a copper wire of cross sectional area 2.0 mm square carries a current of 10 ampere . a) 1.0×10^1. b)5×10^6 C) 6.3×10^19. d) 3.1×10^25
Answers
Answer:
This is a classic example of a trick question. Sort of.
The last thing you need to worry about is the cross-section of the wire. Here's why.
What is an ampere?
An ampere is the equivalent of one coulomb per second. In your case, a current of
10 A
is equivalent to
10 A
=
10 coulomb
s
How about a coulomb?
A coulomb is the equivalent of roughly
6.241
⋅
10
18
elementary charges, or
1 C
=
6.241
⋅
10
18
×
1.60217662
⋅
10
−
19
C
elementary charge
So if a total charge of
10 C
is passing through the cross-section per second, how many electrons would that be equivalent to?
Well, if
1 C
is equivalent to
6.241
⋅
10
18
electrons per second,
10 C
will be equivalent to
10
C
×
6.241
⋅
10
18
e
−
s
−
1
1
C
=
6.241
⋅
10
18
e
−
s
−
1
Now, the elemental charge is often given as
1.6
⋅
10
−
19
C
, which means that you would get
6.25
⋅
10
18
electrons in one coulomb.
In that case, the answer will indeed be
10
C
×
6.25
⋅
10
18
e
−
s
−
1
1
C
=
6.3
⋅
10
18
e
−
s
−
1
Rounded to two sig figs, of course.
So remember, think about the basic concepts and don't get distracted by "additional information", which can sometimes be misleading.
Explanation:
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