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Q.

The resistance of a metal wire of length 1 m is 26 Ω at 20 degree. If the diameter of the wire is 0.3 mm, what will be the resistivity of the metal at that temperature?


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a

1.56 × 10-8 Ω m

b

2.44 × 10-8 Ω m

c

1.26 × 10-8 Ω m

d

1.84 × 10-8 Ω m 

answer is D.

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Detailed Solution

The formula for resistivity is,
Resistivity,
ρ=×Al
Where,
= resistance of the wire
= Area of cross- section
Given that, resistance of wire,
R= 26 Ω,
= 0.3 × 10-3m
Areas of cross-section,
A=πd24 = 3.14 ×(0.3 ×10-3)24     =0.071 × 10-6 m2
On putting all these value in
ρ=×Al      = 26× 0.071 × 10-6 1     = 1.84 × 10-8 Ω m
so at 20 degree the resistivity of wire is 1.84 × 10-8 Ω m.
 
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