Sources of energy Worksheet-12

Sources of energy Worksheet-12

 

  1. How many groups of nuclei are generated in the fission of  235U ? What are their characteristics ? Explain briefly the terms (i) prompt (ii) delayed, and (iii) spontaneous fission.

 

  1. Write the four processes that can take place, after neutrons are emitted in a fission reaction. Which of these processes will cause the fission to continue? How is the energy of released neutrons lowered from 2 MeV to 0.025 MeV?

 

  1. (i) Draw a schematic diagram to show essential steps in a controlled chain reaction based on   fission of .

(ii) Starting from , describe the chain of nuclear reactions that leads as the final  product. What is the significance of this reaction?

 

  1. a. What type of mirror is used in Box Type Solar Cooker?

b. Why it is difficult to use hydrogen as a source of energy?

c. What is the maximum temperature attained in a concave reflector type solar cooker?

 

  1. Why is solar cooker box covered with a plane glass plate?

 

  1. Why is the energy of water flowing in a river considered to be an indirect form of solar energy?

 

  1. Write one advantage of nuclear fission reaction.

 

Answer:

  1. Two groups of nuclei are generated in the fission of 235U.

One of these is a heavy group of nuclei with mass numbers ranging from 130 to 149, e.g., Barium and Lanthanum.

The other is a lighter group of nuclei with mass numbers ranging from 85 to 104, e.g., Krypton and Molybdenum.

(i) In prompt fission, the heavy nucleus disintegrates the moment it is bombarded.

(ii) In delayed fission, a projectile (e.jg., neutron) enters the target nucleus and causes an instability which results in the fission of the target nucleus after a short while.

(iii) Spontaneous fission is a form of radioactive decay where an atom's nucleus splits into two smaller nuclei and generally one or more neutrons. Spontaneous fission generally in atoms with atomic numbers above 90.

(iv) Spontaneous fission is a relatively slow process except for the heaviest isotopes. For example, uranium–238 decays by alpha decay with a half-life on the order of 109 years, but also decays by spontaneous fission on the order of 1016 years.

 

  1.  

The four process that can place after neutrons are emitted in a fission reaction are :

(i) At least one such neutron hits another nucleus to cause its fission releasing more neutrons.

(ii) The neutrons may be captured by other nuclei without causing their fission.

(iii) The neutrons may be captured by other nuclei (present either in the fissionable material or in the surrounding container without causing fission).

(iv) The neutrons may not interact with other nuclei and may escape the system.

The energy of released neutrons is lowered from 2 MeV to 0.025 MeV by passing them through a moderator.

 

  1. (i) Figure shows the essential steps in a controlled chain reaction based on fission of . FP stands for fission product.90

                                                         

(ii)  (a)             

      (b)      

      (c)

The significance of this chain reaction is that , which is not easily fissionable is converted into (plutonium-239) which can be fissioned easily.

 

  1. a. Plane mirror.

b. It cannot be stored safely as (i) it bums with explosion and (ii) has low ignition temperature.

c. About 200°C.

 

  1. The plane glass plate traps heat radiation and thus produces a kind of greenhouse effect Consequently, the temperature inside the cooker becomes high (100°C to 140°C).

 

  1. Solar energy changes into potential energy of water vapour rising in the atmosphere during evaporation of water from rivers, seas, oceans and other water masses. The water vapour from clouds and also covers mountains with snow. When the clouds bring rain and the snow on the mountains melts, their potential energy changes into kinetic energy of water flowing in the rivers and streams.

 

  1. Amount of energy produced in nuclear fission is enormous, one kg of U-235, on fission produces as much energy as 2500 tons of coal produces on combustion.