Which one of the following could not be explained by Rutherford's nuclear model ?
- A.Stability of the atom
- B.Presence of nucleus in the centre of an atom
- C.Comparison of sizes of atom and nucleus
- D.Nucleus is positively charged
Correct answer
Explanation
The correct answer is A, Stability of the atom. Rutherford's model could not explain why the orbiting electrons do not fall into the nucleus. According to classical physics, a charged particle moving in a circular path is accelerating and must keep radiating energy. An electron circling the nucleus would therefore lose energy, spiral inwards and collapse into the nucleus within a tiny fraction of a second, so atoms should not be stable. Niels Bohr removed this difficulty in 1913 by proposing fixed orbits in which electrons do not radiate energy. Option B is wrong because the gold-foil experiment led Rutherford to place a tiny, dense nucleus at the centre of the atom. Option C is wrong because the model did compare sizes: the nucleus is about 100,000 times smaller than the atom, which is mostly empty space. Option D is wrong because the strong repulsion of a few alpha particles showed that the nucleus is positively charged. Exam tip: Rutherford = nucleus and empty space; Bohr = stable orbits that explain atomic stability.
Practice Questions
View allThe rate of evaporation of liquid does not depend upon
- A.temperature
- B.its surface area exposed to the atmosphere
- C.its mass
- D.humidity
Show answer
Evaporation is a surface process, so its rate depends on conditions at the surface of the liquid, not on how much liquid there is in total.
Read the full explanation →Which one of the following is considered as a compound ?
- A.Silicon
- B.Tin
- C.Sugar solution
- D.Calcium carbonate
Show answer
Calcium carbonate, CaCO3, is a compound because calcium, carbon and oxygen are chemically combined in it in a fixed ratio.
Read the full explanation →'Altitude sickness' is caused at high altitude due to
- A.high partial pressure of oxygen
- B.low partial pressure of oxygen
- C.low level of haemoglobin
- D.high partial pressure of carbon dioxide
Show answer
As one climbs, air pressure falls, so each breath delivers oxygen at a lower partial pressure and less of it passes from the lungs into the blood.
Read the full explanation →Which one of the following is not a characteristic of a compound?
- A.Composition is variable.
- B.All particles of compound are of only one type.
- C.Particles of compound have two or more elements.
- D.Its constituents cannot be separated by simple physical methods.
Show answer
A compound always has a fixed composition by mass, so a variable composition is a property of mixtures, not compounds.
Read the full explanation →A positively charged particle (alpha-particle) is projected towards west in a horizontal plane. It is deflected towards north in the same plane by a magnetic field. Which one among the following is the direction of the magnetic field?
- A.Towards south
- B.Towards east
- C.Vertically downwards
- D.Vertically upwards
Show answer
The magnetic force on a moving charge is F = q(v × B), and only an upward field turns a westward-moving positive charge towards the north.
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