Which of the following particles are subatomic particles? 1. Electron 2. Proton 3. Neutron 4. Muon Select the correct answer using the code given below.
- (a)1 and 4 only
- (b)1, 2, 3 and 4
- (c)2 and 3 only
- (d)1, 2 and 3 only
Correct — B, 1, 2, 3 and 4. All four are subatomic particles, because subatomic means smaller than an atom — not necessarily a part of one. Electrons, protons and neutrons are the familiar three, with protons and neutrons in the nucleus and electrons bound around it. The muon is what the question is really about. It is an elementary particle, a lepton like the electron, carrying the same charge of minus one elementary charge and the same spin of one half, but with a mass of 105.66 MeV per c squared — about 206.8 times the electron's. It is not a constituent of ordinary matter only because it is unstable, with a mean lifetime of about 2.2 microseconds, but it is unarguably smaller than an atom and therefore subatomic. Muons were discovered by Carl D. Anderson and Seth Neddermeyer at Caltech in 1936 during cosmic-ray studies, and they rain down on the Earth's surface continuously as decay products of cosmic rays colliding with particles high in the atmosphere.
- (a)1 and 4 only — Keeps the two leptons and drops the proton and the neutron, which are the least controversial subatomic particles on the list — both sit inside the nucleus of every atom heavier than ordinary hydrogen.
- (c)2 and 3 only — A nucleus-only reading. The electron is as subatomic as the proton and the neutron; it simply occupies the space around the nucleus rather than inside it.
- (d)1, 2 and 3 only — The intended trap, and the option most students choose. It silently redefines 'subatomic' as 'found inside an ordinary atom', which excludes the muon. The muon is smaller than an atom, so it qualifies whether or not any atom contains one.
Subatomic particles are simply particles smaller than an atom. Some of them build atoms — protons and neutrons in the nucleus, electrons around it — and some do not, such as the muon, the neutrino and the positron. A further division cuts across that one: protons and neutrons are composite, each made of three quarks, whereas electrons and muons are elementary, with no known internal structure.
The way in is to read the word in the stem literally. 'Subatomic' is a statement about size, and the moment you take it that way the list is settled, because nothing on it is bigger than an atom. Students go wrong by importing a definition the stem never gave — that a subatomic particle must be one of the three that make up an atom — and marking option (d). The muon is a good particle to be tested on, because it is common enough to matter: cosmic rays produce muons in the upper atmosphere at a rate that puts a steady flux through every square metre of the ground, and their survival down to sea level despite a 2.2 microsecond lifetime is one of the standard demonstrations of relativistic time dilation.
- Subatomic means smaller than an atom; it does not require the particle to be a constituent of one.
- The muon is a lepton with charge minus one elementary charge and spin one half, and a mass 206.8 times that of the electron.
- Its mean lifetime is about 2.2 microseconds, which is why muons are not part of ordinary matter.
- Muons were discovered by Carl D. Anderson and Seth Neddermeyer at Caltech in 1936 while they were studying cosmic radiation.
- Muons reaching the Earth's surface are produced indirectly, as decay products of cosmic rays striking particles in the atmosphere.
- Protons and neutrons are composite, each built of three quarks, while electrons and muons are elementary.
Only the first three build atoms; all four are subatomic, which is what the question actually asks.
- Equating 'subatomic' with 'constituent of an atom' and so dropping the muon.
- Assuming an unstable particle is somehow less real than a stable one.
- Treating the electron as outside the atom and therefore not subatomic.
Asked as a select-the-code item where three obvious particles are padded with one unfamiliar name, so the mark turns on the definition of 'subatomic' rather than on any calculation.
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
Same territory — particles beyond the schoolbook three. That UPSC item asks you to place the neutrino, the quark and the positron by charge, mass and spin, which is exactly the wider particle vocabulary that makes the muon unsurprising.
The efforts to detect the existence of Higgs boson particle have become frequent news in the recent past. What is/are the importance/importances of discovering this particle? 1. It will enable us to understand as to why elementary particles have mass. 2. It will enable us in the near future to develop the technology of transferring matter from one point to another without traversing the physical space between them. 3. It will enable us to create better fuels for nuclear fission. Select the correct answer using the codes given below.
- (a) 1 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer(a) 1 only
Same idea of an elementary particle. That UPSC item turns on knowing what 'elementary particle' means and why mass is a question at all — the same framework that places the muon alongside the electron rather than outside the particle zoo.
CDS_GK_2020_II_Q882020Which one of the following statements about the properties of neutrons is not correct?
- (a) Neutron mass is almost equal to proton mass.
- (b) Neutrons possess zero charge.
- (c) Neutrons are located inside the atomic nuclei.
- (d) Neutrons revolve around the atomic nuclei.
Answer(d) Neutrons revolve around the atomic nuclei.
Same building blocks, tested on placement. That 2020 CDS item checks that the neutron sits in the nucleus and does not orbit it; this one checks that being outside the atom altogether still leaves a particle subatomic.
- practice — not a real PYQ
The muon belongs to which one of the following families of particles?
- (a)Quarks
- (b)Leptons
- (c)Bosons
- (d)Hadrons
Answer(b) Leptons — the muon is a heavier cousin of the electron, with the same charge and spin.
- practice — not a real PYQ
Which one of the following is NOT an elementary particle?
- (a)Electron
- (b)Muon
- (c)Proton
- (d)Neutrino
Answer(c) Proton — it is composite, built of three quarks; the other three have no known internal structure.