Answer:
8.2 m
Explanation:
We are given that
Potential difference=[tex]V=12 V[/tex]
Diameter=[tex]d=0.25 mm[/tex]
Radius=[tex][r=\frac{d}{2}=\frac{0.25}{2}mm=0.125mm=0.125\times 10^{-3} m[/tex]
[tex]1 mm=10^{-3} m[/tex]
Current= I=4.3 A
Resistivity of copper wire of[tex]\rho=1.68\times 10^{-8}\Omega-m[/tex]
We have to find the length of wire must she use.
We know that
[tex]R=\frac{V}{I}[/tex]
Using the formula
[tex]R=\frac{12}{4.3}[/tex]ohm
[tex]A=\pi r^2=3.14\times (0.125\times 10^{-3})=4.91\times 10^{-8} m^2[/tex]
Using [tex]\pi=3.14[/tex]
[tex]R=\rho\frac{l}{A}[/tex]
[tex]\frac{12}{4.3}=1.68\times 10^{-8}\times \frac{l}{4.91\times 10^{-8}}[/tex]
[tex]l=\frac{12\times 4.91\times 10^{-8}}{1.68\times 10^{-8}\times 4.3}[/tex]
[tex]l=8.2 m[/tex]
Hence, she must use the length of wire =8.2 m
