P22_028.PDF

28. If the relative diﬀerence between the proton and electron charges (in absolute value) were

q p −|

q e |

=0 . 0000010

then the actual diﬀerence would be

q p −|

q e |

=1 . 6

10 − 25 C .

Ampliﬁed by a factor of 29

10 22 as indicated in the problem, this amounts to a deviation from

perfect neutrality of

∆ q = 29

10 22 1 . 6

10 − 25 C =0 . 14 C

in a copper penny. Two such pennies, at r =1 . 0 m, would therefore experience a very large force.

Eq. 22-1 gives

F = k (∆ q ) 2

r 2

=1 . 7

10 8 N .