Atoms and Nuclei Quiz - ICSE Class 12 Physics

Free practice quiz: Atoms and Nuclei (ICSE Class 12 Physics). 13 multiple-choice questions with answers and explanations. Play online, no sign-up needed.

Sample questions

1. In the Rutherford scattering experiment, the scattering angle of alpha particles is primarily determined by:

   1. The kinetic energy of the alpha particle and the impact parameter.
   2. The velocity of the alpha particle and the atomic number of the target nucleus.
   3. The charge of the alpha particle and the radius of the target nucleus.
   4. The mass of the alpha particle and the distance of closest approach.
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   Answer: A. The kinetic energy of the alpha particle and the impact parameter.

   The scattering angle in Rutherford scattering is governed by the Coulomb repulsion between the alpha particle and the target nucleus. The trajectory depends on the initial kinetic energy of the alpha particle and how close it gets to the nucleus, which is quantified by the impact parameter. A smaller impact parameter leads to a larger scattering angle.

2. A radioactive isotope has a half-life of 10 years. If a sample initially contains 1000 radioactive nuclei, how many nuclei will remain undecayed after 30 years?

   1. 125
   2. 250
   3. 500
   4. 100
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   Answer: A. 125

   After one half-life (10 years), the number of undecayed nuclei will be 1000/2 = 500. After two half-lives (20 years), it will be 500/2 = 250. After three half-lives (30 years), it will be 250/2 = 125. Alternatively, the number of remaining nuclei is N = N₀(1/2)^(t/T), where N₀ = 1000, t = 30 years, and T = 10 years. N = 1000(1/2)^(30/10) = 1000(1/2)³ = 1000/8 = 125.

3. The Bohr model of the atom successfully explains:

   1. The emission spectrum of hydrogen atom.
   2. The spectral lines of all elements.
   3. The wave nature of electrons.
   4. The existence of neutrons in the nucleus.
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   Answer: A. The emission spectrum of hydrogen atom.

   The Bohr model provided a framework to understand the discrete spectral lines observed in the emission spectrum of the hydrogen atom by postulating quantized energy levels for electrons. It failed to explain the spectra of multi-electron atoms and did not incorporate the wave nature of electrons.

4. The mass number of an isotope of Uranium is 238, and its atomic number is 92. How many neutrons does this nucleus contain?

   1. 92
   2. 146
   3. 238
   4. 330
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   Answer: B. 146

   The mass number (A) is the total number of protons and neutrons in an atomic nucleus. The atomic number (Z) is the number of protons. The number of neutrons (N) is given by N = A - Z. In this case, N = 238 - 92 = 146.

5. Which of the following is a characteristic of gamma decay?

   1. The atomic number and mass number remain unchanged.
   2. The atomic number increases by 1.
   3. The mass number decreases by 4.
   4. It involves the emission of an electron.
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   Answer: A. The atomic number and mass number remain unchanged.

   Gamma decay involves the emission of a gamma ray photon from an excited nucleus. Gamma rays are high-energy photons and do not carry any charge or mass. Therefore, gamma decay does not change the atomic number (number of protons) or the mass number (total number of nucleons) of the nucleus. It simply represents a transition of the nucleus from a higher energy state to a lower energy state.

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