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Q1. Who is known as the ‘Father’ of nuclear physics?
Ernest Rutherford is known as the ‘Father’ of nuclear physics. He discovered the atomic nucleus through his gold foil experiment in 1911. He also discovered the concept of radioactive half-life and was the first to achieve nuclear transmutation. His work laid the foundation for our understanding of the atom’s structure.
Q2. The instability predicted in Rutherford’s model is because:
The instability predicted in Rutherford’s model is because electrons in circular orbits accelerate. According to classical physics, accelerating charged particles (like electrons) should continuously radiate energy and spiral into the nucleus. This would make atoms unstable. Bohr solved this by proposing that electrons only occupy certain allowed orbits without radiating energy.
Q3. In Rutherford’s gold foil experiment, most α-particles:
In Rutherford’s gold foil experiment, most α-particles passed straight through the foil. This observation led Rutherford to conclude that the atom is mostly empty space. This was a crucial discovery that overturned the earlier atomic models.
Q4. The small fraction of α-particles deflected by 180° indicates:
The small fraction of α-particles deflected by 180° indicates that positive charge occupies very little space. This tiny, dense, positively charged region is the nucleus. The fact that very few particles rebounded showed that the nucleus is extremely small compared to the size of the atom.
Q5. A key feature of Bohr model is that electrons occupy:
A key feature of Bohr’s model is that electrons occupy discrete energy levels (also called orbits or shells). This was a major departure from Rutherford’s model, which allowed any orbit. Bohr proposed that electrons can only exist in certain allowed orbits where they do not radiate energy.
Q6. The positive charge of an atom is concentrated in:
The positive charge of an atom is concentrated in the nucleus. Rutherford’s gold foil experiment demonstrated this. The nucleus contains protons (positively charged) and neutrons (neutral), and it accounts for almost all the mass of the atom. The electrons orbit around the nucleus.
Q7. The gold foil used in Rutherford’s experiment was chosen because it:
The gold foil used in Rutherford’s experiment was chosen because it can be made extremely thin (as thin as 0.0001 mm). Gold is highly malleable and can be hammered into very thin sheets without breaking. This was necessary for the experiment to allow α-particles to pass through the foil.
Q8. Bohr addressed Rutherford’s drawback by suggesting:
Bohr addressed Rutherford’s drawback by suggesting that electrons have discrete energy levels (orbits). According to classical physics, electrons in Rutherford’s model would spiral into the nucleus. Bohr proposed that electrons only occupy certain allowed orbits where they do not radiate energy, solving the instability problem.
Q9. The radius of nucleus is about:
The radius of the nucleus is about 10⁵ times smaller than the atom. The radius of a typical atom is about 10⁻¹⁰ m, while the radius of a nucleus is about 10⁻¹⁵ m. This means the nucleus is about 100,000 times smaller than the atom, yet contains almost all the mass.
Q10. Most of the mass of an atom resides in:
Most of the mass of an atom resides in the nucleus. Protons and neutrons are much heavier than electrons (protons and neutrons are about 2000 times heavier than electrons). The electrons contribute very little to the total mass of the atom.
Q11. The stone and wall analogy explains:
The stone and wall analogy explains the empty space in an atom. Just as a stone thrown at a wall would not pass through, a stone thrown at a wire fence might pass through because of the spaces. Similarly, α-particles mostly pass through atoms because atoms are mostly empty space.
Q12. Bohr wrote which book among his three?
Among his three books, Bohr wrote “Chemistry of Atoms.” His most famous work includes “The Theory of Spectra and Atomic Constitution,” “Atomic Structure and Chemistry,” and “Chemistry of Atoms.” Bohr made significant contributions to atomic physics and chemistry.
Q13. The orbits or shells in Bohr’s model are also called:
The orbits or shells in Bohr’s model are also called energy levels. Each energy level corresponds to a specific amount of energy that the electron can have. Electrons can jump between these energy levels by absorbing or emitting energy.
Q14. In Bohr’s model, electrons in allowed orbits:
In Bohr’s model, electrons in allowed orbits do not radiate energy. This was a key postulate that solved the problem of Rutherford’s model. According to classical physics, accelerating electrons should radiate energy, but Bohr proposed that electrons in certain orbits are stable and do not emit radiation.
Q15. The fraction of α-particles rebounding indicates:
The fraction of α-particles rebounding indicates that the nucleus has nearly all the mass and charge of the atom. When an α-particle hits the nucleus head-on, it rebounds because the nucleus is heavy and positively charged. This showed that mass and positive charge are concentrated in a tiny volume.
Q16. Rutherford compared the rare deflection of α-particles to:
Rutherford compared the rare deflection of α-particles to a 15-inch shell bouncing off tissue paper. This analogy emphasised how surprising it was that a heavy α-particle could be deflected, indicating that there must be a tiny, massive, positively charged nucleus that could repel it.
Q17. Rutherford used α-particles because they are:
Rutherford used α-particles because they are doubly positively charged helium ions (He²⁺). This positive charge made them useful for probing the atom’s structure. They could be deflected by the positive nucleus, providing information about the atom’s internal arrangement.
Q18. Electrons revolve in circular paths around nucleus according to:
Electrons revolve in circular paths around the nucleus according to Bohr. Bohr’s model proposed that electrons move in fixed, circular orbits around the nucleus. Each orbit corresponds to a specific energy level. Rutherford had proposed a similar idea, but Bohr refined it with the concept of quantized orbits.
Q19. Bohr was awarded the Nobel Prize in:
Niels Bohr was awarded the Nobel Prize in Physics in 1922 for his contributions to the understanding of atomic structure and quantum theory. His model of the atom with quantized energy levels was a major breakthrough in atomic physics.
Q20. Bohr wrote the book:
Niels Bohr wrote “The Theory of Spectra and Atomic Constitution.” This book outlined his atomic model and explained the hydrogen spectrum. His work on atomic spectra was fundamental to the development of quantum mechanics.
Q21. In Rutherford’s nuclear model, electrons:
In Rutherford’s nuclear model, electrons revolve around the nucleus in circular paths. The nucleus contains protons and neutrons, while electrons orbit around it. This model was a significant improvement over Thomson’s plum pudding model.
Q22. Rutherford received the Nobel Prize in Chemistry in:
Ernest Rutherford received the Nobel Prize in Chemistry in 1908 for his work on the disintegration of elements and the chemistry of radioactive substances. His earlier research on radioactivity led to this award, even though he is often associated with physics.
Q23. Rutherford’s experiment is also called:
Rutherford’s experiment is also called the gold foil experiment (or α-particle scattering experiment). He bombarded a thin gold foil with α-particles and observed their scattering patterns. This experiment led to the discovery of the atomic nucleus.
Q24. Rutherford concluded the atom is mostly empty space from:
Rutherford concluded that the atom is mostly empty space from the α-particle deflections. The fact that most α-particles passed straight through the gold foil showed that atoms are mostly empty. The rare deflections indicated the presence of a small, dense nucleus.
Q25. The size of the nucleus compared to the atom is:
The size of the nucleus is much smaller than the atom. The nucleus is about 10⁵ times smaller than the atom. It contains almost all the mass but occupies only a tiny fraction of the atom’s volume. Most of the atom is empty space.
Q26. Bohr was appointed professor at Copenhagen University in:
Niels Bohr was appointed professor at the University of Copenhagen in 1916. He later became the director of the Institute for Theoretical Physics in Copenhagen in 1920. His work there attracted many leading physicists.
Q27. The positive charge and mass of an atom are concentrated in:
The positive charge and mass of an atom are concentrated in the nucleus. Rutherford’s gold foil experiment proved this. The nucleus contains positively charged protons and neutral neutrons, and it accounts for virtually all the mass of the atom.
Q28. If electrons radiated energy continuously, atoms would:
If electrons radiated energy continuously, atoms would collapse. According to classical physics, an accelerating charged particle (like an electron orbiting the nucleus) would continuously emit radiation and lose energy. The electron would spiral into the nucleus, causing the atom to collapse. Bohr’s model solved this by postulating stable orbits.
Q29. Most α-particles passed through gold foil because:
Most α-particles passed through gold foil because atoms are mostly empty space. The nucleus is extremely small, and electrons are too light to significantly deflect heavy α-particles. This allowed most particles to pass straight through the foil.
Q30. To overcome Rutherford’s model issues, Bohr proposed:
To overcome Rutherford’s model issues, Bohr proposed discrete allowed orbits for electrons. He suggested that electrons can only exist in certain orbits with specific energies. In these orbits, electrons do not radiate energy, solving the problem of atomic stability.
Q31. Rutherford compared rare α-particle rebounds to:
Rutherford compared the rare α-particle rebounds to a 15-inch shell bouncing off tissue paper. This analogy highlighted the surprising nature of the result—it was as unexpected as a heavy artillery shell being deflected by a piece of paper, indicating a dense, massive nucleus.
Q32. A very small fraction of α-particles were deflected by:
A very small fraction of α-particles were deflected by 180° (reversed direction). This indicated a head-on collision with the nucleus. The fact that they rebounded showed that the nucleus is extremely dense and positively charged.
Q33. Most α-particles passed straight because:
Most α-particles passed straight through because the atom is mostly empty space. The nucleus is very small, and the electrons are too light to deflect the heavy α-particles. Therefore, most particles travelled through the gold foil without any deviation.
Q34. Rutherford was born in:
Ernest Rutherford was born in 1871 in New Zealand. He is considered one of the greatest experimental physicists of all time. He conducted his famous gold foil experiment in 1911 and made many other important discoveries in nuclear physics.
Q35. Bohr received the Nobel Prize for:
Bohr received the Nobel Prize in Physics in 1922 for his work on the structure of atoms. His model of the atom, which introduced the concept of quantized energy levels, was a major contribution to understanding atomic spectra and quantum theory.
Q36. Very few α-particles deviated from their path, indicating:
Very few α-particles deviated from their path, indicating that the nucleus is very small. The fact that only a tiny fraction of α-particles were deflected showed that the positive charge (nucleus) occupies only a minute portion of the atom’s volume.
Q37. The nucleus contains:
The nucleus contains protons and nearly all the mass of the atom. Protons and neutrons are found in the nucleus. The nucleus is positively charged due to protons, and it contains almost all the mass of the atom (99.9% or more).
Q38. Rutherford’s model could not explain:
Rutherford’s model could not explain electron stability. According to classical physics, electrons revolving around the nucleus should radiate energy and spiral into the nucleus. This made the atom unstable, which contradicted the fact that atoms are stable. Bohr addressed this by introducing quantized orbits.
Q39. Bohr’s energy levels are also called:
Bohr’s energy levels are also called atomic shells. These are the different orbits in which electrons can revolve around the nucleus. Each shell corresponds to a specific energy level, and electrons can move between shells by absorbing or emitting energy.
Q40. Electrons revolve around nucleus in Bohr model:
In Bohr’s model, electrons revolve around the nucleus in circular orbits. Each orbit corresponds to a specific energy level. Later, Sommerfeld refined this by introducing elliptical orbits, but Bohr’s original model proposed circular orbits.
Q41. The analogy of child throwing stones demonstrates:
The analogy of a child throwing stones through a wire fence demonstrates the empty space in an atom. Just as stones can pass through the gaps in a fence, α-particles can pass through the empty space in atoms. The rare hits on the wires represent collisions with the nucleus.
Q42. A drawback of Rutherford’s model is that electrons:
A drawback of Rutherford’s model is that electrons would radiate energy while revolving. According to classical electromagnetic theory, accelerating charged particles should emit radiation. This would cause electrons to lose energy and spiral into the nucleus, making atoms unstable.
Q43. The Bohr model postulates electrons occupy:
The Bohr model postulates that electrons occupy only certain discrete orbits (energy levels). Electrons cannot exist between these allowed orbits. When an electron moves from one orbit to another, it absorbs or emits energy equal to the difference between the two levels.
Q44. The radius of the nucleus is about:
The radius of the nucleus is about 10⁵ times smaller than the atom. The atom’s radius is about 10⁻¹⁰ m, while the nucleus’ radius is about 10⁻¹⁵ m. This huge difference means the nucleus is incredibly small compared to the atom.
Q45. Rutherford concluded that most of the atom is:
Rutherford concluded that most of the atom is empty space. This was based on the observation that most α-particles passed straight through the gold foil without being deflected. Only a tiny fraction of α-particles were deflected, indicating the presence of a small, dense nucleus.
Q46. The analogy of stones and a barbed wire fence demonstrates:
The analogy of stones and a barbed wire fence demonstrates α-particle scattering. Just as stones can pass through the gaps in a fence or be deflected by the wires, α-particles pass through the empty space in atoms or are deflected by the nucleus. This analogy helps explain the results of Rutherford’s experiment.
Q47. Bohr’s model solved which problem of Rutherford’s model?
Bohr’s model solved the problem of the stability of electron orbits. Rutherford’s model failed to explain why electrons did not spiral into the nucleus. Bohr proposed that electrons occupy discrete energy levels where they do not radiate energy, thus maintaining stable orbits.
Q48. Bohr was born in:
Niels Bohr was born in 1885 in Copenhagen, Denmark. He became one of the most influential physicists of the 20th century, making fundamental contributions to atomic structure and quantum mechanics. He died in 1962.
Q49. In Bohr’s model, electrons in discrete orbits:
In Bohr’s model, electrons in discrete orbits do not radiate energy. This postulate was essential for explaining atomic stability. Electrons can only emit or absorb energy when they jump between orbits. While in a stable orbit, they do not radiate.
Q50. According to Rutherford, if electrons radiate energy, the atom:
According to Rutherford, if electrons radiate energy while revolving around the nucleus, the atom would collapse. As electrons lose energy, they would spiral inward and fall into the nucleus, making the atom unstable. This was a major flaw in his model that Bohr addressed.