Download JEE MCQs for JEE Physics: Atoms
Access targeted multiple-choice questions for Atoms designed to align with the latest JEE academic syllabus for JEE Physics. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.
Chapter-wise Objective Questions: Atoms
Navigate directly to the 50 objective questions for Atoms using the digital viewer below. Each practice set includes verified answer keys, allowing students to instantly cross-check their work and identify areas requiring further revision.
Multiple Choice Questions
(a) 1.7 Å
(b) 3.3 Å
(c) 0.53 Å
(d) 6.6 Å
Show Answer & Explanation
Answer: (b) 3.3 Å
Explanation:
1. Bohr's condition \( 2\pi r_n=n\lambda \) gives for \( n=1 \): \( \lambda=2\pi r_1=2\pi\times0.53=3.3\text{ Å} \).
Teacher's Note:
1. The first orbit holds exactly one de Broglie wavelength.
2. The wavelength equals the circumference of the orbit.
(a) \( \text{Li}^{2+} \)
(b) \( \text{Be}^{3+} \)
(c) \( \text{H} \)
(d) \( \text{He}^+ \)
Show Answer & Explanation
Answer: (d) \( \text{He}^+ \)
Explanation:
1. Ionisation energy \( =\dfrac{12400}{228}=54.4\text{ eV} \).
2. Since \( 13.6Z^2=54.4 \), \( Z=2 \): the ion is \( \text{He}^+ \).
Teacher's Note:
1. Ionisation energy is Z squared times 13.6 eV.
2. The threshold wavelength is the longest wavelength that can ionise.
(a) \( 1.05\times10^4\text{ K} \)
(b) \( 2.1\times10^5\text{ K} \)
(c) \( 1.05\times10^5\text{ K} \)
(d) \( 3.5\times10^5\text{ K} \)
Show Answer & Explanation
Answer: (c) \( 1.05\times10^5\text{ K} \)
Explanation:
1. \( T=\dfrac{2E}{3k}=\dfrac{2\times13.6\times1.6\times10^{-19}}{3\times1.38\times10^{-23}}\approx1.05\times10^5\text{ K} \).
Teacher's Note:
1. Convert the energy to joules.
2. This temperature shows why hydrogen is ionised in stars.
(a) 912 Å and 228 Å
(b) 1215 Å and 304 Å
(c) 912 Å and 456 Å
(d) 228 Å and 912 Å
Show Answer & Explanation
Answer: (a) 912 Å and 228 Å
Explanation:
1. The smallest wavelength is the series limit of the Lyman series, \( \dfrac1\lambda=RZ^2 \).
2. For hydrogen \( \lambda=\dfrac{12400}{13.6}=912\text{ Å} \); for \( \text{He}^+ \) \( \lambda=\dfrac{912}{4}=228\text{ Å} \).
Teacher's Note:
1. The most energetic photon corresponds to a transition from infinity to the ground state.
2. Wavelength scales as one over Z squared.
(a) \( 4.1\times10^{16}\text{ rad/s} \)
(b) \( 1.0\times10^{16}\text{ rad/s} \)
(c) \( 2.1\times10^{15}\text{ rad/s} \)
(d) \( 2.1\times10^{16}\text{ rad/s} \)
Show Answer & Explanation
Answer: (d) \( 2.1\times10^{16}\text{ rad/s} \)
Explanation:
1. Speed \( v=2.19\times10^6\dfrac{Z}{n}=2.19\times10^6\text{ m/s} \) and radius \( r=\dfrac{n^2a_0}{Z}=1.06\times10^{-10}\text{ m} \).
2. \( \omega=\dfrac vr=\dfrac{2.19\times10^6}{1.06\times10^{-10}}=2.1\times10^{16}\text{ rad/s} \).
Teacher's Note:
1. Both the speed and the radius have simple Z and n dependence in Bohr's model.
2. omega is proportional to Z squared over n cubed.
(a) 33 m/s
(b) 3.3 m/s
(c) 0.33 m/s
(d) 3.3 km/s
Show Answer & Explanation
Answer: (b) 3.3 m/s
Explanation:
1. Photon energy \( 10.2\text{ eV} \) and momentum \( \dfrac Ec=\dfrac{10.2\times1.6\times10^{-19}}{3\times10^8}=5.4\times10^{-27}\text{ kg m/s} \).
2. By momentum conservation \( v=\dfrac{p}{m}=\dfrac{5.4\times10^{-27}}{1.67\times10^{-27}}=3.3\text{ m/s} \).
Teacher's Note:
1. The recoil momentum equals the photon momentum.
2. Recoil energy is a tiny fraction of the photon energy.
(a) 114 Å and 3 lines
(b) 114 Å and 6 lines
(c) 228 Å and 3 lines
(d) 912 Å and 3 lines
Show Answer & Explanation
Answer: (a) 114 Å and 3 lines
Explanation:
1. Energy required \( 13.6\times9\left(1-\dfrac19\right)=108.8\text{ eV} \), so \( \lambda=\dfrac{12400}{108.8}=114\text{ Å} \).
2. From \( n=3 \) the possible transitions are 3 to 2, 3 to 1 and 2 to 1: three lines.
Teacher's Note:
1. The number of lines from level n is n(n-1)/2.
2. Use Z = 3 for lithium.
(a) 10.2 eV
(b) 13.6 eV
(c) 20.4 eV
(d) 27.2 eV
Show Answer & Explanation
Answer: (c) 20.4 eV
Explanation:
1. In a perfectly inelastic head-on collision of equal masses, half of the kinetic energy can be lost: \( \Delta K=\dfrac K2 \).
2. The smallest excitation energy is 10.2 eV, so \( \dfrac K2=10.2 \) and \( K=20.4\text{ eV} \).
Teacher's Note:
1. The kinetic energy of the centre of mass cannot be used for excitation.
2. The reduced mass gives half of the energy for equal masses.
(a) 0.62 Å; 0.89 Å, 2.95 Å, 9.84 Å
(b) 0.31 Å; 0.89 Å, 2.95 Å, 9.84 Å
(c) 0.31 Å; 0.62 Å, 2.95 Å, 9.84 Å
(d) 0.31 Å; 0.89 Å, 1.77 Å, 4.4 Å
Show Answer & Explanation
Answer: (b) 0.31 Å; 0.89 Å, 2.95 Å, 9.84 Å
Explanation:
1. Cut-off wavelength \( \lambda_{min}=\dfrac{12400}{40000}=0.31\text{ Å} \).
2. At 20 kV: first photon \( 0.7\times20=14\text{ keV} \) (\( 0.89\text{ Å} \)); the electron keeps 6 keV, so the second photon is \( 0.7\times6=4.2\text{ keV} \) (\( 2.95\text{ Å} \)); it keeps 1.8 keV and the third is \( 1.26\text{ keV} \) (\( 9.84\text{ Å} \)).
Teacher's Note:
1. Each collision takes 70% of the remaining energy.
2. Wavelength in Å is 12.4 divided by the energy in keV.
(a) 173 pm
(b) 215 pm
(c) 193 pm
(d) 154 pm
Show Answer & Explanation
Answer: (d) 154 pm
Explanation:
1. Moseley's law: \( \dfrac1\lambda\propto(Z-1)^2 \).
2. \( \lambda_{Cu}=193\left(\dfrac{25}{28}\right)^2=154\text{ pm} \).
Teacher's Note:
1. Subtract 1 from each atomic number.
2. A heavier element has a shorter wavelength.
(a) n = 5, Z = 3
(b) n = 6, Z = 2
(c) n = 6, Z = 3
(d) n = 4, Z = 3
Show Answer & Explanation
Answer: (c) n = 6, Z = 3
Explanation:
1. From \( n \) to 2: \( 27.2\text{ eV} \); from \( n \) to 3: \( 10.2\text{ eV} \). The difference is \( E_3-E_2=17.0\text{ eV} \).
2. \( 13.6Z^2\left(\dfrac14-\dfrac19\right)=17\Rightarrow Z^2=9 \), so \( Z=3 \).
3. Then \( 122.4\left(\dfrac14-\dfrac1{n^2}\right)=27.2\Rightarrow n=6 \).
Teacher's Note:
1. Subtracting the two energy totals isolates the 3-to-2 transition.
2. Use Z-squared times 13.6 eV for the energy scale.
(a) 79.0 eV
(b) 49.2 eV
(c) 38.2 eV
(d) 51.8 eV
Show Answer & Explanation
Answer: (a) 79.0 eV
Explanation:
1. Removing the second electron means ionising He\( ^+ \): \( 13.6\times Z^2=13.6\times4=54.4\text{ eV} \).
2. Total \( 24.6+54.4=79.0\text{ eV} \).
Teacher's Note:
1. The first and second ionisation energies add.
2. The second electron sees Z = 2 with a single electron.
(a) 1640 Å
(b) 2430 Å
(c) 4687 Å
(d) 1215 Å
Show Answer & Explanation
Answer: (d) 1215 Å
Explanation:
1. Hydrogen first Balmer line (3 to 2): \( \dfrac1{\lambda_H}=R\left(\dfrac14-\dfrac19\right)=\dfrac{5R}{36} \).
2. He\( ^+ \) second line of its Balmer series (4 to 2): \( \dfrac1{\lambda}=4R\left(\dfrac14-\dfrac1{16}\right)=\dfrac{3R}{4} \).
3. Ratio \( \dfrac{\lambda}{\lambda_H}=\dfrac{5/36}{3/4}=\dfrac5{27} \), so \( \lambda=6561\times\dfrac5{27}=1215\text{ Å} \).
Teacher's Note:
1. The Balmer series ends at n = 2 for any hydrogen-like ion.
2. The factor Z squared multiplies the Rydberg term.
(a) \( \lambda'=\lambda,\ \nu'=\nu \)
(b) \( \lambda'>\lambda,\ \nu'<\nu \)
(c) \( \lambda'<\lambda,\ \nu'>\nu \)
(d) \( \lambda'>\lambda,\ \nu'>\nu \)
Show Answer & Explanation
Answer: (b) \( \lambda'>\lambda,\ \nu'<\nu \)
Explanation:
1. The electron recoils and gains kinetic energy, taken from the photon.
2. The photon therefore has less energy: lower frequency and longer wavelength (Compton effect).
Teacher's Note:
1. Energy and momentum are conserved in the collision.
2. The wavelength shift is \( \Delta\lambda=\dfrac{h}{mc}(1-\cos\theta) \).
(a) 4
(b) 3
(c) 5
(d) 6
Show Answer & Explanation
Answer: (a) 4
Explanation:
1. \( \dfrac1\lambda=\tfrac34R(Z-1)^2 \). For A: \( \dfrac{1875R}{4}=\dfrac{3R}{4}(Z-1)^2\Rightarrow(Z-1)^2=625 \), so \( Z=26 \).
2. For B: \( 675R=\dfrac{3R}{4}(Z-1)^2\Rightarrow(Z-1)^2=900 \), so \( Z=31 \).
3. Elements between: 27, 28, 29, 30, that is 4.
Teacher's Note:
1. Use the K-alpha Moseley relation with screening constant 1.
2. Count only the elements strictly between the two.
(a) 0.15 eV
(b) 15 eV
(c) 1.5 eV
(d) 1.5 keV
Show Answer & Explanation
Answer: (c) 1.5 eV
Explanation:
1. \( K=1240\left(\dfrac1{180}-\dfrac1{230}\right)=6.89-5.39=1.5\text{ eV} \).
Teacher's Note:
1. The kinetic energy is the photon energy minus the work function.
2. The work function is hc divided by the threshold wavelength.
(a) 1.05 kV
(b) 2.56 kV
(c) 5.68 kV
(d) 517 V
Show Answer & Explanation
Answer: (b) 2.56 kV
Explanation:
1. \( eV=\tfrac12mv^2=\tfrac12\times9.1\times10^{-31}\times(3\times10^7)^2=4.1\times10^{-16}\text{ J} \).
2. \( V=\dfrac{4.1\times10^{-16}}{1.6\times10^{-19}}\approx2.56\text{ kV} \).
Teacher's Note:
1. At 10% of c the non-relativistic formula is accurate to better than 1%.
2. The potential difference equals kinetic energy in eV.
(a) (1), (3) and (4) only
(b) (2), (3) and (4) only
(c) (1), (2) and (3) only
(d) (1), (2) and (4) only
Show Answer & Explanation
Answer: (d) (1), (2) and (4) only
Explanation:
1. Longest wavelength is \( p=2 \): \( \dfrac{1500\times4}{3}=2000\text{ Å} \); shortest is as \( p\to\infty \): 1500 Å. So (1) is true.
2. The photon energy limit is \( \dfrac{12400}{1500}=8.27\text{ eV} \), the ionisation energy (4) is true; \( E_n=-\dfrac{8.27}{n^2} \).
3. \( E_4-E_3=8.27\left(\dfrac19-\dfrac1{16}\right)=0.40\text{ eV} \) (2) is true, while \( E_2=-2.07\text{ eV} \) so (3) is false.
Teacher's Note:
1. Work out the energy levels from the series limit.
2. The second orbit energy is negative and smaller in magnitude than 6.2 eV.
(a) (1), (2) and (3) only
(b) (2), (3) and (4) only
(c) (1), (2), (3) and (4)
(d) (1) and (4) only
Show Answer & Explanation
Answer: (c) (1), (2), (3) and (4)
Explanation:
1. Photon energy \( \dfrac{12400}{975}=12.7\text{ eV} \) raises the atom to \( n=4 \) (\( 13.6\left(1-\dfrac1{16}\right)=12.75\text{ eV} \)).
2. From \( n=4 \) there are \( \dfrac{4\times3}{2}=6 \) lines. \( E_4-E_3=13.6\left(\dfrac19-\dfrac1{16}\right)=0.66\text{ eV} \).
3. Longest wavelength is 4 to 3: \( \dfrac{12400}{0.66}=18800\text{ Å}=1.88\ \mu\text{m} \); the shortest is 4 to 1, which is the 975 Å photon. All four are correct.
Teacher's Note:
1. Count the lines using n(n-1)/2.
2. The transition 4 to 1 has the same energy as the absorbed photon.
(a) \( \dfrac1{n^3} \)
(b) \( \dfrac1{n^2} \)
(c) \( n^2 \)
(d) \( \dfrac1{n^4} \)
Show Answer & Explanation
Answer: (a) \( \dfrac1{n^3} \)
Explanation:
1. \( \nu\propto\dfrac1{(n-1)^2}-\dfrac1{n^2}=\dfrac{2n-1}{n^2(n-1)^2}\approx\dfrac{2}{n^3} \) for large \( n \).
Teacher's Note:
1. For large n the frequency equals the orbital frequency, as the correspondence principle requires.
2. Orbital frequency goes as one over n cubed.
(a) \( \dfrac78 \)
(b) \( \dfrac9{20} \)
(c) \( \dfrac{20}{9} \)
(d) \( \dfrac87 \)
Show Answer & Explanation
Answer: (d) \( \dfrac87 \)
Explanation:
1. Photon energies: \( 13.6+1.8=15.4\text{ eV} \) and \( 13.6+4.0=17.6\text{ eV} \).
2. \( \dfrac{\lambda_1}{\lambda_2}=\dfrac{E_2}{E_1}=\dfrac{17.6}{15.4}=\dfrac87 \).
Teacher's Note:
1. The ionisation energy of hydrogen is 13.6 eV.
2. Wavelength is inversely proportional to photon energy.
(a) \( 10^{-15}\text{ cm} \)
(b) \( 10^{-10}\text{ cm} \)
(c) \( 10^{-12}\text{ cm} \)
(d) \( 1\text{ Å} \)
Show Answer & Explanation
Answer: (c) \( 10^{-12}\text{ cm} \)
Explanation:
1. \( K=\dfrac{1}{4\pi\epsilon_0}\dfrac{(2e)(92e)}{r_0} \), so \( r_0=\dfrac{9\times10^9\times184\times(1.6\times10^{-19})^2}{5\times10^6\times1.6\times10^{-19}}=5.3\times10^{-14}\text{ m}\approx5\times10^{-12}\text{ cm} \).
Teacher's Note:
1. At the closest approach all the kinetic energy has become electric potential energy.
2. The result is far larger than the nuclear radius (a few fermi).
(a) (2) and (4) only
(b) (1) and (3) only
(c) (1) and (4) only
(d) (2) and (3) only
Show Answer & Explanation
Answer: (b) (1) and (3) only
Explanation:
1. Angular momentum \( n\dfrac{h}{2\pi} \) gives \( n=3 \). \( r=\dfrac{n^2a_0}{Z}=4.5a_0 \) gives \( Z=2 \) (He\( ^+ \)).
2. From \( n=3 \): \( 3\to1:\ \dfrac1\lambda=4R\left(1-\dfrac19\right)=\dfrac{32R}{9} \), so \( \lambda=\dfrac{9}{32R} \).
3. \( 3\to2:\ \dfrac1\lambda=4R\left(\dfrac14-\dfrac19\right)=\dfrac{5R}{9} \), so \( \lambda=\dfrac9{5R} \); and \( 2\to1:\ \lambda=\dfrac{1}{3R} \). So (1) and (3) occur.
Teacher's Note:
1. Find n from the angular momentum and Z from the radius.
2. List all possible transitions from the level.
(a) He\( ^+ \) and 63.75 eV
(b) Li\( ^{2+} \) and 63.75 eV
(c) He\( ^+ \) and 51 eV
(d) D and 54.4 eV
Show Answer & Explanation
Answer: (a) He\( ^+ \) and 63.75 eV
Explanation:
1. Six lines mean the ions reach \( n=4 \). The line \( \lambda=121.6\text{ nm} \) has energy \( 10.2\text{ eV} \); for \( Z=2 \): \( 54.4\left(\dfrac14-\dfrac1{16}\right)=10.2\text{ eV} \) (4 to 2), so the gas is He\( ^+ \).
2. Excitation energy \( 54.4\left(1-\dfrac1{16}\right)=51\text{ eV} \). In an inelastic collision with the ion (mass 4 times the neutron mass) only the fraction \( \dfrac{M}{m+M}=\dfrac45 \) of the neutron energy is available: \( K=\dfrac{51}{0.8}=63.75\text{ eV} \).
Teacher's Note:
1. Only energy in the centre-of-mass frame can excite the ion.
2. Six lines correspond to four levels.
(a) 802 nm
(b) 1882 nm
(c) 1648 nm
(d) 823 nm
Show Answer & Explanation
Answer: (d) 823 nm
Explanation:
1. The 122 nm line is the first Lyman line: \( \dfrac1{122}=\dfrac{3R}{4} \), so \( R=\dfrac{1}{91.5}\text{ nm}^{-1} \).
2. The infrared region begins with the Paschen series, whose smallest wavelength is its limit: \( \dfrac1\lambda=\dfrac R9 \), so \( \lambda=9\times91.5=823\text{ nm} \).
Teacher's Note:
1. The Paschen series (n = 3) is the first in the infrared.
2. The smallest wavelength of a series is its series limit.
Free study material for Physics
Download Chapter MCQs: JEE Physics Atoms
About Atoms MCQs for JEE Physics
Review structured objective questions for JEE Physics Atoms. Built according to official JEE guidelines, these MCQ sets support daily revision and core concept reinforcement.
How to Verify Your MCQ Answers
Built using the official NCERT book for JEE, these Physics objective sets provide reliable academic guidance. Pair your practice with our recommended NCERT solutions to master optimal problem-solving approaches.
Enhance Speed with Online MCQ Tests
Follow up your worksheet practice by attempting the interactive online Physics MCQ test for this chapter to evaluate your execution speed. All platform resources are free to access.
FAQs
You can get most exhaustive JEE Physics Atoms MCQs Set 13 for free on StudiesToday.com. These MCQs for JEE Physics are updated for the 2026-27 academic session as per JEE examination standards.
Yes, our JEE Physics Atoms MCQs Set 13 include the latest type of questions, such as Assertion-Reasoning and Case-based MCQs. 50% of the JEE paper is now competency-based.
By solving our JEE Physics Atoms MCQs Set 13, JEE students can improve their accuracy and speed which is important as objective questions provide a chance to secure 100% marks in the Physics.
Yes, Physics MCQs for JEE have answer key and brief explanations to help students understand logic behind the correct option as its important for 2026 competency-focused JEE exams.
Yes, you can also access online interactive tests for JEE Physics Atoms MCQs Set 13 on StudiesToday.com as they provide instant answers and score to help you track your progress in Physics.