Page 65 - Physics_Form_2

Current electricity

Example 2.8 then,

What is the resistance of a copper wire l = AR
of length 20 m and a diameter of ρ
0.080 cm? (Resistivity of copper, l  4 10  8 m  2 11   0.44 m


ρ =1.68×10 Ωm). 1.0 10  6  m

m.
−8
1.0 10

6
FOR ONLINE READING ONLY
cu
Solution Therefore, the length of the wire is
Given that 0.44 m.
;
l = 20 m for copper,
ρ =1.68×10 Ωm m. 4.9 10  −8  Example 2.10
7
cu A constantan wire has a length of
ρl
R = 45 cm, a diameter of 0.37 mm and
A a resistivity of 4.9 10  7  m.
But A  r 2 (a) What is the resistance of the wire?
 3.14 (4 10   4 m) 2 (b) What will be the current flowing in
the wire if it is connected to a 1.5 V
 5.024 10  7 m 2
cell?
Hence,

m 20 m
1.68 10  8  Solution
R 
5.024 10  7 m 2 (a) ρ =1.0×10 Ωm; m. 1.0 10  6 −6  ; and l = 0.45 m
0.67 
ρl
2
Therefore, the resistance of the wire is But, R = and A  r ;
0.67  . A
where,
Example 2.9 0.37 mm  4


A nichrome wire has a cross-sectional r  2  0.185 mm 1.85 10 m,
2
area of 4 10  8 m and a resistivity r  0.37 mm  0.185 mm 1.85 10  4 m,


of 1.0 10  6  m. If a resistor of 2
resistance 11 Ω is to be made from this hence,
wire, calculate the length of the required A  3.14 (1.85 10   4 m) 2
wire.  1.075 10  7 m 2

Solution 4.9 10  7 
m 0.45 m
Given that, R  1.075 10  7 m 2  2.05 

4 10 m ; ρ =1.0×10 Ωm;; and
A   8 2 1.0 10  −6  m.
6
R  11  ; Resistance of the wire is 2.05 .

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Physics Form 2 Final.indd 59 25/10/2025 10:26