UC Berkeley, EECS Department
B. E. Boser
EECS 40
HW2: Electronic Circuits
UID:
1. In this problem we investigate charge neutrality.
The force between two electrical charges
q
1
and
q
2
at distance
r
can be calculated using Coulomb’s law,
F
c
=
1
4
πe
0
q
1
q
2
r
2
(1)
a) Calculate the absolute value of the electrostatic force between an electron and a proton at distance
r
=
mm.
1 pt.
0
b) From the assumption that the net charge on every circuit component remains zero at all times, it follows
that currents
i
1
and
i
2
are equal in the circuit shown below.
To get a better feel for the assumption,
let’s assume instead that
i
1
=
0 A and
i
2
=
mA. Then negatively charged electrons accumulate on
X
2
, leaving behind positively charged atomic nuclei on
X
1
. Calculate the attractive force (it is positive)
between
X
1
and
X
2
after
t
=
1 s for
X
1
and
X
2
at a distance of
mm (treat
X
1
and
X
2
as point charges).
1 pt.
1
c) How many loaded trucks weighing
m
=
40000 kg each can you lift with this force?
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 Fall '07
 ChangHasnain
 Electric charge, EECS Department, B. E. BOSER

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