Question

I dont understand the binding energy part. Where 8.6 x9.1 +8.2x146 came from?

(b) The graph shows the variation with nucleon number A of the binding energy per nucleon. binding energy per nucleon/MeV 0 20 40 60 80 100 120 140 160 180 200 220 240 nucleon number A Plutonium (3Pu) undergoes nuclear fission according to the reaction given below Calculate the number x of neutrons produced. Use the graph to estimate the energy released in this reaction 121 (ii) binding energy of plutonium is 7.6x 239- 1816 1800 MeV (known in (ii)) binding energy of products is 8.6x91+8.2x146 1980 2000 MeV energy released is (2000-1800) 200 MeV

Answer 1

For the binding energy of elements, you are already provided with a graph. So you are confused with the binding energy of products.

First, lets see how to read a graph. On X -Axis , nucleon number is given and on Y-axis, corresponding binding energy per nucleon is given. Note that, the binding energy on Y-axis is per nucleon, it is not for total element. So the binding energy of an element will be the product of nucleon number and the corresponding binding energy.

i.e (binding energy per nucleon)×( nucleon number)

For example,

For Binding energy of Plutonium whose A= 239, you have to see 239 on X- axis , and then find the corresponding binding energy per nucleon on Y -axis.

Now multiply them both.

= 7.6×239

= 1816 Mev

Similarly we are asked for the binding energy of all products.

So you have to add the binding energy of Sr(A=91) and Ba(A=146).

i.e. = 8.6×91+8.2×146 =1980 Mev