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# NCERT Solutions for Class 12 Physics Chapter 13 Nuclei - PDF Download `

Board examiners are always stepwise detailed, look for well-managed, accurate, and clear answers. Most of the questions are further extensions of basic NCERT questions; that’s why students look for mostly Chapter 13 which are accurate and solved with simplicity. This chapter consists of multiple numbers and makes the calculation process a little bit difficult. Thus, in this chapter, Chapter 13 with easy methods and less calculation are most important.
Class 12 Physics Chapter 13 Nuclei has many NCERT questions and examples solved in easy language, you can download them in pdf format so that you can access them if you don't have any internet connection.

### Topics of Class 12 Physics Chapter 13 Nuclei

1. Introduction

2. Atomic Masses and Composition of Nucleus

3. Size of the Nucleus

4. Mass energy and Nuclear Binding Energy

• Mass energy

• Nuclear binding energy

5. Nuclear Force

• Alpha decay

• Beta-decay

• Gamma decay

7. Nuclear Energy

• Fission

• Nuclear reactor

• Nuclear fusion – energy generation in stars

• Controlled thermonuclear fusion.

## Introduction

In this chapter we will discuss Nuclei, dimensions of a nucleus are much smaller than those of an atom. Experiments on scattering of a-particles says that the radius of a nucleus was smaller than the radius of an atom. In other words, an atom is almost empty. If an atom is as big as the size of a classroom, the nucleus would be the size of a pinhead. Nevertheless, the nucleus contains most (more than 99.9%) of the mass of an atom.

### Atomic Masses and Composition of Nucleus

The Nucleus of an atom is a tightly packed arrangement of protons and neutrons. These are the two heavy particles in any atom and hence 99.9% of the mass is concentrated in the nucleus.

Composition of Nucleus :The nucleus has two main components protons and neutrons; the atomic mass of the nucleus is given by A=Z+N, where N is the number of neutrons in the nucleus. Different isotopes of an element have different numbers of neutrons in their own nucleus.

### Size of the Nucleus

By performing scattering experiments in which fast electrons, in place of ɑ-particles, are projectiles that bombard targets made up of various elements, the sizes of nuclei of various elements have been accurately measured.

### Mass energy and Nuclear Binding Energy

Main Features of Binding Energy Curve

The average energy per nucleon needed to split a nucleus into its individual nucleons is called the binding energy per nucleon.

The main features of his curve are listed down below.

• The binding energy per nucleon (Ebn) is key constant and is practically autonomous of the atomic number for nuclei middle mass number (30 < A < 170). The maximum value of the curve is about 8.75 MeV for A = 56 and has a value of the 7.6 MeV for A = 238.

• Binding energy per nucleon is lesser for both small nuclei (A <3 0) and heavy nuclei (A > 170).

The following conclusion can be drawn based on the above two observations:

• To produce binding energy of a few MeV per nucleon, the force is attractive and appropriately strong.

• The range of constancy of binding energy is from 30 < A < 170, which has shown the fact that nuclear force is short-ranged.

• Comparatively, a heavy nucleus A = 240 will have a lower binding energy per nucleon to that of A = 120 nucleus; therefore if a nucleus of A = 240 breaks into two A = 120 nuclei in which nucleons get more tightly bound as it implies that energy is released in the process.

### Nuclear Force

The nuclear force is a force that acts between the protons and neutrons of atoms. The nuclear force binds the protons and neutrons in a nucleus together. This force can also exist between protons and protons, neutrons and protons or neutrons and neutrons. This force is what holds the nucleus together.

The particles that came out from nuclei due to nuclear instability is known as radioactivity. There are three types of radioactivity: alpha radiation, beta radiation, and electromagnetic radiation. The SI Unit of Radioactivity Bq or becquerel.

The law of radioactive decay means that for a particular time, the rate of radioactive disintegration is directly proportional to the number of nuclei of the elements present at that time.

#### Alpha-decay

Alpha decay is a kind of radioactive disintegration in which some unstable atomic nuclei disappear excess energy by spontaneously ejecting an alpha particle. The resulting daughter nuclei have a mass number reduced by four and an atomic number is reduced by two from its parent nuclei.

#### Beta-decay

Beta decay is a kind of radioactive decay in which a beta ray is emitted from a nucleus. During beta decay, the proton in the nucleus is transformed into a neutron and vice versa. If a proton is converted to a neutron, we called this β+ decay.

#### Gamma-decay

Gamma decay is a type of radioactivity in which some unstable atomic nuclei dissipate excess energy by a spontaneous electromagnetic process. In the most regular form of gamma decay, known as gamma emission, gamma rays (photons, or packets of electromagnetic energy, of extremely short wavelength) are radiated.

### Nuclear Energy

Nuclear Energy discharged by nuclear reactions either by fusion or fission. In nuclear fusion, atoms combine themselves to form a larger atom. In nuclear fission, the division of atoms takes place to form smaller atoms by releasing energy. Nuclear power plants produce energy using nuclear fission. The Sun produces energy by using the mechanism of nuclear fusion.

#### Fission

When the nucleus of an atom is divided into lighter nuclei through a nuclear reaction the process is termed as nuclear fission. This decay can be natural spontaneous splitting by radioactive decay, or can actually be done in a lab by achieving necessary conditions (bombarding with neutrinos). The resulting fragments tend to have a combined mass which is less than the original.

The process in nuclear physics in which the nucleus of an atom is divided into two daughter nuclei.

When the Uranium-235 atom is bombarded with a neutron, this atom splits into two lighter nuclei Barium and Krypton.

#### Nuclear Reactor

A nuclear reactor is also known as an atomic pile, it is a device used to initiate and control a sustained nuclear chain reaction. Nuclear reactors are used at nuclear power plants for electricity generation and in ships. Heat from nuclear fission is passed to a working fluid that is water or gas, which runs through steam turbines. These either drive a ship's propellers or turn electrical generators.

#### Nuclear Fusion – Energy Generation in Stars

At the center of the star there is a big amount of mass which is surrounding, squeezing down all sides. Hydrogen gas is found at the core of the stars. It gets crushed together so tightly that four hydrogen nuclei combine to form one helium atom. And this process is called nuclear fusion. In the process some of the mass of the hydrogen atoms is converted into energy in the form of light.

#### Controlled Thermonuclear Fusion

The thermonuclear reaction is a type of fusion in which two light atomic nuclei into a single heavier nucleus by a collision of the two interacting particles with high temperatures as a consequence of which a large amount of energy is released. Thermonuclear fusion refers to nuclear fusion reactions that take place at very extreme high temperatures (for example reactions in the sun). The energy produced during this fusion is extremely high but such reactions cannot be controlled. If we are able to achieve the conditions where such a reaction can take place where we can control its rate, then we can achieve what is called controlled thermonuclear fusion.

## Benefits of NCERT Solutions for Class 12th Physics

Chapter 13 of Class 12th Physics Nuclei is not very tough and not very easy; it is a moderate chapter. After knowing concepts and practising the maximum number of questions, you would find them of a moderate level to solve. Some benefits of Chapter 13 are listed down below:

• Chapter 13 solutions reveal all possible methods of solving concerned problems given in the chapter.

• Chapter 13 solutions will help you to improve marks and performance.

• These solutions are created by our expert physics teachers hence they are completely accurate.

• These solutions covered almost all the tips and tricks for quick solving.

• Chapter 13 will help you learn all the important formulas at one hand only.

• These solutions are well explained in detail with logics; hence each solution explains itself the method of solving.

Question 1 : What is radioactivity?

Question 2 : What are the topics in chapter 13 Physics?

Answer : Following are the topics in chapter 13

1. Introduction

2. Atomic Masses and Composition of Nucleus

3. Size of the Nucleus

4. Mass energy and Nuclear Binding Energy

1. Mass energy

2. Nuclear binding energy

5. Nuclear Force

2. Alpha decay

3. Beta-decay

4. Gamma decay

7. Nuclear Energy

1. Fission

2. Nuclear reactor

3. Nuclear fusion – energy generation in stars

4. Controlled thermonuclear fusion.