ATOMIC PHYSICS Test (CDS & AFCAT)

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• 0 Questions answered incorrect
• 25 Questions unattempted

• 1

  1. Which of the following is NOT a fundamental particle of an atom?

   

  • A

    (a) Electron
     

  • B

    (b) Proton
     

  • C

    (c) Neutron
     

  • D

    (d) Molecule

  Explanation

  ? Explanation: Electron, proton, and neutron are subatomic particles. Molecule is formed by the combination of two or more atoms.

• 2

  2. Who discovered the neutron?

   

  • A

    (a) Rutherford
     

  • B

    (b) J. J. Thomson
     

  • C

    (c) James Chadwick
     

  • D

    (d) Niels Bohr

  Explanation

  ? Explanation: Neutron was discovered by James Chadwick in 1932.

• 3

  3. According to Bohr’s model, electrons revolve around the nucleus —

   

  • A

    (a) in elliptical paths
     

  • B

    (b) in circular orbits of fixed energy
     

  • C

    (c) without losing energy

  • D

    (d) (b) and (c) both 

  Explanation

  ? Explanation: In Bohr’s model, electrons move in discrete circular orbits with fixed energy levels and do not radiate energy while revolving.

• 4

  4. The atom is mostly —

   

  • A

    (a) solid
     

  • B

    (b) empty space
     

  • C

    (c) filled with electrons
     

  • D

    (d) filled with neutrons

  Explanation

  ? Explanation: Rutherford’s experiment proved that most of the atom’s volume is empty space; only a tiny nucleus exists at the center.

• 5

  5. The mass of an atom is mainly due to —

   

  • A

    (a) electrons only
     

  • B

    (b) protons and neutrons
     

  • C

    (c) protons and electrons
     

  • D

    (d) neutrons and electrons

  Explanation

  ? Explanation: Electrons have negligible mass. The atomic mass comes from protons + neutrons (called nucleons).

• 6

  6. The number of protons in an atom is equal to —

   

  • A

    (a) Atomic weight
     

  • B

    (b) Atomic number
     

  • C

    (c) Mass number
     

  • D

    (d) Neutron number

  Explanation

  ? Explanation: Atomic number (Z) = Number of protons = Number of electrons (in a neutral atom).

• 7

  7. Isotopes of an element have —

   

  • A

    (a) Same atomic number but different mass numbers
     

  • B

    (b) Different atomic number but same mass number
     

  • C

    (c) Same number of neutrons
     

  • D

    (d) Same chemical properties

  Explanation

  ? Explanation: Isotopes have same number of protons (Z) → same chemical behavior, but different neutrons → different masses.

• 8

  8. Isobars are atoms which have —

   

  • A

    (a) Same mass number but different atomic numbers
     

  • B

    (b) Same atomic number but different mass numbers
     

  • C

    (c) Same number of neutrons
     

  • D

    (d) Same electrons

  Explanation

  ? Explanation: Example: Argon-40 and Calcium-40 → same A (40) but different Z.

• 9

  9. The nucleus of an atom contains —

   

  • A

    (a) Protons only
     

  • B

    (b) Protons and electrons
     

  • C

    (c) Protons and neutrons
     

  • D

    (d) Electrons only

  Explanation

  ? Explanation: Nucleus = protons + neutrons (collectively called nucleons).

• 10

  10. Which of the following forces binds nucleons together in a nucleus?

   

  • A

    (a) Gravitational force
     

  • B

    (b) Magnetic force
     

  • C

    (c) Nuclear force
     

  • D

    (d) Electrostatic force

  Explanation

  ? Explanation: Nuclear force is a strong short-range attractive force that binds protons and neutrons together.

• 11

  11. The nuclear force is —

   

  • A

    (a) Stronger than the Coulomb force
     

  • B

    (b) Independent of electric charge
     

  • C

    (c) Acts equally between p–p, n–n, p–n
     

  • D

    (d) All of the above

  Explanation

  ? Explanation: Nuclear force is very strong, charge independent, and acts uniformly among all nucleon pairs.

• 12

  12. Radioactivity is the phenomenon of —

   

  • A

    (a) Emission of alpha, beta, and gamma rays
     

  • B

    (b) Chemical reaction
     

  • C

    (c) Ionization of atoms
     

  • D

    (d) Splitting of nucleus by force

  Explanation

  ? Explanation: Radioactivity = spontaneous disintegration of unstable nuclei emitting α, β, γ radiations.

• 13

  13. Alpha particles carry —

   

  • A

    (a) +1 charge
     

  • B

    (b) +2 charge
     

  • C

    (c) -1 charge
     

  • D

    (d) No charge

  Explanation

  ? Explanation: Alpha particle = Helium nucleus (2 protons + 2 neutrons), hence +2 charge.

• 14

  14. Beta particles are —

   

  • A

    (a) Helium nuclei
     

  • B

    (b) Electrons
     

  • C

    (c) Neutrons
     

  • D

    (d) Gamma rays

  Explanation

  ? Explanation: Beta rays are high-speed electrons emitted from the nucleus during decay.

• 15

  15. Gamma rays are —

   

  • A

    (a) Charged particles
     

  • B

    (b) Neutral electromagnetic waves
     

  • C

    (c) Positively charged
     

  • D

    (d) Negatively charged

  Explanation

  ? Explanation: Gamma rays are neutral electromagnetic radiations of very high energy.

• 16

  16. Arrange the following radiations in increasing order of energy:

   

  • A

    (a) Alpha < Beta < Gamma
     

  • B

    (b) Beta < Gamma < Alpha
     

  • C

    (c) Gamma < Beta < Alpha
     

  • D

    (d) Alpha < Gamma < Beta

  Explanation

  ? Explanation: Alpha (least energy) → Beta → Gamma (highest energy).

• 17

  17. The half-life of Carbon-14 is —

   

  • A

    (a) 573 years
     

  • B

    (b) 5730 years
     

  • C

    (c) 57300 years
     

  • D

    (d) 57.3 years

  Explanation

  ? Explanation: C-14 has a half-life of 5730 years, used for archaeological dating.

• 18

  18. Half-life is the time required for —

   

  • A

    (a) All radioactive atoms to decay
     

  • B

    (b) Half of radioactive atoms to decay
     

  • C

    (c) One atom to decay
     

  • D

    (d) Stable atoms to decay

  Explanation

  ? Explanation: Half-life = Time in which half the radioactive sample decays.

• 19

  19. Nuclear fission involves —

   

  • A

    (a) Combining light nuclei
     

  • B

    (b) Splitting a heavy nucleus
     

  • C

    (c) Emission of photons
     

  • D

    (d) Conversion of neutrons to protons

  Explanation

  ? Explanation: Fission = Splitting of heavy nucleus (U-235) → smaller nuclei + neutrons + energy.

• 20

  20. The process in the Sun that releases energy is —

   

  • A

    (a) Nuclear fission
     

  • B

    (b) Nuclear fusion
     

  • C

    (c) Chemical reaction
     

  • D

    (d) Combustion

  Explanation

  ? Explanation: Sun’s energy is due to fusion of hydrogen nuclei into helium.

• 21

  21. In a chain reaction —

   

  • A

    (a) Reaction stops after one step
     

  • B

    (b) Number of reactions multiplies automatically
     

  • C

    (c) Requires continuous external input
     

  • D

    (d) Energy decreases with time

  Explanation

  ? Explanation: Each fission releases neutrons that trigger more fissions → chain reaction.

• 22

  22. The particle emitted during radioactive decay that carries no charge and has high penetration power is —

   

  • A

    (a) Alpha
     

  • B

    (b) Beta
     

  • C

    (c) Gamma
     

  • D

    (d) Neutron

  Explanation

  ? Explanation: Gamma rays are neutral and have maximum penetrating power.

• 23

  23. Which of the following statements are correct?

  1. Protons are positively charged.
  2. Neutrons have no charge.
  3. Electrons have mass equal to that of protons.
  4. Nucleus contains protons and neutrons.
  • A

    (a)  only 1

  • B

    (b)  2 and 3

  • C

    (c) 1, 2 nad 4

  • D

    (d)  All  are Correct

  Explanation

  ? Explanation: Electrons have negligible mass (~1/2000 of proton).

• 24

  24. Which statement is FALSE about Bohr’s atomic model?

   

  • A

    (a) Electrons revolve in fixed orbits.
     

  • B

    (b) Energy of electron orbits is quantized.
     

  • C

    (c) Electrons radiate energy continuously.
     

  • D

    (d) Energy is emitted or absorbed when electrons jump between orbits.

  Explanation

  ? Explanation: Bohr stated that electrons do not radiate energy while in stationary orbits.

• 25

  25. The stability of a nucleus depends on —

   

  • A

    (a) Number of electrons
     

  • B

    (b) Number of neutrons and protons
     

  • C

    (c) Nuclear force
     

  • D

    (d) Both (b) and (c)

  Explanation

  ? Explanation: A nucleus is stable if the neutron–proton ratio is balanced and nuclear force binds them strongly.