Nuclei Class 12 Important Questions with Answers PDF

     Dear students Nuclei Class 12 Important Questions with Answers PDF have been collected at one place to get you all prepared for your 12th Bihar board exam, as well as for UP board exams ,Jharkhand board exam  ,MP board exams ,Rajsthan board exams ,cbse board exams and other board exams. Visit my nawendu classes youtube channel for more help.                                           
Class 12 Important Questions with Answers PDF

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 2×10 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.
\[V\alpha A\]
$\frac{4}{3}\pi {{r}^{3}}=KA$
${{r}^{3}}=\frac{3}{4\pi }KA$
$r={{\left( \frac{3}{4\pi }K \right)}^{\frac{1}{3}}}{{A}^{\frac{1}{3}}}$
$r\alpha {{A}^{\frac{1}{3}}}$
      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.    

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