الفيزياء العامة الجزء الثاني#موقع الفيزياء.كوم

Lectures in General Physics
Example 7.4
(a) Calculate the resistance per unit length of a 22 nichrome wire of
radius 0.321mm. (b) If a potential difference of 10V is maintained cross
a1m length of nichrome wire, what is the current in the wire.
ρ nichromes =1.5×10 -6 Ω.m.
Solution
(a) The cross sectional area of the wire is
A = πr 2 = π (0.321×10 -3 ) 2 = 3.24×10 -7 m 2
The resistance per unit length is R/ l
−6
R ρ 1.5×
10
= =
−7
l A 3.24×
10
(b) The current in the wire is
V 10
I = = = 2. 2A
R 4.6
= 4.6Ω
/ m
Nichrome wire is often used for heating elements in electric heater, toaster and irons, since
its resistance is 100 times higher than the copper wire.
Material
1 Silver 1.59×10 -8
2 Copper 1.7×10 -8
3 Gold 2.44×10 -8
4 Aluminum 2.82×10 -8
5 Tungesten 5.6×10 -8
6 Iron 10×10 -8
7 Platinum 11×10 -8
8 Lead 20×10 -8
9 Nichrome 150×10 -8
10 Carbon 3.5×10 -5
11 Germanium 0.46
12 Silicon 640
13 Glass 10 10 -10 14
Resistivity (Ω.m)
Table (7.1) Resistivity of various materials at 20 o C
Dr. Hazem Falah Sakeek