Ncert Exercises & Solutions

Fusion processes, like combining two deuterons to form a \({He}\)-nucleus are impossible at ordinary temperatures and pressure. The reasons for this can be traced to the fact:

(a)	nuclear forces have short-range.
(b)	nuclei are positively charged.
(c)	the original nuclei must be completely ionized before fusion can take place.
(d)	the original nuclei must first break up before combining with each other.

Choose the correct option:

1.	(a) and (c)	2.	(a) and (d)
3.	(b) and (d)	4.	(a) and (b)

Hint: The positively charged nuclei repel each other, and the strong nuclear force acts only at very short distances.

Explanation: Fusion processes cannot occur under normal temperatures and pressures because atomic nuclei are positively charged and repel each other, while the strong nuclear force, which can bind them, is both extremely strong and short-ranged. However, at very high temperatures, deuterons gain sufficient average kinetic energy to overcome this electrostatic repulsion and come close enough for the strong nuclear force to take effect, allowing them to fuse.
Therefore, nuclear forces are short-ranged, and nuclei are positively charged.
Hence, option (4) is the correct answer.

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