Modern Physics Questions and Answers – Page 4

The correct answer is Option A — Helium-3 (³He). Helium-3 is an isotope of HELIUM, NOT hydrogen. The three isotopes of hydrogen are:

1. Protium (¹H) - most common, no neutron
2. 2. Deuterium (²H or D) - has 1 neutron, used in heavy water
3. 3. Tritium (³H or T) - has 2 neutrons, radioactive

Why other options are wrong:

Option B (Protium): IS an isotope of hydrogen with mass number 1.

Option C (Deuterium): IS an isotope of hydrogen with mass number 2.

Option D (Tritium): IS an isotope of hydrogen with mass number 3.

The correct answer is Option D — Dr. Homi Jehangir Bhabha. Dr. Homi J. Bhabha (1909–1966) is known as the 'Father of Indian Nuclear Programme.' He founded the Tata Institute of Fundamental Research (TIFR) in 1945 and established the Atomic Energy Establishment Trombay (AEET) in 1954, which was later renamed Bhabha Atomic Research Centre (BARC).

Why other options are wrong:

Option A (S.N. Bose): Satyendra Nath Bose is known for Bose-Einstein statistics, NOT for initiating atomic research.

Option B (A.P.J. Kalam): Kalam is known for missile program and ISRO, not primarily for atomic research initiation.

Option C (C.V. Raman): Raman is known for Raman Effect (1928 Nobel Prize), not atomic research.

The correct answer is Option D — 274 times. The mass of a pion (pi-meson) is approximately 274 times the mass of an electron. Since electron mass = 9.1 × 10⁻³¹ kg, pion mass ≈ 274 × 9.1 × 10⁻³¹ kg ≈ 2.5 × 10⁻²⁸ kg.

Why other options are wrong:

Option A (50 times): Too low. The actual value is 274 times.

Option B (100 times): Incorrect. The actual ratio is 274.

Option C (200 times): Close but incorrect. The exact value is approximately 274.

The correct answer is Option D — Pion (Pi-meson). Pions (pi-mesons) are responsible for mediating the strong nuclear force between nucleons (protons and neutrons) inside the nucleus. This was proposed by Hideki Yukawa in 1935.

Why other options are wrong:

Option A (Gluon): Gluons mediate the strong force at the quark level (inside protons/neutrons), NOT between nucleons directly.

Option B (Electron): Electrons mediate electromagnetic force (photon exchange), NOT strong nuclear force.

Option C (Neutrino): Neutrinos are involved in weak nuclear force (beta decay), NOT strong nuclear force.

The correct answer is Option C — 10⁻¹² cm. The radius of an atomic nucleus is of the order of 10⁻¹² cm (equivalent to 10⁻¹⁵ m or 1 femtometer = 1 fermi). The formula for nuclear radius is R = R₀ × A^(1/3), where R₀ ≈ 1.2 × 10⁻¹⁵ m.

Why other options are wrong:

Option A (10⁻¹⁴ cm): This value does not correspond to any standard nuclear radius. It is between atomic and nuclear size.

Option B (10⁻¹⁰ cm): This is the atomic radius order (Angstrom scale = 10⁻¸ cm), not nuclear.

Option D (10⁻⁸ cm): This is the approximate order of the size of an atom, NOT the nucleus.

The correct answer is Option A — Positron. A positron is the antiparticle of an electron. It has the same mass as an electron but opposite charge (+1.6 × 10⁻¹⁹ C). It was discovered by Carl Anderson in 1932.

Why other options are wrong:

Option B (Neutrino): A neutrino is a neutral, almost massless particle associated with weak interactions. It is NOT the antiparticle of electron.

Option C (Antineutrino): An antineutrino is the antiparticle of neutrino, not of electron.

Option D (Muon): A muon is a heavier version of electron but is NOT its antiparticle.

The correct answer is Option A — Stable. When the neutron-to-proton (n/p) ratio equals 1, the nucleus is stable. This means there is a balanced number of neutrons and protons, which is the most stable configuration for lighter nuclei.

Why other options are wrong:

Option B (Unstable): An unstable nucleus has an n/p ratio that deviates from 1.

Option C (Radioactive): Radioactive nuclei have imbalanced n/p ratios and undergo decay.

Option D (Fissionable): Fissionable refers to nuclei that can split under neutron bombardment (like Uranium-235).

The correct answer is Option D — James Chadwick. James Chadwick, a British physicist, discovered the neutron in 1932. The neutron is a neutral (no charge) subatomic particle found in the nucleus of atoms.

Why other options are wrong:

Option A (Ernest Rutherford): Rutherford proposed nuclear model and discovered proton existence, but NOT neutron.

Option B (Goldstein): Goldstein discovered canal rays (positive rays/protons) in 1886, NOT neutrons.

Option C (J.J. Thomson): Thomson discovered the electron in 1897, NOT neutron.

— 1.67 × 10⁻²⁷ kg. A proton is a positively charged subatomic particle found in the nucleus of every atom. Its mass is approximately 1.67 × 10⁻²⁷ kg (more precisely 1.6726 × 10⁻²⁷ kg). The proton is about 1836 times heavier than the electron.

Why other options are wrong:

Option A (9.1 × 10⁻²⁷ kg): This is not a standard particle mass value. It is incorrect.

Option B (9.1 × 10⁻³¹ kg): This is the mass of an ELECTRON, not a proton.

Option D (1.67 × 10⁻³¹ kg): This value is incorrect. While the coefficient 1.67 is correct for proton, the exponent should be -27, not -31.

The correct answer is Option A — Eugen Goldstein. Eugen Goldstein, a German physicist, discovered canal rays (also called positive rays or anode rays) in 1886. These are positively charged rays that move towards the cathode in a gas discharge tube.

Why other options are wrong:

Option B (J.J. Thomson): J.J. Thomson discovered the ELECTRON (cathode rays) in 1897, NOT canal rays.

Option C (James Chadwick): James Chadwick discovered the NEUTRON in 1932, NOT canal rays.

Option D (Ernest Rutherford): Rutherford conducted gold foil experiment and proposed nuclear model of atom, but did NOT discover canal rays.