الفيزياء العامة الجزء الثاني#موقع الفيزياء.كوم

Lectures in General Physics
Example 7.13
A 2.4m length of wire that is 0.031cm 2 in cross section has a measured
resistance of 0.24Ω. Calculate the conductivity of the material.
Solution
L
1
R = ρ and ρ = therefore
A
σ
σ
L .4
=
RA (0.24)(3.1×
10
2 6
=
−
= 3.23×
10 / Ω.
m
6
)
Example 7.14
A 0.9V potential difference is maintained across a 1.5m length of
tungsten wire that has cross-sectional area of 0.6mm 2 . What is the
current in the wire?
Solution
From Ohm’s law,
V
I = where
R
−7
VA 0.9 × 6 × 10
I = =
= 6. 43A
−8
ρL
5.6 × 10 × 1.5
L
R = ρ therefore
A
Dr. Hazem Falah Sakeek