significance of negative sign in the expression for total energy of an electron.

12 How do you identify a gas using emission line spectra?

13 Give the different spectral series emitted by Hydrogen atom. 

14 What are the draw backs of Rutherford model of atom?

15 Give the postulates of Bohr Model of atom

16 Derive an expression to find total energy of an electron in the nthorbit. 

17 How can you explain the quantized electron orbits and energy states of an atom?

Important Questions for NCERT Class 12 Physics Atoms

Question. Hydrogen atom in ground state is excited by a monochromatic radiation of l = 975 Å. Number of spectral lines in the resulting spectrum emitted will be
(a) 3
(b) 2
(c) 6
(d) 10 

Answer: C

Question. Electron in hydrogen atom first jumps from third excited state to second excited state and then from second excited to the first excited state. The ratio of the wavelengths l1 : l2 emitted in the two cases is
(a) 7/5
(b) 27/20
(c) 27/5
(d) 20/7 

Answer: D

Question. An electron of a stationary hydrogen atom passes from the fifth energy level to the ground level. The velocity that the atom acquired as a result of photon emission will be
(a) 24hR/25m
(b) 25hR/24m
(c) 25m/24hR
(d) 24m/25hR
(m is the mass of the electron, R Rydberg constant and h Planck’s constant)

Answer: A

Question. The transition from the state n = 3 to n = 1 in a hydrogen like atom results in ultraviolet radiation.
Infrared radiation will be obtained in the transition from
(a) 2 → 1
(b) 3 → 2
(c) 4 → 2
(d) 4 → 3 

Answer: D

Question. The ionization energy of the electron in the hydrogen atom in its ground state is 13.6 eV. The atoms are excited to higher energy levels to emit radiations of 6 wavelengths. Maximum wavelength of emitted radiation corresponds to the transition between
(a) n = 3 to n = 1 states
(b) n = 2 to n = 1 states
(c) n = 4 to n = 3 states
(d) n = 3 to n = 2 states

Answer: C

Question. What is the energy of photon whose wavelength is 6840 Å? 
(a) 1.81 eV
(b) 3.6 eV
(c) –13.6 eV
(d) 12.1 eV

Answer: A

Question. The ratio of the energy of the photon emitted by the ka line to that of the kb line is 
(a) greater than 1
(b) Less than 1
(c) 1
(d) indeterminate

Answer: B

Question. Ionization potential of hydrogen atom is 13.6 eV.
Hydrogen atoms in the ground state are excited by monochromatic radiation of photon energy 12.1 eV. According to Bohr’s theory, the spectral lines emitted by hydrogen will be
(a) one
(b) two
(c) three
(d) four.

Answer: C

Question. Maximum frequency of emission is obtained for the transition
(a) n = 2 to n = 1
(b) n = 6 to n = 2
(c) n = 1 to n = 2
(d) n = 2 to n = 6 

Answer: A

Question. When an electron does transition from n = 4 to n = 2, then emitted line spectrum will be
(a) first line of Lyman series
(b) second line of Balmer series
(c) first line of Paschen series
(d) second line of Paschen series. 

Answer: B

Question. An electron makes a transition from orbit n = 4 to the orbit n = 2 of a hydrogen atom. What is the wavelength of the emitted radiations?(R = Rydberg’s constant)
(a) 16/4R
(b) 16/5R
(c) 16/2R
(d) 16/3R

Answer: D

Question. Hydrogen atoms are excited from ground state of the principle quantum number 4. Then the number of spectral lines observed will be
(a) 3
(b) 6
(c) 5
(d) 2

Answer: B

Question. Consider an electron in the nth orbit of a hydrogen atom in the Bohr model. The circumference of the orbit can be expressed in terms of de Broglie wavelength l of that electron as
(a) (0.529)nλ
(b) nλ
(c) (13.6)λ
(d) nλ

Answer: D

Question. The interplanar distance in a crystal is 2.8 × 10^–8 m. The value of maximum wavelength which can be diffracted
(a) 2.8 × 10^–8 m
(b) 5.6 × 10^–8 m
(c) 1.4 × 10^–8 m
(d) 7.6 × 10^–8 m 

Answer: B

Question. The minimum wavelength of the X-rays produced by electrons accelerated through a potential difference of V volts is directly proportional to
(a) 1/√V
(b) 1/V
(c) √V
(d) V²

Answer: B

Question. If the electron in hydrogen orbit jumps from third orbit to second orbit, the wavelength of the emitted radiation is given by : 
(a) λ=R/6
(b) λ=5/R
(c) λ= 36/5R
(d) λ= 5R36

Answer: C

Question. The radius of hydrogen atom in the first excited level is :
(a) twice
(b) four times
(c) same
(d) half

Answer: B

Question. According to Bohr’s model of hydrogen atom
(a) the linear velocity of the electron is quantised.
(b) the angular velocity of the electron is quantised.
(c) the linear momentum of the electron is quantised.
(d) the angular momentum of the electron is quantised.

Answer: D

Question. The ratio between Bohr radii is
(a) 1 : 2 : 3
(b) 2 : 4 : 6
(c) 1 : 4 : 9
(d) 1 : 3 : 5

Answer: A

Question. The ratio of wavelengths of the last line of Balmer series and the last line of Lyman series is :-
(a) 1
(b) 4
(c) 0.5
(d) 2 

Answer: B

Question. The first line of Balmer series has wavelength 6563 Å. What will be the wavelength of the first member of Lyman series
(a) 1215.4 Å
(b) 2500 Å
(c) 7500 Å
(d) 600 Å

Answer: A

Question. In a hydrogen atom following the Bohr’s postulates the product of linear momentum and angular momentum is proportional to (n)x where ‘n’ is the orbit number. Then ‘x’ is
(a) 0
(b) 2
(c) –2
(d) 1

Answer: A

Question. In an atom, the two electrons move round the nucleus in circular orbits of radii R and 4R. The ratio of the time taken by them to complete one revolution is
(a) 1/4
(b) 4/1
(c) 8/1
(d) 1/8

Answer: D

Question. The ratio of the energies of the hydrogen atom in its first to second excited states is
(a) 1/4
(b) 4/9
(c) 9/4
(d) 4

Answer: C

Question. For the principal quantum number n = 4, the total number of different possible values of the azimuthal quantum number l, is
(a) 2
(b) 8
(c) 4
(d) 3

Answer: C

Question. With increasing quantum number, the energy difference between adjacent energy levels in atoms
(a) decreases
(b) increases
(c) remains constant
(d) decreases for low Z and increases for high Z

Answer: A

Question. The angular momentum of the electron in hydrogen atom in the ground state is
(a) 2h
(b) h/2
(c) h/2π
(d) h/4π

Answer: C

Question. If e is electronic charge, the equivalent current for an electron revolving with a frequency n in the ground state of hydrogen atom is
(a) 2πne
(b) e/πn
(c) e/2πn
(d) en

Answer: D

Question. The principle of LASER action involves
(a) amplification of particular frequency emitted by the system
(b) population inversion
(c) stimulated emissin
(d) All of the above.

Answer: D

Question. In which of the following series, does the 121.5 nm line of the spectrum of the hydrogen atom lie ?
(a) Lyman series
(b) Balmer series
(c) Paschen series
(d) Brackett series.

Answer: A

Question. For the azimuthal quantum number l = 3, the total number of different possible values of the magnetic azimuthal quantum number m1, is
(a) 3
(b) 4
(c) 5
(d) 7

Answer: D

Question. The simple Bohr model cannot be directly applied to calculate the energy levels of an atom with many electrons.
This is because
(a) of the electrons not being subject to a central force
(b) of the electrons colliding with each other
(c) of screening effects
(d) the force between the nucleus and an electron will no longer be given by Coulomb's law

Answer: A

Question. The kinetic energy of the electorn in an orbit of radius r in hydrogen atom is (e = electronic charge)
(a) e²/r²
(b) e²/2r
(c) e²/r
(d) e²/2r²

Answer: B

Question. An electron in hydrogen atom makes a transition n₁ → n₂ where n₁ and n₂ are principal quantum numbers of the two states. Assuming Bohr’s model to be valid the time period of the electron in the initial state is eight times that in the final state. The possible values of n₁ and n₂ are
(a) n₁ = 4 and n₂ = 2 
(b) n₁ = 6 and n₂ = 2
(c) n₁ = 8 and n₂ = 1
(d) n₁ = 8 and n₂ = 2

Answer: A

Question. According to the Rutherford’s atomic model, the electrons inside the atom are
(a) stationary
(b) not stationary
(c) centralized
(d) None of these

Answer: B

Question. According to classical theory, the circular path of an electron in Rutherford atom is
(a) spiral
(b) circular
(c) parabolic
(d) straight line

Answer: A

Question. Hydrogen atom excites energy level from fundamental state to n = 3. Number of spectral lines according to Bohr, is
(a) 4
(b) 3
(c) 1
(d) 2

Answer: B