Class 12 Physics — Chapter 5: NUCLEI

What you'll learn

• ▸Atomic Mass, Atomic Mass Unit (u), and Isotopes
• ▸Composition of the Nucleus and Nuclear Notation
• ▸Discovery and Properties of the Neutron
• ▸Isotopes, Isobars, and Isotones
• ▸Size and Density of the Nucleus
• ▸Mass-Energy Equivalence

Chapter Summary

--- PAGE 1 --- Chapter Thirteen NUCLEI 13.1 INTRODUCTION In the previous chapter, we have learnt that in every atom, the positive charge and mass are densely concentrated at the centre of the atom forming its nucleus. The overall dimensions of a nucleus are much smaller than those of an atom. Experiments on scattering of α-particles demonstrated that the radius of a nucleus was smaller than the radius of an atom by a factor of about 10⁴. This means the volume of a nucleus is about 10⁻¹² times the volume of the atom. In other words, an atom is almost empty. If an atom is enlarged to the size of a classroom, the nucleus would be of the size of pinhead. Nevertheless, the nucleus contains most (more than 99.9%) of the mass of an atom. Does the nucleus have a structure, just as the atom does? If so, what are the constituents of the nucleus? How are these held together? In this chapter, we shall look for answers to such questions. We shall discuss various properties of nuclei such as their…

Practice Questions from this Chapter

Tap "Get Solution" on any question to ask our AI tutor.

1. Explain why atoms are mostly empty. Get Solution →
2. Give real-world uses for isotopes. Get Solution →
3. Describe nuclear forces simply. Get Solution →
4. What unit is defined as 1/12th the mass of a carbon-12 atom? Get Solution →
5. Who is credited with the discovery of the neutron in 1932? Get Solution →
6. The mass number (A) of a nucleus represents the total number of which particles? Get Solution →
7. What is the general term for a proton or a neutron inside the nucleus? Get Solution →
8. According to Einstein's famous equation, E = mc², mass can be converted into what? Get Solution →

Did you know?

• 💡 An atom is mostly empty space, with its nucleus like a tiny speck.
• 💡 A proton is almost 2000 times heavier than an electron.
• 💡 Some elements have many isotopes, like gold with 32 different versions.
• 💡 A free neutron outside an atom decays in about 15 minutes.
• 💡 The strong nuclear force holds protons and neutrons together tightly.

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