SSC CHSL 2022 · Question 34 of 92
Geography
The correct answer is The size of the nucleus is very large as compared to the size of the atom. Key Points RUTHERFORD’S MODEL OF AN ATOM Ernest Rutherford was interested in knowing how the electrons are arranged within an atom. Rutherford designed an experiment for this. In this experiment, fast-moving alpha (α)-particles were made to fall on a thin gold foil. He selected a gold foil because he wanted as thin a layer as possible. This gold foil was about 1000 atoms thick. α-particles are doubly-charged helium ions. Since they have a mass of 4 u, the fast-moving α-particles have a considerable amount of energy. It was expected that α-particles would be deflected by the sub-atomic particles in the gold atoms. Since the α-particles were much heavier than the protons, he did not expect to see large deflections. But, the α-particle scattering experiment gave totally unexpected results. Observations Most of the fast-moving α-particles passed straight through the gold foil. Some of the α-particles were deflected by the foil by small angles. Surprisingly one out of every 12000 particles appeared to rebound. Rutherford concluded from the α-particle scattering experiment that– Most of the space inside the atom is empty because most of the α- particles passed through the gold foil without getting deflected. Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space. A very small fraction of α-particles were deflected by 180 Degrees, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom. From the data, he also calculated that the radius of the nucleus is about 105 times less than the radius of the atom. On the basis of his experiment, Rutherford put forward the nuclear model of an atom, which had the following features: There is a positively charged center in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus. The electrons revolve around the nucleus in circular paths. The size of the nucleus is very small as compared to the size of the atom.Therefore 1st option is not correct regarding Rutherford's nuclear model of an atom . Drawbacks The revolution of the electron in a circular orbit is not expected to be stable. Any particle in a circular orbit would undergo acceleration. During acceleration, charged particles would radiate energy. Thus, the revolving electron would lose energy and finally fall into the nucleus. If this were so, the atom should be highly unstable, and hence matter would not exist in the stable form.
Source: SSC CHSL 2022 (Tier-I) Previous Year Paper (21-Mar-2023) (Shift 2) — prepp.in solved paper · reliable-secondary
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