UPSC Prelims 2001 Q107: Science & Technology – Physics
Match List I with List II
and select the correct answer using the codes given below the Lists:
List I (Characteristic)
I. Zero mass
II. Fractional charge
III. Fractional spin
IV. Integral spin
List II (Particle)
A) Positron
B) Neutrino
C) Quark
D) Phonon
- (a) I - B, II - C, III - A, IV - D
- (b) I - C, II - B, III - D, IV - A
- (c) I - B, II - C, III - D, IV - A
- (d) I - C, II - B, III - A, IV - D
Answer: (a) I - B, II - C, III - A, IV - D
Explanation
Matching particle characteristics with particles
| Characteristic (List I) | Particle (List II) |
|---|---|
| I. Zero mass | B. Neutrino — treated as massless then; now known to have a tiny mass |
| II. Fractional charge | C. Quark — charge +2/3 or −1/3 |
| III. Fractional spin | A. Positron — spin 1/2 (a fermion) |
| IV. Integral spin | D. Phonon — quantum of sound vibration, spin 0 (a boson) |
The neutrino was taken as massless, quarks carry fractional charge, the positron (anti-electron) has spin 1/2, and the phonon has whole-number spin. So the code is I-B, II-C, III-A, IV-D.
Answer: (a) I - B, II - C, III - A, IV - D.
Why each option is right or wrong
- (a) CORRECT. Neutrino, quark, positron, phonon.
- (b) Incorrect. Quarks have fractional charge; neutrinos have no charge.
- (c) Incorrect. The phonon has integral spin, and the positron fractional spin.
- (d) Incorrect. The neutrino, not the quark, was the zero-mass particle.
Key point
Fermions (spin 1/2): electrons, positrons, quarks, neutrinos. Bosons (integer spin): photons, phonons, gluons, Higgs.
Remember
Neutrino ~ zero mass; quark fractional charge; positron spin 1/2; phonon integral spin.
Common mistakes
- Giving the phonon fractional spin.
- Giving the quark zero mass instead of the neutrino.
- Forgetting the positron is spin 1/2 like the electron.
Exam tip
Fix the sure pair first: fractional charge = quark.
Sources
- NCERT Class XII — Physics Part II, chapters 'Nuclei' and 'Dual Nature of Radiation and Matter'
- CERN — The Standard Model (home.cern/science/physics/standard-model)