CBSE Class 12 Physics Atoms Worksheet Set A

CBSE Class 12 Physics Atoms Worksheet Set A

Question. The ionization energy of Li⁺⁺ is equal to
(a) 9hcR
(b) 6hcR
(c) 2hcR
(d) hcR.

Answer: A

Question. The energy levels of the hydrogen spectrum is shown in figure. There are some transitions A, B, C, D and E. Transition A, B and C respectively represent 

(a) first member of Lyman series, third spectral line of Balmer series and the second spectral line of Paschen series
(b) ionization potential of hydrogen, second spectral line of Balmer series, third spectral line of Paschen series
(c) series limit of Lyman series, third spectral line of Balmer series and second spectral line of Paschen series
(d) series limit of Lyman series, second spectral line of Balmer series and third spectral line of Paschen series

Answer: C

Question. Taking Rydberg’s constant R_H = 1.097 × 10⁷m, first and second wavelength of Balmer series in hydrogen spectrum is
(a) 2000 Å, 3000 Å
(b) 1575 Å, 2960 Å
(c) 6529 Å, 4280 Å
(d) 6552 Å, 4863 Å

Answer: D

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

Answer: C

Question. The ionisation potential of H-atom is 13.6 V. When it is excited from ground state by monochromatic radiations of 970.6 Å, the number of emission lines will be (according to Bohr’s theory)
(a) 10
(b) 8
(c) 6
(d) 4

Answer: C

Question. Rutherford’s a-particle experiment showed that the atoms have
(a) Proton
(b) Nucleus
(c) Neutron
(d) Electrons

Answer: B

Question. Two H atoms in the ground state collide inelastically. The maximum amount by which their combined kinetic energy is reduced, is
(a) 10.20 eV
(b) 20.40 eV
(c) 13.6 eV
(d) 27.2 eV

Answer: A

Question. The ratio of the longest to shortest wavelengths in Brackett series of hydrogen spectra is
(a) 25/9
(b) 17/6
(c) 9/5
(d) 4/5

Answer: A

Question. In Rutherford scattering experiment, the number of α-particles scattered at 60° is 5 × 10⁶. The number of α-particles scattered at 120° will be
(a) 15 × 10⁶
(b) 3/5 x 10⁶
(c) 5/9 x 10⁶
(d) None of these

Answer: C

Question. The energy of He⁺ in the ground state is – 54.4 eV, then the energy of Li⁺⁺ in the first excited state will be
(a) – 30.6 eV
(b) 27.2 eV
(c) – 13.6 eV
(d) – 27.2 eV

Answer: A

Question. The wavelength of radiation is λ₀ when an electron jumps from third to second orbit of hydrogen atom. For the electron to jump from the fourth to the second orbit of the hydrogen atom, the wavelength of radiation emitted will be
(a) 16/25 λ₀
(b) 20/27 λ₀
(c) 27/20 λ₀
(d) 25/16 λ₀

Answer: B

Question. O₂ molecule consists of two oxygen atoms. In the molecule, nuclear force between the nuclei of the two atoms
(a) is not important because nuclear forces are short – ranged
(b) is as important as electrostatic force for binding the two atoms
(c) cancels the repulsive electrostatic force between the nuclei
(d) is not important because oxygen nucleus have equal number of neutrons and protons

Answer: A

Question. In the hydrogen atom, an electron makes a transition from n = 2 to n = 1. The magnetic field produced by the circulating electron at the nucleus
(a) decreases 16 times
(b) increases 4 times
(c) decreases 4 times
(d) increases 32 times

Answer: D

Question. One of the lines in the emission spectrum of Li²⁺ has the same wavelength as that of the 2^nd line of Balmer series in hydrogen spectrum. The electronic transition corresponding to this line is n = 12 → n = x. Find the value of x.
(a) 8
(b) 6
(c) 7
(c) 5

Answer: B

Question. The wavelength Kα of X-rays for two metals ‘A’ and ‘B’ are 4/1875R and 1/675R respectively, where ‘R’ is Rydberg constant. Find the number of elements lying between A and B according to their atomic numbers
(a) 3
(b) 1
(c) 4
(d) 5

Answer: C

Question. In the spectrum of hydrogen, the ratio of the longest wavelength in the Lyman series to the longest wavelength in the Balmer series is
(a) 9/4
(b) 27/5
(c) 5/27
(d) 4/9

Answer: D

Question. A hydrogen atom emits a photon corresponding to an electron transition from n = 5 to n = 1. The recoil speed of hydrogen atom is almost
(a) 10^–4 ms^–1
(b) 2 × 10^–2 ms^–1
(c) 4 ms^–1
(d) 8 × 10² ms^–1

Answer: C

Question. A hydrogen atom in its ground state absorbs 10.2 eV of energy. The orbital angular momentum is increased by
(a) 1.05 × 10^–34 J-s
(b) 3.16 × 10^–34 J-s
(c) 2.11 × 10^–34 J-s
(d) 4.22 × 10^–34 J-s

Answer: A

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. The spectral lines emitted by hydrogen atom according to Bohr’s theory will be
(a) one
(b) two
(c) three
(d) four

Answer: C

Question. The energy of electron in the nth orbit of hydrogen atom is expressed as En = -13.6/n²(eV) . The shortest and longest wavelength of Lyman series will be
(a) 910 Å, 1213 Å
(b) 5463 Å, 7858 Å
(c) 1315 Å, 1530 Å
(d) None of these

Answer: A

Question. The energy of a hydrogen atom in the ground state is – 13.6 eV. The energy of a He⁺ ion in the first excited state will be
(a) –13.6 eV
(b) – 27.2 eV
(c) – 54.4 eV
(d) – 6.8 eV

Answer: A

Question. A hydrogen atom is in ground state. Then to get six lines in emission spectrum, wavelength of incident radiation should be
(a) 800 Å
(b) 825 Å
(c) 975 Å
(d) 1025 Å

Answer: C

Question. Electrons in a certain energy level n = n₁, can emit 3 spectral lines. When they are in another energy level, n = n₂. They can emit 6 spectral lines. The orbital speed of the electrons in the two orbits are in the ratio of
(a) 4 : 3
(b) 3 : 4
(c) 2 : 1
(d) 1 : 2

Answer: A

Question. Which of the following statements are true regarding Bohr’s model of hydrogen atom?
(I) Orbiting speed of electron decreases as it shifts to discrete orbits away from the nucleus
(II) Radii of allowed orbits of electron are proportional to the principal quantum number
(III) Frequency with which electrons orbit around the nucleus in discrete orbits is inversely proportional to the cube of principal quantum number
(IV) Binding force with which the electron is bound to the nucleus increases as it shifts to outer orbits Select correct answer using the codes given below.
Codes :
(a) I and II
(b) II and IV
(c) I, II and III
(d) II, III and IV

Answer: A

Question. Consider the spectral line resulting from the transition n = 2→n = 1 in the atoms and ions given below. The shortest wavelength is produced by
(a) hydrogen atom
(b) deuterium atom
(c) singly ionized Helium
(d) doubly ionised Lithium

Answer: D

Question. If the atom ₁₀₀Fm²⁵⁷ follows the Bohr model and the radius of ₁₀₀Fm²⁵⁷ is n times the Bohr radius, then find n.
(a) 100
(b) 200
(c) 4
(d) 1/4

Answer: D

Question. Which of the following transitions in hydrogen atoms emit photons of highest frequency?
(a) n = 1 to n = 2
(b) n = 2 to n = 6
(c) n = 6 to n = 2
(d) n = 2 to n = 1

Answer: D

Question. For the ground state, the electron in the H – atom has an angular momentum = h, according to the simple Bohr model. Angular momentum is a vector and hence there will be infinitely many orbits with the vector pointing in all possible directions. In actuality, this is not true,
(a) because Bohr model gives in correct values of angular momentum
(b) because only one of these would have a minimum energy
(c) angular momentum must be in the direction of spin of electron
(d) because electrons go around only in horizontal orbits

Answer: A

Question. When an a-particle of mass 'm' moving with velocity 'v' bombards on a heavy nucleus of charge 'Ze', its distance of closest approach from the nucleus depends on m as : 
(a) 1/m
(b) 1/√m
(c) 1/m²
(d) m

Answer: A

Question. Doubly ionised helium atom and hydrogen ions are accelerated, from rest, through the same potential difference.
The ratio of final velocities of helium and hydrogen is
(a) 1 : √2
(b) √2 : 1
(c) 1 : 2
(d) 2 : 1

Answer: A

Question. 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) 1/Ze
(b) v2
(c) 1/m
(d) 1/v4

Answer: C

Question. Taking the Bohr radius as a₀ = 53 pm, the radius of Li⁺⁺ ion in its ground state, on the basis of Bohr's model, will be about
(a) 53 pm
(b) 27 pm
(c) 18 pm
(d) 13 pm

Answer: C

Question. Consider 3rd orbit of He+ (Helium), using non-relativistic approach, the speed of electron in this orbit will be [given K = 9 × 10⁹ constant, Z = 2 and h (Plank's Constant) = 6.6 × 10^–34 J s]
(a) 1.46 × 10⁶ m/s
(b) 0.73 × 10⁶ m/s
(c) 3.0 × 10⁸ m/s
(d) 2.92 × 10⁶ m/s

Answer: A

Question. Two particles of masses m₁, m₂ move with initial velocities u₁ and u₂. On collision, one of the particles get excited to higher level, after absorbing energy e. If final velocities of particles be v₁ and v₂ then we must have 

Answer: B

Question. The binding energy of a H – atom, considering an electron moving around a fixed nuclei (proton), is
B = -me⁴/8n²ε₀²h²(m = electron mass)
If one decides to work in a frame of reference where the electron is at rest, the proton would be moving around it.
By similar arguments, the binding energy would be
B = -me⁴/8n²ε₀²h²(m = proton mass) 
This last expression is not correct, because
(a) n would not be integral
(b) Bohr – quantisation applies only two electron
(c) the frame in which the electron is at rest is not inertial
(d) the motion of the proton would not be in circular orbits, even approximately.

Answer: C

Question. If in hydrogen atom, radius of nth Bohr orbit is r_n, frequency of revolution of electron in n^th orbit is f_n, choose the correct option.

Answer: D

Directions for : Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer from the following.
(a) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement -1
(b) Statement-1 is True, Statement -2 is True; Statement-2 is NOT a correct explanation for Statement - 1
(c) Statement-1 is True, Statement- 2 is False
(d) Statement-1 is False, Statement -2 is True

Question. Statement-1 : Bohr had to postulate that the electrons in stationary orbits around the nucleus do not radiate.
Statement-2 : According to classical physics all moving electrons radiate.

Answer: B

Question. Statement 1 : In Lyman series, the ratio of minimum and maximum wavelength is 3/4 .
Statement 2 : Lyman series constitute spectral lines corresponding to transition from higher energy to ground state of hydrogen atom.

Answer: B

Question. Statement-1 : Balmer series lies in the visible region of electromagnetic spectrum.
Statement-2 : 1/λ = R[1/22 - 1/n2] , where n = 3, 4, 5.

Answer: A

Question. Statement-1 : The force of repulsion between atomic nucleus and α-particle varies with distance according to inverse square law.
Statement-2 : Rutherford did a-particle scattering experiment.

Answer: B

Question. In Geiger-Marsden experiment, detection of scattered a-particles at a particular angle is done by
(a) counting flashes produced by a-particles on a ZnS coated screen
(b) counting spots produced on a photographic film
(c) using a galvanometer detector
(d) using a Geiger-counter

Answer : A

Question. Atoms consists of a positively charged nucleus is a consequence from the following observation of Geiger-Marsden experiment that
(a) most of a-particles do not pass straight through the gold foil
(b) very few a-particles scattered through an angle more than 90°
(c) very large number of a-particles are deflected by large angles
(d) None of the above

Answer : B

Question. If the orbital radius of the electron in a hydrogen atom is 4.7×10^-11 m. Compute the kinetic energy of the electron
in hydrogen atom.
(a) 15.3 eV
(b) - 15.3 eV
(c) 13.6 eV
(d) -13.6 eV

Answer : A

Question. The orbital radius of an electron in H-atom is increased by factor of 2, then the total energy of the electron will be
(a) decreased by 4
(b) increased by 2
(c) decreased by 2
(d) remain same

Answer : C

Question. An emission line spectrum is observed when
(a) a gas is excited by heating or by passing a electric discharge through it
(b) a gas is excited by applying pressure
(c) a gas under low pressure condition is excited by heating or by passing a electric discharge through it
(d) a gas under high pressure condition is excited by heating or by passing a electric discharge through it

Answer : C

Question. An electron of a hydrogen like atom is in excited state. If total energy of the electron is - 4.6 eV, then de-Broglie
wavelength of the electron is
(a) 6.27 nm
(b) 2.48 mm
(c) 0.57 nm
(d) 8 nm

Answer : C

Question. When white light is passed through an unexcited gas, then transmitted light consists of
(a) few bright lines in dark background
(b) few dark lines in bright background
(c) alternate dark and bright lines
(d) alternate dark and bright bands

Answer : B

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

Answer : C

Question. Rutherford’s atomic model could account for
I. concept of stationary orbits.
II. the positively charged central core of an atom.
III. origin of spectra.
IV. stability of atoms.
Choose the correct option from the codes given below.
(a) Only I
(b) Only II
(c) I, III and IV
(d) I, II, III and IV

Answer : B

Question. It is found experimentally that 13.6 eV energy is required to separate a hydrogen atom into a proton and an electron.
Then, the velocity of the electron in a hydrogen atom is
(a) 10¹⁵ m/s
(b) 2.2×10⁶ m/s
(c) 4.2×10⁸ m/s
(d) 3×10⁸ m/s

Answer : B

Question. The ratio of speed of an electron in ground state in Bohr’s first orbit of hydrogen atom to the velocity of light in air is
(a) e²/2πhc 
(b) 2eπ/hc
(c) e³/2πhck
(d) 2πe²k/hc

Answer : D

Question. The speed of an electron in ground state energy level is 2.6×10⁶ms^-1, then its speed in third excited state will be
(a) 5.6×10⁶ms^-1
(b) 6.5×10⁵ ms^-1
(c) 5.5×10⁵ ms^-1
(d) 4.3×10⁶ ms^-1

Answer : B

Question. The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the hydrogen atom, is
(a) 2 : - 1
(b) 1 : - 1
(c) 1 : 1
(d) 1 : - 2

Answer : B

Question. The total energy of an electron in an atom in an orbit is -3.4 eV. Its kinetic and potential energies are, respectively
(a) -3.4 eV, -6.8  eV
(b) 3.4 eV, -6.8 eV
(c) 3.4 eV, 3.4 eV
(d) - 3.4 eV, -3.4 eV

Answer : B

Question. If radius of first Bohr orbit is r,then the radius of second Bohr’s orbit will be
(a) 2r
(b) 8 r
(c) 4r
(d) 2 2r

Answer : C

Question. A 12.75 eV electron beam is used to bombard gaseous hydrogen at room temperature, then wavelengths emitted
are in
(a) either Paschen, Lyman or Balmer series
(b) either Brackett, Pfund or Lyman series
(c) either Paschen, Brackett or Balmer series
(d) either Lyman, Balmer or Brackett series

Answer : A

Question. The Bohr model for the spectra of a H-atom
(a) will not be applicable to hydrogen in the molecular form
(b) is applicable for multi-electron atom
(c) explain continuous as well as discrete spectral lines
(d) Both (a) and (b)

Answer : A

             Very Short Answer

Q1)       What is the full form of LASER?

Q2)       Who is credited for the discovery of the nucleus?

Q3)       Who discovered empirical formula?

Q4)       What is impact parameter?

Q5)       What is nucleus?

              Short Answer

Q6)       Define about electron orbits?

Q7)       What are atoms?

Q8)       What do you understand by Franck-Hertz experiment?

Q9)       How atomic hydrogen emits a line spectrum?

Q10)     What do you understand by the alpha-particle trajectory?

              Long Answer

Q11)     State the difference between kinetic energy and potential energy?

Q12)     Write short note on energy levels?

Q13)     What are the limitations of the Bohr’s model?

Q14)     Explain Rutherford’s Nuclear Model of Atom?

Q15)     Explain the Bohr model of the hydrogen atom?