Question

Find the resistance of the wire of length 20m needed to prepare a coil of resistance 30ohm (Resistivity of material of wire is 2.48×10^-7

Answer 1

Answer:

Explanation:We know that

R=ρ  

4

l

​

 

HEre, R=25Ω, ρ=3.142×10  

−7

Ωm

A=πr  

2

, l=25m

r is the radius of circular cross ectional of wire. So,

⇒ 25=(3.142×10  

−7

)  

(3.142)r  

2

 

(25)

​

 

⇒ r  

2

10  

−7

 

⇒ r=10  

−  

2

7

​

 

=3.16×10  

−3

m

Radius of cross section is 3.16mm