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Nucleus Structure MCQ - Practice Questions with Answers

Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET

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An unstable heavy nucleus at rest breaks into two nuclei which move away with velocities in the ratio of 8:27. The ratio of the radii of the nuclei (assumed to be spherical) is :

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Nucleus Structure

An atom is the basic unit of matter. 

The atom consists of a central core called ‘nucleus’ and the electrons revolve around it in nearly circular orbits as shown in the below figure.

The nucleus of an atom consists of neutrons and protons, collectively referred to as nucleons. The neutron carries no electrical charge and has a mass slightly larger than that of a proton.

Constituents of the nucleus (Nucleons)-

(a) Protons:-

Mass of proton, mp=1.6726×1027 kg
Charge of proton =1.602×1019C
(b) Neutron:-

Mass of neutron, mn=1.6749×1027 kg
The proton is the main part of an atom and carries a positive charge. The number of protons and neutrons is usually the same except in the case of the hydrogen atom which contains a single proton that exists on its own.

The number of protons in a nucleus (called the atomic number or proton number) is represented by the symbol Z.

The number of neutrons (neutron number) is represented by N .
The total number of neutrons and protons in a nucleus is called its mass number and it is represented by N .

And we have A=Z+N.

Note- Mass of electron, proton \& neutron in terms of energy-

me=0.511Mev/c2mp=938.27Mev/c2
 

mn=939.56Mev/c2


Where 1amu=931.5Mev/c2
It is very useful to calculate energy emitted in the nuclear process.
Different types of nuclei-
- Isotopes- The atoms of an element having the same atomic number but a different mass numbers are
called isotopes. All isotopes have the same chemical properties.
The isotopes of some elements are the following 1H1,1H2,1H3 and 8O16,8O17,8O18
- Isobars: The nuclei which have the same mass number (A) but a different atomic number ( Z ) are called isobars. Isobars occupy different positions in the periodic table so all isobars have different chemical properties.

Some of the examples of isobars are 1H3 and 2He3,6C14 and 7 N1488O17 and 9 F17

  • Isotones: The nuclei having an equal number of neutrons are called isotones. For them both the atomic number (Z) and mass number (A) are different, but the value of (N=A–Z) is the same.

Some examples are 44Be9 and 5 B1066C13 and 7N14,gO18 and 9 F19
Size of the nucleus-
- Nuclear radius - The radius r of the nucleaus depends upon the atomic mass A of the element as

R=R0A1/3 where R0= Constant =1.2fm and A= Mass number of the nucleus 

- Nuclear volume: The volume of the nucleaus is given by

V=43πr3=43R03A i.e VA

- Nuclear density: Mass per unit volume of a nucleus is called nuclear density. And it is given as

ρ=MVρ=(A)mp4π3R3ρ=Amp4π3R03A=3mp4πR03
 

  i.e Density is constant for all the nucleaus. It is independent of size and mass numbers.

 

 

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Nucleus Structure

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