197:
Picture the Problem:
A large number of carbon atoms are collected together in a system.
Strategy:
Each carbon atom has 6 electrons, and each electron carries a charge equal to
−
e
=
−
1.60×10
−
19
C.
We need only multiply the number of electrons by the amount of charge carried by each.
Solution:
Multiply the
number of electrons by
−
e
:
Insight:
This is a huge amount of charge, but you must keep in mind that carbon atoms are electrically
neutral, so that there is an equal amount of positive charge in the nuclei and the net charge of the carbon
atoms is zero.
23
1
19
6
A
6
6 2 mol
6.022 10 mol
1.60 10
C
1 10 C
QNe
n
N
e
1910:
Picture the Problem:
Removing tape from the dispenser transfers electrons from the dispensed tape to the
remainder.
Strategy:
Find the total amount of charge to be transferred by multiplying the number of electrons transferred
by the charge of an electron (
−
1.60×10
−
19
C).
Then divide by 0.14
μ
C per centimeter to find the total length of
tape required.
Solution:
Divide the total amount of
transferred charge by the charge per cm:
13
19
e
6
1.8 10
1.60 10
C
21 cm
//
0.14 10 C/cm
Ne
Q
L
qq
Insight:
The total charge to be transferred is thus 0.14
μ
C/cm × 21 cm = 2.9
μ
C.
This is enough for the tape to
pick up bits of paper via electrical attraction as in Figure 191.
1925:
Strategy:
Use Coulomb’s law (equation 195) to determine the
magnitudes of the forces exerted on each of the charges.
Remember
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 Fall '06
 Alexandrakis
 Physics, Charge, Electric charge, NC

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