Plus Two Physics Notes Chapter 13 Nuclei is part of Plus Two Physics Notes. Here we have given Plus Two Physics Notes Chapter 13 Nuclei.
|Text Book||NCERT Based|
|Category||Plus Two Kerala|
Kerala Plus Two Physics Notes Chapter 13 Nuclei
Simplified Detailed Notes
Composition of nucleus: An atom consists of a central nucleus containing enitre positive charge and almost entire mass. Nucleus is composed of protons and neutrons.
Atomic number (Z): Number of protons in a nucleus.
Mass number (A): Nubmer of protons + neutrons.
A nuclide is represented by ZXA
Atomic Mass Unit (amu or u): The masses of j atoms, nuclei, etc., are expressed in terms of atomic mass unit. It is defined as 1/12th the mass j of carbon atom (Cth).
1 u = 1.660565 x 10-27 kg
mass of proton (mp) = 1.00727 u
mass of neutron (mn) = 1.00866 u
mass of electron (me) = 0.000549 u
- Isotopes: Same Z and different A.
- Isobars: Same A and different Z.
- Isotones: Same value of A – Z.
Size of Nucleus.
Note: Density of nucleus is constant. It ¡s independent of A.
Mass energy Equivalence Relation
According to Einstein, mass and energy are equivalent. i.e., mass can be converted into energy and vice-versa. It is given by E = mc2
Note: Accordingly 1 kg mass is equivalent to an energy of 931 Me V.
Mass defect: It is the difference of mass of nucleus and total mass of the constituent nucleons.
Am = (ZMp + (A – Z) mn )-M ; where mp and mn are mass of proton and neutron respectively and M is the mass of the nucleus.
Binding Energy and Binding Energy per Nucleon (Eb and Ebn)
The mass defect shown is in the form of binding energy of nucleus, which is responsible for bind¬ing the nucleons into the nucleus. It may be defined as the energy required to split up a nucleus into its constituent nucleons.
Binding energy per nucleon is the ratio of binding energy of nucleus to the number of nucleons.
Note: Ebn is a measure of stability of nucleus. Variation of Binding Energy per Nucleon with Mass number.
- Ebn is almost constant and high for nuclei whose mass number ranges as 30 < A <170.
- The maximum value of Ebn is 8.75Mevfor 56Fe.
- Ebn is low for lighter nuclei and also for heavier nuclie.
Explanation of Nuclear Fission and Fusion:
Nuclear Fission: It is the splitting of heavy nucleus (high mass number) into lighter nuclei of nearly equal masses releasing huge energy. This is because the smaller nuclei have more binding energy per nucleon as nucleons are held more tightly.
Nuclear Fusion: It is the process in which two light nuclei combine to form a single heavier nucleus. The heavier nucleus will have more binding energy per nucleon as nucleons are held more tightly.
- Strongest force in nature.
- It is a short range force.
- It is charge independent.
Plot of potential energy v/s distance.
- Attraction is maximum at r0 = 0.8 fm
- For r < r0, force is repulsive
- For r > r0, force is attractive.
Radioactivity: Many unstable nuclei can decay spontaneously to a nucleus of lower mass but different combinations of nucleons. This process of spontaneous emission of radiation is called radioactivity.
Law of radioactive Decay: According to this law, the rate of decay of radioactive atoms at any instant is proportional to the number of atoms present at that instant in the sample.
Where λ = decay constant and
N = number of undisintegrated nucleus present in the sample at any time t.
N = N0e-λt
N0 = initial amount
Half life(T1/2): It is the time taken for half of the number of atoms in the sample to decay.
Mean Life (Average life): It is defined as the time taken by the sample to reduce to 1/eth t of its initial value.
Radioactive Displacement Laws:
α -decay: In α -decay, mass number is decreased by 4 and atomic number decreased by
β+ -decay: In β+ -decay atomic number is decreased by 1 but mass number remains same.
p → n + e+ + μ
β–-decay: In β–decay atomic number is increased by 1. But mass number remains same
γ -decay: Atom from exited state returns to ground state by emitting γ radiation.
SI unit of radioactivity ¡s Becquerel (Bq)
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