Consider a coin of Example 1.20.


Consider a coin of Example 1.20. It is electrically neutral and contains equal amounts of positive and negative charge of magnitude 34.8 kC. Suppose that these equal charges were concentrated in two point charges separated by

(i) 1 cm [ ̴ (1/2) × diagonal of the one paisa coin].

(ii) 100 m ( ̴  length of a long building), and

(iii) 106 m (radius of the earth).

Find the force on each such point charge in each of the three cases. What do you conclude from these results?


Suppose, q be the magnitude of the charge and r1r2 and r3 be the distances in first, second and third case respectively.

According to the question,

q = ± 34.8 RC =± 3.48 × 10C

r1 = 1 cm = 10‒2 m

r2 = 100 m

r3 = 106 m

Suppose, F1Fand F3 are forces in first, second and third case respectively, then by using

|F| = q2/(4πεor2)

We have, F1 = 1.09 × 1023 N

F2 = 1.09 × 1015 N

F3 = 1.09 × 107 N

Conclusion: When separated as point charges these charges exert an enormous force. It is not easy to disturb electrical neutrality.

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