Nuclei Class 12 Important Questions with Answers PDF

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Q.(1)- What is the source of solar Energy?

Answer- In 1938, Hans Bethe an american scientist informed that nuclear fusion is taking place in sun due to which we are getting continuously energy.

There are 90% hydrogen in core of the sun.Temprature is of the order of 2×10⁷ K. Due to this high temprature,all electrons of these elements come out of their orbits. So these elements are in nuclear state. These lighter nucleous fused to form a heavy nucleous and large amount of energy emitted.

So source of solar energy is nuclear fusion.

Q.(2)- How size of nucleus is related with mass number?

Answer- If mass number ie number of nucleons is large then it occupies more spherical space in nucleus to exist in it . So volume of a nucleus is directly proportional to mass number.

\[V\alpha A\]

V=KA

$\frac{4}{3}\pi {{r}^{3}}=KA$

${{r}^{3}}=\frac{3}{4\pi }KA$

$r={{\left( \frac{3}{4\pi }K \right)}^{\frac{1}{3}}}{{A}^{\frac{1}{3}}}$

$r=K'{{A}^{\frac{1}{3}}}$

$r\alpha {{A}^{\frac{1}{3}}}$

Hence radius of a nucleus is directly proportional to cube root of mass number.

Q.(3)- What is atomic pile?

Answer- It is an arrangement in which controlled nuclear fission reaction is performed. U-235 is used as a fuel in it.

It was first performed in 1942 in chicago university.

Q.(3)- Give a plot of yukawa potential?

Answer- Japanese scientist yukawa, demonstrated the relation between nucleon-nucleon potential energy (U) and distance (r) between them with following graph . which is known as yukawa potential plot.

Q.(4)- What do you mean by critical mass (or critical size) ?

Answer- Minimum mass (or minimum size) of a fissionable material to perform nuclear fission is called critical mass (or critical size).

Q.(5)- What are the utilities of moderator, coolant and controlling rods with reference to nuclear reactor?

Bihar Board -2014

Answer- Moderator- Moderator is used to decelerate fast moving neutrons produced in nuclear fission. Because slow moving neutrons are suitable for nuclear fission. Heavy water (${{D}_{2}}O$) or Beryllium oxide (BeO) or graphite is used as a moderator.

Coolant- Coolant is used to absorb heat energy produced in nuclear fission to produce steam. Which is used to rotate turbine to produce electricity. Air or water or $C{{O}_{2}}$ is used as coolant.

Controlling rod- Controlling rods are used to control nuclear fission reaction. Cadmium and Boron are good absorber of neutrons so these are used as controlling rods.

Q.(6)- Write change in position of atom of an element in periodic table due to emission of alpha and beta particles from its nucleus.

Bihar Board -2017

Answer- ${}_{Z}{{X}^{A}}\to {}_{Z-2}{{Y}^{A-4}}+{}_{+2}H{{e}^{4}}$

When an Alpha particle is emitted from the nucleus of an atom then atomic number is decreased by 2. After which a new element is formed. The new element is 2 places lower (shift left) in the periodic table than the original element.

$_{Z}{{X}^{A}}{{\to }_{Z+1}}{{Y}^{A}}{{+}_{-1}}{{\beta }^{0}}+\overline{\nu }$

When a beta particle is emitted from the nucleus of an atom then atomic number is increased by 1. After which a new element is formed. The new element is one place ahead (shift right) in the periodic table than the original elements.

Q.(7)- Write two properties of $\beta $ rays.

Bihar Board -2021

Answer- Two properties of beta rays are followings

(i) $\beta $ particles are fast moving electrons.

(ii) Its penetrating power is 100 times of $\alpha $ particle.

Q.(8)- What is carbon dating?

Answer- It is a method of finding date (age) of residuals of animals or plants

Since we know that ${{C}^{14}}$ is in very low amount in CO2 of atmosphere. Amount of ${{C}^{14}}$ is in same ratio in carbohydrates, which are photosynthesized by plants to absorb CO2 of atmosphere. These carbohydrates are eaten by animals so amount of ${{C}^{14}}$ is in same ratio in their bodies.

Amount of ${{C}^{14}}$ remains constant in the body of plants or animals as long as they alive. If plants or animals die, due to radio active disintegration amount of ${{C}^{14}}$ begins to decrease.

${}_{6}{{C}^{14}}\to {}_{7}{{N}^{14}}+{}_{-1}{{\beta }^{0}}$

Half life time of ${{C}^{14}}$ is 5568 year. Hence to find out the amount of ${{C}^{14}}$ in residuals of plants and animals Date of their death is determined. The process is called carbon-dating.

Q.(9)- Write two properties of alpha rays.

Bihar Board -2022

Answer- Two properties of alpha rays are followings

(i) alpha particle is a helium nucleus.

(ii) Its penetrating power is 1/100 times of beta particles.

Q.(10)- Explain constitution of atomic nucleus .

Bihar Board -2017

Answer- The central core of an atom which contains total positive charge and most of its mass (more than 99.9 %) is called atomic nucleus. It consists of protons and neutrons . The size of a nucleus is 1/10000 times of the size of an atom.

Q.(11)- Write difference between nuclear fission and radioactivity .

Bihar Board -2017

Answer- Radioactivity-

(i) It is a spontaneous process.

(ii) The rate of radioactive decay can not be controlled.

(iii) Energy releases in the form of gamma rays which is not very large.

Nuclear fission -

(i) It does not occur itself . It occurs when neutrons are bombarded on a heavy nucleus.

(ii) The rate of nuclear fission can be controlled.

(iii) Very large amount of energy releases.