Nuclei: Physics Class 12 Chapter-13

Key Features of NCERT Material for Class 12 Physics Chapter 13– Nuclei

Quick revision notes

In Chapter 12 of Class 12 : you must have learnt about Atoms. In chapter 13:  you will learn about Nuclei.

Define the Nucleus?

An atom consists of the nucleus which is positively charged. The atomic radius is larger than the nucleus’s radius. The mass of an atom is focused on the nucleus. The atom consists of neutrons which have the same mass as protons. The protons and neutrons are bound with each other with a nuclear force. The energies present in nuclear activities is much larger than that of a chemical process.

Isotopes

When the nuclides have the same number of atoms but a different number of neutrons then it is termed as isotopes.

Radioactivity

The nuclei of certain elements give out α,β,γ rays and each representing as helium nuclei, electrons and electromagnetic radiation respectively. Radioactivity is the sign of instability of the nuclei.

Why fusion requires high temperature?

The nuclei which are light must have sufficient initial energy to overpower the Coulombs law between electrical charges having a potential barrier which is only possible in high temperatures.

Nature of Binding Energy

This shows that nuclear reactions which are exothermic in nature are possible in which when a heavy nucleus undergoes fission or two lighter nuclei fuse together to form nuclei with medium mass.

What is the density of nucleic matter?

The mass density of an atoms does not make it capable of depending upon the size of the nucleus.

.In each atom, the positive charge and mass are thickly aggregated at the focal point of the molecule shaping its core. Over 99.9% mass of the particle is gathered in the core. 

2. Atomic Mass Unit (amu) The unit to communicate nuclear masses is called nuclear mass 

unit. Nuclear mass unit is characterized as 1/12 th of the mass of carbon particle (C12). 

3.Structure of Nucleus The arrangement of a core can be depicted by utilizing the accompanying terms and images. 

(i) Atomic Number Z Atomic number of a component is the quantity of protons present inside the core of a particle of the component. 

Nuclear number = Number of protons = Number of electrons 

(ii) Mass Number A Mass number of a component is the absolute number of protons and neutrons inside the nuclear core of the component. 

Mass number = Number of protons + Number of neutrons = Number of electrons + Number of neutrons for example A=Z.+ N 

4. Size of Nucleus If R is the span of the core having mass number An, at that point 

5.Atomic Density of atomic issue is the proportion of mass of core and its volume. 

6. RadioactivityIt is the marvel of unconstrained deterioration of the core of a molecule with emanation of at least one radiations like α-molecule, β-molecule or γ-beams. 

7. Radioactive Decay It is an atomic change measure in which the radioactive beams are produced from the core of the iota. This cycle can’t be quickened and delayed somewhere near any physical or compound cycle. 

8. Radioactivity Decay Law According to this law, the pace of rot of radioactive particles at any moment is relative to the quantity of iotas present right then and there. 

9. Half-life Half-existence of a radioactive component is characterized as the time during which a large portion of the quantity of molecules present at first in the example of the component rot. 

10. Mean Life/Average Life  Average existence of a radioactive component can be gotten by computing the complete life season of the apparent multitude of particles of the radioactive component and isolating it by the all out number of iotas present at first in the example of the component. 

11. Time required to decay from N0 to N

12. Decay Constant The radioactive rot steady might be characterized as the equal of the time during which the quantity of iotas in a radioactive substance lessens to 36.8% of their underlying number. 

13. Radioactive Displacement Law The law of radioactive dislodging is otherwise called Fajan’s and Soddy law. This law portrays which synthetic component and isotope is made during the specific kind of radioactive rot. 

(i) α- Decay In α-decay, the mass number of the item core is four not as much as that of rotting core while the nuclear number abatements by two. 

(ii) β-Decay In β-rot, the mass number of item core stays same however nuclear number increments or diminishes by one. 

In beta-short rot (β–),an electron and an antineutrino are made and produced from the core through the response given beneath: 

In beta-in addition to rot (β+), a positron and a neutrino are made and transmitted from the core by means of the response given underneath: 

(iii) γ-DecayA γ-beam is transmitted when an or β-rot brings about a little girl core in an energized state. Molecule at that point comes back to ground state by a solitary photon progress or progressive changes including more than one photon. 

14. The SI unit of radioactivity is Becquerel (Bq).

1 Becquerel(Bq) = 1 disintegration/second Other units

(i) Curie The activity of a radioactive sample is said to be one curie.

1 curie (Ci) = 3.7 x 1010 decays/second

(ii) Rutherford The activity of a radioactive sample is said to be one rutherford.

1 rutherford (Rd) = 106 decays/second